,transcriber's note3 ,text enclosed by underscores is in italics 7italics74 ,text enclosed by equal signs is in bold face 7bold74 ,throughout1 an asterisk 7997 before a name denotes extinct genera_/species4 99 99 99 99 99 ,,university ,,of ,,kansas ,,publications ,,museum ,,of ,,natural ,,history ,vol4 #af1 ,no4 #f1 pp4 #dgc-egi1 #i figures in text ,august #e1 #aifh ,evolution and ,classification of the ,pocket ,gophers of the ,subfamily ,geomyinae ,,by ,,robert ,j4 ,,russell ,,university ,,of ,,kansas ,,lawrence #aifh ,,university ,,of ,,kansas ,,publications1 ,,museum ,,of ,,natural ,,history ,editors3 ,e4 ,raymond ,hall1 ,chairman1 ,henry ,s4 ,fitch1 ,frank ,b4 ,cross1 ,j4 ,knox ,jones1 ,jr4 ,volume #af1 ,no4 #f1 pp4 #dgc-egi1 #i figs4 ,published ,august #e1 #aifh ,,university ,,of ,,kansas ,lawrence1 ,kansas ,,printed ,,by ,,robert ,r4 7,,bob7 ,,sanders1 ,,state ,,printer ,,topeka1 ,,kansas #aifh ,illustration3 ,look for the ,union label #ca-dfbh ,evolution and ,classification of the ,pocket ,gophers of the ,subfamily ,geomyinae ,,by ,,robert ,j4 ,,russell ,,contents ,,page ,,introduction #dgg ,,materials ,,and ,,acknowledgments #dgg ,,taxonomic ,,characters #dgh ,prismatic character of molars #dgh ,character of enamel patterns #dgi ,grooving of incisors #dhj ,masseteric ridge and fossa #dhj ,basitemporal fossa #dha ,specializations of skull #dha ,,fossil ,,record #dhd ,miocene #dhe ,pliocene #dhf ,pleistocene #dij ,thomomys #dib ,zygogeomys #dif ,geomys #dif ,pappogeomys #ejc ,orthogeomys #ejd ,,history ,,of ,,classifications #eje ,,classification #eab ,family ,geomyidae #eab ,subfamily 99,entoptychinae #eac ,genus 99,pleurolicus #ead ,genus 99,gregorymys #ead ,genus 99,grangerimus #ead ,genus 99,entoptychus #ead ,subfamily ,geomyinae #ead ,tribe 99,dikkomyini #eae ,genus 99,dikkomys #eaf ,genus 99,pliosaccomys #eag ,tribe ,thomomyini #eah ,genus ,thomomys #eah ,subgenus 99,pleisothomomys #eai ,subgenus ,thomomys #ebj ,tribe ,geomyini #eba ,genus 99,pliogeomys #ebb ,genus ,zygogeomys #ebc ,genus ,geomys #ebe ,genus ,orthogeomys #ebh ,subgenus ,orthogeomys #ebi ,subgenus ,heterogeomys #ecj ,subgenus ,macrogeomys #eca ,genus ,pappogeomys #ecb ,subgenus ,pappogeomys #ecd ,subgenus ,cratogeomys #ece ,,phylogeny ,,of ,,the ,,geomyidae #ecf ,primitive ,morphotype #ecg ,entoptychid ,radiation #edj ,phyletic ,trends in ,subfamily ,geomyinae #edb ,plio-,pleistocene ,radiation of ,geomyini #eeh ,morphotype #eei ,specializations in ,genera #efj ,zygogeomys #efd ,geomys #efe ,orthogeomys #efh ,pappogeomys #efi ,,literature ,,cited #egb ,,introduction ,when ,c4 ,hart ,merriam wrote his monograph of the subfamily ,geomyinae in #ahie1 he had no opportunity to examine fossil specimens4 ,no doubt his phylogenetic conclusions and classification would have been greatly influenced had he enjoyed that opportunity because study of fossil geomyids reveals the historic sequence of phyletic development1 and this sequence provides a firm basis for distinguishing specialized from primitive characters4 ,the history of the ,geomyinae has been characterized by the evolution of specializations4 ,these evolutionary trends begin1 as we presently know them1 with a generalized ancestral stock in the early ,miocene4 ,the direction1 degree1 and rate of change1 beginning with the primitive morphotype of the subfamily1 has not been the same in the various lineages4 ,the classification within the subfamily is based upon the phyletic interpretations of available data and the relationships they disclose4 ,in turn1 a new1 and ,i hope more realistic1 phylogeny and classification is offered4 ,,materials ,,and ,,acknowledgments ,recent specimens were studied of all the known genera1 subgenera and #bi of the #cf living species4 ,most of the species not studied are monotypic and have restricted geographic ranges4 ,they are3 ,geomys colonus1 ,g4 fontanelus1 and ,g4 cumberlandius1 ,orthogeomys cuniculus and ,o4 pygacanthus of the subgenus ,orthogeomys1 and ,o4 dariensis and ,o4 matagalpae of the subgenus ,macrogeomys4 ,examination of these modern species would not radically change the estimation of the degree of phyletic development of the genera and subgenera involved4 ,all of the major polytypic and widespread species were studied4 ,specimens of the extinct genera ,dikkomys1 ,pliosaccomys1 ,pliogeomys1 ,nerterogeomys1 and ,parageomys also were studied1 as were examples of the extinct species ,geomys quinni1 ,geomys tobinensis1 and ,orthogeomys onerosus4 ,considerable fossil material of living species1 especially of the genera ,geomys and ,pappogeomys1 was used4 ,inasmuch as the present account concerns mainly structural changes in the subfamily ,geomyinae at the level of subgenera and above1 and the temporal sequence of those changes1 no attempt is made in the present account to revise taxonomy below the level of subgenera4 ,considerable modification of the classification below that level 7for species and subspecies7 is to be expected in ,orthogeomys and ,pleistocene taxa of ,geomys when available specimens are studied4 ,i thank ,prof4 ,robert ,w4 ,wilson for his assistance in securing fossil geomyids for study1 and those in charge of the paleontological collections at the ,california ,institute of ,technology1 ,prof4 ,bryan ,patterson1 formerly of the ,field ,museum of ,natural ,history1 and ,prof4 ,claude ,w4 ,hibbard of the ,university of ,michigan1 ,museum of ,zoology4 ,for their kindness in lending ,recent species1 ,i thank ,mr4 ,hobart ,m4 ,van ,duesen of the ,american ,museum of ,natural ,history1 ,dr4 ,david ,h4 ,johnson of the ,u4 ,s4 ,national ,museum1 and ,dr4 ,oliver ,p4 ,pearson of the ,california ,museum of ,vertebrate ,zoology1 the late ,colin ,c4 ,sanborn of the ,field ,museum of ,natural ,history1 and ,profs4 ,emmet ,t4 ,hooper and ,william ,h4 ,burt of the ,university of ,michigan ,museum of ,zoology4 ,i am especially grateful to ,prof4 ,e4 ,raymond ,hall for his guidance and helpful criticisms with the manuscript4 ,for assistance with paleontological problems1 ,i thank ,drs4 ,robert ,w4 ,wilson and ,william ,a4 ,clemens4 ,several persons have offered helpful suggestions and encouragement in the course of my study4 ,for assistance of various sorts ,i especially thank ,drs4 ,j4 ,knox ,jones1 ,jr41 ,rollin ,h4 ,baker1 ,a4 ,byron ,leonard1 ,sydney ,anderson1 ,james ,s4 ,findley1 ,robert ,l4 ,packard1 and ,robert ,g4 ,anderson4 ,advice concerning the drawings of the dentitions was generously given by ,mr4 ,victor ,hogg1 and the drawings were done by ,mrs4 ,lorna ,cordonnier under his direction and by ,mr4 ,thomas ,h4 ,swearingen4 ,for assistance with secretarial tasks ,i thank ,valerie ,stallings1 ,violet ,gourd1 ,ann ,machin1 ,toni ,ward1 ,sheila ,miller1 and my wife1 ,danna ,russell4 ,,taxonomic ,,characters ,morphological features of the fossils and their stratigraphic provenience provide the information upon which phylogenetic interpretations are based4 ,although the most critical sequences of the fossil record are lacking1 and although the existing fossils are mostly fragmentary and therefore seldom furnish ideally suitable data for the interpretations that have been made1 phylogenetic conclusions drawn from fossil materials are superior to those drawn on other bases4 ,the especially relevant characters are those disclosing primary trends in the evolution of the modern assemblages4 ,the higher systematic categories recognized in the following account are based primarily upon such characters4 ,the most important characters found are in the teeth1 although several structural changes in the lower jaw1 especially those associated with the insertion of cranial musculature1 are almost as important4 ,prismatic ,character of ,molars ,in primitive geomyines the molar consisted of two columns united at their mid-points and forming a figure #h or ,h-pattern 7see ,fig4 #d;,b74 ,both labial and lingual re-entrant folds were formed between the two columns4 ,the primitive pattern is retained in the premolars of all known ,geomyinae4 ,therefore1 in the earliest 7,miocene7 members of the subfamily1 the pattern of the molars was essentially like that of the premolars4 ,in ,pliocene ,geomyinae the two columns of the molars tend to merge into one4 ,this is evident on the worn occlusal surface of the teeth2 the lateral re-entrant folds are shallow vertically and progressively recede laterally until only a slight inflection remains4 ,in the final stages of attrition1 the inflection disappears and the tooth is a simple elliptical column4 ,in the ,pleistocene the monoprismatic pattern appears at earlier stages of wear owing to the decrease in depth of the re-entrant folds1 and in ,geomyinae of ,recent time the initial stages of wear on the enamel cap of infants erase the last vestiges of two columns in the molar teeth4 ,the general trend in evolution1 therefore1 has been from a bicolumnar to a monocolumnar pattern4 ,the particular patterns of wear characterizing each genus are described in detail beyond4 ,the third upper molar has evolved less rapidly than the first and second and in one of the modern lineages 7tribe ,geomyini7 tends to retain at least a vestige of the primitive bicolumnar pattern in the final stage of wear4 ,therefore1 the loss of any trace of the bicolumnar pattern in ,m#c is considered to be a much specialized condition4 ,unfortunately1 the fossil record of the third upper molar is less complete than that for the first molar and second molar2 the tooth drops out of its alveolus more often than does any one of the other molariform teeth and is seldom recovered4 ,character of ,enamel ,patterns ,in the primitive genera the enamel pattern is bilophate and the enamel loop 7see ,fig4 #d;,b7 is continuous on the occlusal surface of a worn molar4 ,concomitant with the union of the double columns1 the bilophodont pattern is reduced to a single loph1 but the enamel still completely encircles the dentine4 ,in the molars of modern geomyines1 the enamel loop is not continuous but is interrupted on the sides of the crown by vertical tracts of dentine that are exposed at the occlusal surface of the tooth during early stages of wear4 ,therefore1 a continuous enamel band is to be found only in a juvenal individual whose teeth have been subjected to only slight attrition on the enamel cap4 ,in molars lacking enamel on the labial and lingual sides1 anterior and posterior enamel plates1 or blades1 are found on each molar4 ,the premolar also has an enamel plate on the anterior surface and another on the posterior surface1 and in addition both re-entrant angles are protected by a ,v-shaped investment of enamel4 ,one or the other of the various plates can be reduced or lost accounting for the several distinctive tooth-patterns of the modern geomyines4 ,if loss occurs1 it usually is the anterior plate in the lower dentition and the posterior plate in the upper dentition1 including the upper premolar4 ,when reduction of the posterior plate of the upper cheek teeth occurs1 enamel is first lost from the labial side of the tooth1 thus leaving only a short vestigial plate on the lingual end of the crown4 ,grooving of ,incisors ,the incisors are smooth with no trace of a groove in the ancestral lineage4 ,in the specialized assemblage 7tribe ,geomyini7 pronounced grooves are always developed on the anterior face of the upper incisor4 ,the pattern of grooving is constant in each species and thus provides characters of taxonomic worth for grouping species into genera4 ,the only inconstancy noted was an incisor of ,geomys from the ,tobin local fauna of the middle ,pleistocene which has three grooves rather than the normal two 7,no4 #fgah ,,ku74 ,the extra groove is an obvious abnormality1 and the tooth was associated with others of the same species from the same quarry that were normally grooved4 ,grooves on the lower incisors are unknown4 ,the functional significance of grooving has been debated on numerous occasions in the literature4 ,grooves appear in a number of only distantly related rodents and in lagomorphs4 ,the grooving occurs always in small herbivorous mammals1 and in some way may be related to feeding habits4 ,the grooves provide a serrated cutting edge on the occlusal edge of the upper incisor4 ,in the genus ,geomys1 for example1 the two incisors1 including the slight space between them1 present a total of five serrations1 which may facilitate cutting and piercing tuberous and fibrous roots upon which ,geomys feeds4 ,also the sulci would perform the same function as the longitudinal groove on the side of a bayonet1 and would aid the animal in extracting its upper incisors from coarse1 fibrous material4 ,in gathering food1 the gopher sinks its upper incisors into a root1 and then1 with the upper incisors firmly anchored1 slices off small chunks by means of the lower incisors4 ,therefore1 in pocket gophers1 grooving may be an adaptation for feeding on fibrous or woody material4 ,finally1 grooves increase the enamel surface of the incisor without additional broadening of the tooth itself4 ,there could be a selective advantage for sulcation if the extra enamel and the serrate pattern strengthen the incisors1 which are under heavy stress while penetrating or prying off pieces of coarse material4 ,few broken incisors of pocket gophers are found4 ,masseteric ,ridge and ,fossa ,this ridge and fossa are on the lateral surface of the ramus4 ,the crest on the ridge begins at the base of the angular process and terminates slightly anterior to the plane of the lower premolar4 ,the masseteric fossa receives the insertion of the rostral or superficial division of the masseter muscle4 ,the mental foramen lies immediately anterior1 or anteroventral1 to the fossa4 ,in the ancestral lineage1 the ridge is distinct but relatively low2 the masseteric fossa is shallow and is a poorly developed area for attachment of the superficial masseter muscle4 ,in modern ,geomyinae the ridge is massive and forms a high crest1 especially anteriorly1 and the masseteric fossa is a deep1 prominent cup along the dorsal side of the crest4 ,the elaboration of the crest and fossa evidently is associated with an increase in size of the superficial masseter muscle1 which enlarges and provides increased power for the propalinal type of mastication4 ,a high crest has evolved independently in both modern lineages1 ,thomomyini and ,geomyini4 ,basitemporal ,fossa ,the name basitemporal fossa is suggested here to denote the deep pit that lies between the lingual base of the coronoid process and the third lower molar4 ,the basitemporal fossa receives the insertion of the temporal muscle4 ,the fossa1 which until now has not been named1 is a unique feature in advanced ,geomyinae1 being unknown in either primitive ,geomyinae or in other rodents4 ,the temporal is one of several muscles holding the occlusal surface of the lower molariform dentition firmly against the upper cheek teeth during mastication4 ,in primitive geomyines that masticate food by a planing action1 the temporal muscle also moves the mandible posteriorly and food is ground between the enamel plates when the lower jaw is retracted as well as when it is moved forward4 ,the basitemporal fossa appears in late ,pliocene geomyines and increases the attachment surface of the temporal muscles that powers the planing action important in utilizing woody and fibrous foods4 ,the basitemporal fossa developed in only one of the modern lineages 7tribe ,geomyini71 the same lineage in which grooved incisors evolved4 ,both features probably are adaptations for feeding on coarse food4 ,the fossa is not greatly developed in either the ancestral tribe ,dikkomyini or the modern tribe ,thomomyini1 although in some specimens a slight depression marks the site of the basitemporal fossa4 ,illustration3 ,,fig4 #a4 ,types of skulls in the subfamily ,geomyinae4 #a4 ,a4 and ,b4 ,generalized type of skull4 ,geomys bursarius lutescens1 adult1 male1 ,no4 #ggiee ,,ku1 #aj mi4 ,n ,springview1 ,keya ,paha ,co41 ,nebraska4 ,a4 ,dorsal view of skull4 ,b4 ,ventral view of lower jaw4 ,c4 and ,d4 ,dolichocephalic type of skull4 ,orthogeomys 7,orthogeomys7 grandis guerrerensis1 adult1 female1 ,no4 #cihjg ,,ku1 #a_/b mi4 ,e ,la ,mira1 #cjj ft41 ,michoacn1 ,mxico4 ,c4 ,dorsal view of skull4 ,d4 ,ventral view of lower jaw4 ,e4 and ,f4 ,platycephalic type of skull4 ,pappogeomys 7,cratogeomys7 gymnurus tellus1 adult1 female1 ,no4 #ccded ,,ku1 #c mi4 ,w ,tala1 #dcjj ft41 ,jalisco1 ,mxico4 ,e4 ,dorsal view of skull4 ,f4 ,ventral view of lower jaw4 ,specializations of ,skull ,the skull in most geomyines is generalized1 being neither extremely long and narrow nor short1 broad and flat as in specialized skulls 7see ,fig4 #a74 ,in ,pleistocene lineages of the modern tribe ,geomyini1 long skulls and broad skulls evolved and have been termed dolichocephalic and platycephalic specializations1 respectively by ,merriam 7#ahie3hh-aja74 ,he correlated them with two diametrically different mechanical methods of mastication4 ,in animals with dolichocephalic skulls the principal movements of the mandible in the masticatory process are anteroposterior4 ,the resulting propalinal action of enamel plates in opposition to each other characterizes also animals with a generalized skull1 and evidently is the method of mastication in the primitive geomyines1 but in animals with a dolichocephalic skull the method is developed to a high degree by elongation of the cranium1 mandible1 and teeth4 ,both the mandibular and maxillary tooth-rows are relatively longer than in the generalized skull1 providing a longer block for the planing action of the lower molariform teeth4 ,all teeth1 especially ,p#d and ,m#c1 are longer4 ,in ,m#c the heel 7posterior loph7 in particular is elongated4 ,both the anterior and posterior enamel plates usually are retained in ,m#a and ,m#b4 ,the superficial 7or rostral7 masseter muscle1 originates on the side of the rostrum and inserts in the masseteric fossa and on the masseteric ridge4 ,the deep masseter1 especially the zygomatic part having its origin along the zygomatic arch1 inserts on the angular process of the lower jaw4 ,these two divisions of the masseter muscle have a longer pull 7forward7 in the dolichocephalic skull than in a non-dolichocephalic skull4 ,the temporal and diagastric muscles retract the lower jaws4 ,other1 secondary1 modifications of the dolichocephalic skull are shortening of the angular process of the mandible1 broadening of the rostrum1 and narrowing of the cranium and zygomata4 ,depth of the posterior part of the skull is unchanged4 ,the skull appears to be deep and of nearly equal breadth from nasals to occiput4 ,a good example of a dolichocephalic skull is that of ,orthogeomys 7see ,fig4 #a1 ,c and ,d74 ,in the platycephalic skull1 the principal masticatory movement of the mandible is anterooblique1 to one side and then to the other4 ,the oblique passage of the enamel blades of the lower teeth across those of the upper teeth produces a shearing rather than planing action 7,fig4 #a;,e1 ,f74 ,the anterooblique movement of the lower jaw is possible because of major architectural changes in the cranium and mandible4 ,these changes include3 7#a7 ,broadening of the postrostral part of the skull1 especially the occiput 7mastoidal breadth equals or exceeds zygomatic breadth in skulls of some taxa72 7#b7 flattening of the skull2 7#c7 anteroposterior compression of the molariform teeth1 especially the molars4 ,therefore1 the entire maxillary tooth-row is relatively shorter than in the dolichocephalic skull4 ,only a vestige of the heel ordinarily remains on ,m#c4 ,the loss of the posterior enamel blades of ,p#d1 ,m#a1 and ,m#b eliminates unnecessary friction1 and each of these teeth is wider than long4 ,the distance between the posterior ends of the lower jaws is increased approximately in proportion to the extent that the occiput is widened4 ,as a result of the flattening of the skull the angular processes of the lower jaws are lateral to the zygomatic arches1 and approximately on the same vertical level with them4 ,consequently the insertions of masticatory muscles are shifted laterally4 ,this is especially true of the zygomatic division of the deep masseter1 which inserts on the angular process4 ,contraction of that muscle division of one side of the skull moves the lower jaws obliquely forward4 ,the diagastric and temporal muscles of course retract the lower jaws4 ,the platycephalic skull is the most specialized skull in the ,geomyinae and is a result of the new 7for the ,geomyinae7 method of mastication4 ,the subgenus ,cratogeomys 7see ,fig4 #a1 ,e and ,f7 has a platycephalic skull4 ,the trend toward platycephalic specialization has been the major feature of evolution in ,cratogeomys4 ,,fossil ,,record ,the fossil record of the subfamily ,geomyinae begins in the early ,miocene of western ,north ,america4 ,no geomyids have been recovered from beds of the late ,miocene age4 ,beginning with the early ,pliocene the fossil record becomes progressively more complete1 and geomyines are relatively abundant in deposits of late ,pliocene and ,pleistocene age4 ,although pocket gophers of the subfamily ,geomyinae are rare in lower ,miocene deposits1 members of the subfamily ,entoptychinae are relatively common and highly diversified4 ,four genera and a number of species have been described 7see ,wood1 #aicf3d-be71 and the subfamily ranged widely in western ,north ,america4 ,i interpret this to mean that the geomyines were indeed uncommon in the early ,miocene and their distribution restricted since so few of their remains have been recovered in comparison with entoptychines and the known records are only from the northern part of the ,great ,plains4 ,on the other hand1 entoptychines enjoyed a widespread distribution in western ,north ,america 7see discussion beyond74 ,probably the geographic range of the geomyines was largely allopatric to that of the more specialized entoptychines4 ,the zone of fossoral adaptation for herbivorous rodents is ecologically narrow1 and as a result competition is severe4 ,as a rule1 the outcome of episodes of intergroup competition is geographic exclusion4 ,if these rodents were fossorial in the early ,miocene--their morphology suggests they were at least semi-fossorial--mutually exclusive patterns of distribution are to be expected4 ,miocene ,dikkomys is the only genus of the ,geomyinae known from the early and middle ,miocene4 ,dikkomys matthewi was described by ,wood 7#aicf7 on the basis of isolated teeth from lower ,harrison deposits 7,arikareean in age7 near ,agate1 ,sioux ,county1 ,nebraska4 ,later1 ,galbreath 7#aidh3caf-cag7 described the features of an almost complete mandible recovered from the younger upper ,rosebud deposits1 now considered by ,mac,donald 7#aifc3adi-aej7 to be middle ,miocene1 near ,wounded ,knee1 ,shannon ,county1 ,south ,dakota4 ,more recently ,black 7#aifa3ac7 has described a new species1 ,dikkomys woodi1 from the ,deep ,river ,formation1 ,meagher ,county1 ,montana4 ,the ,deep ,river ,formation is late ,hemingfordian 7middle ,miocene7 in age4 ,no remains of ,dikkomys have been identified in the extensive rodent fauna of the ,john ,day beds of the lower ,miocene of ,oregon1 although entoptychines are abundant in these deposits4 ,in the present account1 ,dikkomys is regarded as the ancestor from which the ,pliocene and modern geomyines were derived4 ,these probably did not evolve from the subfamily ,entoptychinae because the dentition of entoptychines1 especially the premolars and third molars1 was already highly specialized by ,miocene time4 ,the numerous records of ,thomomys and especially ,geomys reported from supposed ,miocene or ,pliocene deposits are without foundation 7see ,matthew1 #ahii3ff2 #aiji3aad1 #aaf1 #aai2 #aiaj3fg1 #gb2 #aibc;a3#cfi2 #aibd3ff2 ,matthew and ,cook1 #aiji3chb2 ,cook and ,cook1 #aicc3di2 and ,simpson1 #aide3hj74 ,most of the records of ,geomys date back to the description of ,geomys bisculcatus ,marsh 7#ahga3aba7 from the ,loup ,fork beds of ,nebraska 7near ,camp ,thomas on the ,middle ,loup ,river74 ,at first ,marsh and other investigators thought these beds were of the late ,miocene age4 ,subsequently the ,loup ,fork fauna was determined by ,matthew 7#aibc;b7 to be mostly early ,pliocene 7,clarendonian71 but with a later ,pleistocene element4 ,recently1 ,schultz and ,stout 7#aidh3efj7 have shown that the various ,loup ,river faunas and also those from along the ,niobrara ,river 7,hay ,springs1 ,rushville1 ,gordon local faunas7 are of middle ,pleistocene age1 the fossil-bearing beds occurring just below the ,pearlette ,ash4 ,these beds are those termed the ,loup ,fork or ,north ,prong of ,middle ,loup by the earlier workers who supposed them to be of ,miocene or ,pliocene age4 ,both ,geomys and ,thomomys have been recovered from most of these deposits1 but they are no older than middle ,pleistocene4 ,this is not surprising in view of the primitive structure of the geomyids known from ,miocene and ,pliocene beds1 but the supposed early appearance of ,geomys and ,thomomys led to much confusion concerning geomyid evolution in the late ,tertiary4 ,the dearth of geomyines in the ,miocene is counterbalanced by the relatively abundant and highly differentiated gophers of the subfamily ,entoptychinae4 ,they reached the zenith of their development in this period4 ,four genera and a number of species are known from the western part of the ,united ,states1 mostly from beds along the ,pacific ,coast and in the northern part of the ,great ,plains4 ,the great diversification of the group in a relatively short period suggests prior movement into a new adaptive zone and subsequent specialization in different subzones and therefore an episode of radial adaptation4 ,the radiation of the entoptychines is discussed elsewhere in the account of geomyid phylogeny1 but it should be noted here that both the ,geomyinae and the ,entoptychinae appear in the fossil record at about the same time in the early ,miocene4 ,the principal distinguishing features of each of the two lineages were well developed at the time of their first occurrence1 and the entoptychines were the more successful in early ,miocene4 ,the ,entoptychinae are known only from the early and middle ,miocene1 unless the earlier deposits of the ,john ,day ,formation of ,oregon from which mammals have been recovered are considered to be latest ,whitneyian 7latest ,oligocene72 for correlations1 see ,wilson 7#aidi3ge74 ,both lineages likely had an earlier history extending back to their divergence in the ,oligocene4 ,pliocene ,the oldest and most primitive ,pliocene geomyine is ,pliosaccomys dubius ,wilson 7#aicf3bj7 from the ,smith ,valley local fauna of middle ,pliocene 7,hemphillian7 age in ,nevada4 ,according to ,wilson 7op4 cit43#ae7 the beds probably were deposited near the middle of ,hemphillian time4 ,shotwell 7#aief3gcj7 recorded ,pliosaccomys dubius from the ,mc,kay ,reservoir and from the ,otis ,basin 7#aifc3gc7 local faunas of the middle ,pliocene 7,hemphillian7 of ,oregon1 and ,green 7#aief3aee7 has recovered remains of ,pliosaccomys 7cf4 dubius7 from the ,wolf ,creek local fauna1 uppermost part of the lower ,pliocene 7late ,clarendonian in age71 of ,shannon ,county1 ,south ,dakota4 ,recently1 ,james 7#aifc3aja7 has described a second species1 ,pliosaccomys wilsoni1 of this primitive genus4 ,the new species was found in early ,pliocene deposits 7late ,clarendonian7 from the ,nettle ,spring local fauna 7,apache ,canyon71 in the ,cuyama ,valley1 ,ventura ,county1 ,california4 ,pliosaccomys wilsoni does not differ greatly from ,p4 dubius2 however1 the few differences in dental characters seem to warrant specific recognition4 ,the reduction of cusps on the metalophid of p#d from three 7dubius7 to two 7wilsoni7 and the lack of accessory cuspules on the protolophid of p#d in wilsoni are probably specializations1 suggesting that ,p4 dubius even though the more recent in age is the less advanced of the two4 ,p4 wilsoni is known only from a lower jaw of a young individual that had dp#d in place1 along with m#a and m#b4 ,the permanent premolar was in the process of erupting1 and the deciduous tooth was removed so that the unworn surface of p#d could be examined4 ,pliosaccomys occurred geographically in the area that the ,entoptychinae had occupied in the early ,miocene4 ,the ,smith ,valley material includes dentitions in almost all stages of wear and the chronological sequences in the development of the patterns of wear can be reconstructed4 ,an understanding of the dental patterns of the primitive geomyines is based mostly on the interpretation of the stages of wear in ,pliosaccomys4 ,no other pocket gopher is known from the area in which ,pliosaccomys occurred1 and it is unknown after middle ,hemphillian age4 ,pliosaccomys has closer affinities with ,dikkomys of the early ,miocene than with any geomyid of the modern assemblage and gives no clue to the origin of the lineage culminating in the modern pocket gophers of the tribe ,geomyini4 ,pliogeomys buisi ,hibbard 7#aied3cec7 was found in the ,buis ,ranch local fauna1 of latest middle ,pliocene1 on the west side of ,buckshot ,arroyo1 ,beaver ,county1 ,oklahoma4 ,the original material included a right ramus bearing the premolar and first two molars 7the holotype7 and five isolated premolars and molars4 ,one of the molars is slightly worn and from an immature individual4 ,one premolar is a deciduous tooth4 ,hibbard 7op4 cit43#cdb7 identified the beds from which he obtained the ,buis ,ranch local fauna as from the lowermost part of the ,upper ,pliocene4 ,moreover1 he judged the ,buis ,ranch local fauna to be only slightly older than the ,saw ,rock ,canyon local fauna of ,seward ,county in southwestern ,kansas4 ,previously 7,hibbard1 #aiec3djh-daj71 the ,saw ,rock ,canyon local fauna had been assessed as older than the ,rexroad local faunas 7latest late ,pliocene7 and1 therefore1 representative of the early part of the late ,pliocene4 ,more recently1 ,hibbard 7#aief3afd7 identified the ,buis ,ranch beds as part of the ,ogallala ,formation1 which here occurs unconformably just beneath the ,rexroad ,formation 7composed of strata nearly all of late ,pliocene age74 ,therefore1 he regarded the ,buis ,ranch beds as latest middle ,pliocene in age4 ,hibbard 7#aied3cef7 suggested that pocket gopher remains from the ,saw ,rock ,canyon local fauna were referable to ,pliogeomys buisi1 and1 in effect1 tentatively assigned them to ,pliogeomys 7in his description of the genus ,hibbard remarked that the upper incisor is bisulcate as in ,geomys1 and the only upper incisor that he mentions was one of the ,saw ,rock ,canyon fossils and not part of the ,buis ,ranch material74 ,pliogeomys has closer affinities with modern pocket gophers of the tribe ,geomyini than it does with the middle ,pliocene genus ,pliosaccomys4 ,the pocket gopher fauna known from the late ,pliocene was more varied than the faunas known from any earlier time4 ,in addition to the extinct ,pliogeomys1 which occurs in early late ,pliocene 7see discussion above71 the living genera ,zygogeomys1 ,geomys1 ,pappogeomys 7in the sense used on p4 #ecd71 and ,thomomys first appear in the late ,pliocene4 ,the only other living genus1 ,orthogeomys1 makes its first appearance in the late ,pleistocene4 ,the earliest record of the genus ,thomomys is based on a fragment of a left mandibular ramus bearing p#d and m#a1 ,thomomys gidleyi ,wilson 7#aicc;b3#abb71 from the ,hagerman local fauna of ,twin ,falls ,county1 ,idaho4 ,wilson 7loc4 cit47 was uncertain as to age 7late ,pliocene or early ,pleistocene7 but subsequently 7#aicg3ch and #fg-gj7 settled on the middle part of the late ,pliocene4 ,hibbard 7#aieh3aa7 later considered the age as early ,pleistocene 7suggesting that the deposits accumulated in the ,aftonian interglacial interval7 but subsequently 7,hibbard et al41 #aife3eab71 on the basis of potassium argon age determinations1 also settled on late ,pliocene4 ,remains of ,nerterogeomys ,zygogeomys have been found in the ,benson local fauna1 ,cochise ,county1 ,arizona1 and the ,rexroad local fauna of ,kansas4 ,this early ,blancan gopher first was described as ,geomys minor by ,gidley 7#aibb3abc71 and was later referred by ,gazin 7#aidb3dhg7 to his new genus ,nerterogeomys4 ,hibbard 7#aiej3ach7 identified specimens from the ,fox ,canyon locality1 one of the localities of ,meade ,county1 ,kansas1 where the ,rexroad local fauna is preserved1 as ,nerterogeomys1 and tentatively referred them to the species ,n4 minor4 ,nerterogeomys cf4 minor has been recovered also from ,locality #c of the ,rexroad local fauna 7,hibbard1 #aiej3aga7 of ,meade ,county1 ,kansas4 ,apparently these are also the small gophers about which ,franzen 7#aidg3eh7 wrote4 ,she assigned them to the genus ,geomys1 and they may actually be a primitive form of ,geomys that represents an intermediate stage in the development of the enamel pattern from the uninterrupted loops of the ancestor to the discontinuous pattern of modern ,geomys4 ,i favor this interpretation2 the evidence1 however1 is inconclusive1 and ,i have1 therefore1 reluctantly allocated them1 along with the other specimens of ,nerterogeomys1 to the genus ,zygogeomys4 ,in an early paper1 ,hibbard 7#aich3bdd7 erroneously referred the same specimens1 two upper premolars of a young individual1 to the genus ,thomomys1 and the same material was identified with the genus ,geomys1 also without specific assignment1 in a later paper 7,hibbard1 #aida;b3#bgh74 ,thomomys is unknown from the late ,pliocene of the ,great ,plains4 ,the specimens previously referred to ,nerterogeomys are assigned to the genus ,zygogeomys for the first time in this report2 for a discussion of the systematic arrangement see the accounts beyond4 ,the type and paratype of ,nerterogeomys from the ,benson local fauna of ,arizona have no indication of enamel reduction4 ,specimens of the genus ,geomys from the late ,pliocene were referred to the large ,geomys quinni ,mc,grew1 first by ,franzen 7#aidg3ee7 and later by ,hibbard and ,riggs 7#aidi3hce7 and ,hibbard 7#aiej3aga74 ,geomys quinni has been obtained from the ,fox ,canyon locality and ,locality #c of the ,rexroad local fauna4 ,at ,locality #c1 both ,zygogeomys 7cf4 minor7 and ,geomys quinni have been found together1 but ,geomys quinni can be distinguished by its much larger size and the advanced enamel pattern of the cheek teeth 7see systematic accounts beyond74 ,all age classes are represented among the specimens of ,geomys quinni2 therefore1 it seems unlikely that the smaller gophers referred to ,zygogeomys are actually the young of ,geomys quinni4 ,hibbard 7personal communication1 ,may1 #aiff7 informed me that specimens of ,geomys from the late ,pliocene 7,fox ,canyon and ,rexroad ,locality #c7 are erroneously referred to ,g4 quinni4 ,according to ,hibbard1 this material represents instead two distinct undescribed species1 descriptions of which have been submitted by him for publication4 ,allocation of late ,pliocene specimens of ,geomys quinni to other species will restrict quinni to the early ,pleistocene4 ,cratogeomys bensoni ,gidley 7#aibb3abc7 was of medium size4 ,the name was based on an upper incisor bearing a single median sulcus and an associated lower jaw containing all of the cheek teeth from the ,benson local fauna1 ,cochise ,county1 ,arizona4 ,additional lower jaws carrying various teeth also were recovered4 ,the specimens might just as well have been assigned to the genus ,pappogeomys since the lower dentitions of all the genera of the tribe ,geomyini have the same enamel pattern1 and the subgenera ,pappogeomys and ,cratogeomys have upper incisors with median grooves4 ,the specimens are too fragmentary to warrant more than generic identification4 ,mainly because of their late ,pliocene age and primitive traits the specimens are here regarded as early representatives of the subgenus ,pappogeomys4 ,discovery of the upper molariform dentition would make a more precise assignment possible4 ,pleistocene ,numerous specimens of geomyids from many localities and horizons are available from the ,pleistocene of ,north ,america4 ,specimens of the genera ,geomys and ,thomomys are especially common4 ,few specimens are known of the genera ,orthogeomys and ,pappogeomys1 especially from the early and middle ,pleistocene1 owing1 probably1 to slight knowledge of the early ,pleistocene of ,mxico where these two genera are thought to have evolved 7see map1 ,figure #b74 ,this lack of knowledge about early ,pleistocene deposits in ,mxico is a handicap in the present instance since the center of differentiation for several of the modern genera is judged to have been in ,mxico1 probably on1 and at the edge of1 the ,central ,plateau4 ,the relative abundance of the remains of ,geomys and ,thomomys from ,pleistocene deposits farther north1 and the marked absence of other genera1 may mean that ,orthogeomys and ,pappogeomys did not range northward from southern and central ,mxico in most of the ,pleistocene4 ,one species of ,pappogeomys eventually ranged into the southwestern ,united ,states in the late ,pleistocene 7toward the end of the ,wisconsin7 and it occurs there today1 but the genus is essentially ,mexican4 ,the fossil record of ,zygogeomys1 as the genus is here understood1 evidently continued in the ,united ,states will into the ,middle ,pleistocene1 depending upon the stratigraphic interpretation of the age of the ,curtis ,ranch local fauna from southeastern ,arizona4 ,hibbard 7#aieh3be7 regarded the ,curtis ,ranch local fauna as ,irvingtonian in age1 a local fauna that lived either in the late ,kansan glacial or the ,yarmouthian interglacial1 and his correlation is tentatively followed here4 ,in deposits laid down later than those of ,irvingtonian age no remains of ,zygogeomys have been found4 ,today a single species exists as a relic in the mountains of central ,mxico and ,zygogeomys may have retreated southward to its present refugium in the late ,pleistocene4 ,perhaps1 ,zygogeomys occurred in northern ,mxico and the southwestern ,united ,states in the early and middle ,pleistocene 7see ,fig4 #b71 occupying the area between the ranges of ,pappogeomys to the south and ,geomys to the north4 ,competition with ,pappogeomys1 and especially ,geomys1 during ,irvingtonian time may have extirpated ,zygogeomys over most of this area1 and by late ,pleistocene 7,sangamon7 much of the former range of ,zygogeomys came to be occupied by one or the other of its competitors4 ,the occurrence of ,geomys garbanii in southern ,california 7see ,white and ,downs1 #aifa7 and the unidentified species of ,geomys in ,aguascalientes 7,mooser1 #aiei2 for faunal correlation1 see ,hibbard and ,mooser1 #aifc71 both from deposits of ,irvingtonian age1 supports this suggestion4 ,illustration3 ,,fig4 #b4 ,probable distribution of the ,subfamily ,geomyinae in the early ,pleistocene 7late ,blancan71 depicting major areas of differentiation of the modern genera4 #a4 ,thomomys #b4 ,geomys #c4 ,zygogeomys #d4 ,pappogeomys #e4 ,orthogeomys ,thomomys ,the earliest ,pleistocene records of ,thomomys are mostly isolated teeth4 ,although they can be identified as genus ,thomomys1 most of the materials are too fragmentary to be identified to species4 ,in ,thomomys two distinct patterns of occlusal surfaces of the molars can be recognized3 the generalized elliptical pattern in the subgenus ,pleisothomomys1 not unlike the pattern in other geomyids1 and the pear-shaped pattern in the subgenus ,thomomys1 which results from constriction of the upper molars on the labial side and constriction of the lower molars on the lingual side4 ,some fossils assigned to ,thomomys were not examined with this distinction in mind by the persons who made the assignments4 ,consequently some of the identifications now in the literature may be subject to change4 ,three occurrences of ,thomomys are from the early and middle ,pleistocene1 with a possible fourth 7depending upon the age of the ,hay ,springs local fauna of ,nebraska74 ,the earliest ,pleistocene record is from the ,broadwater-,lisco beds along the ,north ,platte ,river in ,morrill ,county1 western ,nebraska4 ,possibly the specimen from there was misidentified4 ,those beds are ,lower ,pleistocene1 and are regarded by ,schultz and ,stout 7#aidh3efj-efa1 #egc7 and by ,hibbard 7#aieh3aa71 as having been deposited mostly during the ,aftonian interglacial4 ,there is also some indication that some of the strata were deposited late in the ,nebraskan glaciation4 ,there are no other early ,pleistocene records of ,thomomys4 ,savage 7#aiea3bbh7 reported the genus from the ,irvington local fauna1 ,alameda ,county1 ,california4 ,the specimens were not identified to species1 although they were described as indistinguishable from ,thomomys bottae4 ,paulson 7#aifa3acg7 recorded specimens from the ,cudahy local fauna1 ,meade ,county1 ,kansas4 ,these fragmentary specimens are referable to the subgenus ,thomomys1 owing to the strong constriction of the molars1 but have not been identified to species4 ,the ,cudahy is an ,irvingtonian local fauna1 and is considered to have been deposited during the late ,kansan glaciation4 ,the stratum containing the ,cudahy local fauna immediately underlies the ,pearlette ,ash4 ,the ,cudahy material includes five isolated molars and a fragmentary ramus bearing only the premolar4 ,the genus ,thomomys has been recovered also from the ,hay ,springs local fauna in ,sheridan ,county1 northwestern ,nebraska1 by ,shultz and ,tanner 7#aieg3ga74 ,the ,hay ,springs local fauna is considered to have been deposited in late ,kansan glaciation or in early ,yarmouth interglacial by ,shultz and ,tanner 7op4 cit43#fi71 or of ,irvingtonian age2 however1 ,hibbard 7#aieh3be7 regarded the beds containing this fauna as ,illinoian 7thus post-,irvingtonian in age71 and equivalent in age to the ,berends local fauna of ,oklahoma and the ,butler ,springs and ,mt4 ,scott local faunas of ,kansas4 ,the ,thomomys from ,hay ,springs local fauna has not been referred to species4 ,the relative abundance of ,geomys1 and rarity of ,thomomys1 in ,great ,plains fossil beds of early and middle ,pleistocene is probably due to allopatric distributions of the two genera4 ,the ,great ,plains area was evidently the center of distribution and differentiation of ,geomys4 ,perhaps ,thomomys evolved earlier to the west1 in the ,great ,basin and ,pacific ,coastal regions1 and not on the ,great ,plains4 ,upper ,pleistocene records of ,thomomys are more common4 ,the genus was widespread in beds identified with the ,illinoian and ,sangamon and extended its range eastward to the ,atlantic ,coast4 ,stephens 7#aifj3aifa7 reported ,thomomys from the ,doby ,springs local fauna1 ,harper ,county1 northwestern ,oklahoma4 ,the material 7#cd isolated teeth7 was too fragmentary to permit assignment to species4 ,the molars are constricted on one side1 indicative of the subgenus ,thomomys1 like the ,cudahy specimens reported by ,paulson 7see discussion above74 ,stephens erroneously mentioned that the enamel plate on the posterior face of the upper premolar is unique in ,thomomys2 this plate occurs also in ,zygogeomys4 ,the ,doby ,springs local fauna was recovered from beds that have been identified as ,illinoian deposits1 and it is correlated with the ,berends local fauna in ,beaver ,county1 ,oklahoma1 and the ,butler ,springs local fauna in ,meade ,county1 ,kansas 7see ,stephens1 op4 cit43 #agjj74 ,local faunas in ,maryland and ,florida of ,rancholabrean age include ,thomomys1 in every instance referable to the subgenus ,pleisothomomys on the basis of unconstricted molars4 ,thomomys potomacensis 7,gidley and ,gazin1 #aicc71 from ,cumberland ,cave local fauna1 ,allegany ,county in western ,maryland1 is the type of the genus ,pleisothomomys ,gidley and ,gazin 7#aicc3ced74 ,pleisothomomys is here regarded as a subgenus4 ,the material used in the original description included four lower jaws1 one with a complete dentition4 ,hibbard 7#aieh3be7 pointed out that the ,cumberland ,cave assemblage is a composite fauna including both glacial and interglacial forms4 ,he placed the stratigraphic position of the fauna as definitely ,upper ,pleistocene1 probably deposited in both ,illinoian glaciation and during the ,sangamon interglacial4 ,t4 potomacensis is significantly larger than ,t4 orientalis ,simpson 7#aibh3f71 from the ,saber-tooth ,cave local fauna1 ,citrus ,county1 ,florida4 ,simpson's material included a rostral fragment with an incisor1 premolar1 and first molar4 ,the ,saber-tooth ,cave local fauna is regarded by ,kurten 7#aife3bai7 as having been recovered from ,sangamon deposits4 ,thomomys is unknown from ,wisconsin deposits in the eastern ,united ,states1 and today the genus does not occur east of the ,great ,plains4 ,thomomys of ,rancholabrean provincial age from the western ,united ,states and ,mxico is known only from ,wisconsin beds4 ,three extinct species of ,thomomys1 all referable to the subgenus ,thomomys1 have been described4 ,thomomys microdon ,sinclair 7#aije3adf71 based on the rostral portion of a skull without a mandible1 is from the ,potter ,creek ,cave local fauna1 ,shasta ,county1 ,california1 and has been recovered also from ,samwel ,cave1 ,shasta ,county1 ,california4 ,t4 microdon closely resembles ,thomomys monticola that lives in the area today4 ,thomomys scudderi ,hay 7#aiba3fad7 is from the ,fossil ,lake 7or ,christmas ,lake7 local fauna in central ,oregon4 ,elftman 7#aica3aj-aa7 referred these specimens to ,thomomys townsendii1 and he considered ,t4 scudderi to be a synonym of ,t4 townsendii4 ,davis 7#aicg3aef-aeh7 disagreed with ,elftman concerning the taxonomic status of ,t4 scudderi1 which he regarded as a valid species4 ,according to ,davis1 ,t4 scudderi is more closely allied to ,thomomys bottae than to ,t4 townsendii4 ,cope 7#ahgh3chi2 #ahhi3afj-afe7 had referred the same specimens to ,thomomys clusius 7now ,thomomys talpoides clusius74 ,cope considered the beds to be ,pliocene in age4 ,in all accounts of the ,fossil ,lake local fauna up to ,hay 7#aiba71 the specimens of ,thomomys were referred to the species clusius1 talpoides1 or bulbivorus 7see ,elftman1 loc4 cit474 ,the ,fossil ,lake local fauna is currently considered as being of ,rancholabrean provincial age1 probably dating from the ,wisconsin glacial maximum when the lake reached its greatest size4 ,the third extinct species described from the ,wisconsin is ,thomomys vetus ,davis 7#aicg3aef71 also from the ,fossil ,lake local fauna in ,lake ,county1 ,oregon4 ,davis pointed out that ,t4 vetus differs from ,t4 scudderi ,hay1 of the same fauna1 in larger size and other cranial details1 and that it is closely allied to the living species ,thomomys townsendii1 and not to ,thomomys talpoides1 which is the only species of ,thomomys living in the area today4 ,thomomys townsendii was recovered by ,gazin 7#aice3bii7 from the ,american ,falls beds 7probably ,wisconsin deposits7 in ,idaho4 ,thomomys talpoides is reported from the ,howard ,ranch local fauna in ,hardeman ,county1 western ,texas1 by ,dalquest 7#aife3fi-gj71 who referred the isolated teeth to ,t4 talpoides on geographic grounds1 apparently on the erroneous assumption that ,t4 talpoides was the species of ,thomomys nearest geographically to ,hardeman ,county4 ,hay 7#aibg3bei7 reported ,thomomys fuscus ,thomomys talpoides from late ,pleistocene beds near ,wenatchee1 ,chelan ,county1 ,washington4 ,hibbard 7#aiea3bbi7 recorded ,thomomys talpoides from late ,pleistocene deposits in ,greeley ,county1 ,kansas1 and ,walters 7#aieg3edj7 reported the same species from late ,pleistocene deposits in ,clark ,county1 ,kansas4 ,according to ,hibbard 7#aieh3ad7 other remains reported as ,t4 talpoides have been recovered from numerous areas of ,wisconsin glacial drift in western ,north ,america4 ,thomomys bottae has been identified from ,wisconsin age deposits in western ,north ,america1 as follows3 ,burnet ,cave1 ,gaudalupe ,mt41 ,new ,mexico 7,schultz and ,howard1 #aice3bhj72 ,carpinteria ,asphalt1 ,california 7,wilson1 #aicc;a3#gj72 ,mc,kittrick ,asphalt1 ,kern ,county1 ,california 7,j4 ,r4 ,schultz1 #aich3bjf72 ,rancho ,la ,brea1 ,los ,angeles ,county1 ,california 7,dice1 #aibe3abe--specimens described as a new subspecies1 ,t4 b4 occipitalis72 ,papago ,springs ,cave1 ,santa ,cruz ,county1 ,arizona 7,skinner1 #aidb3aej and #aeh--probably bottae1 but possibly umbrinus on the assumption that the two are specifically instead of subspecifically distinct72 ,isleta ,cave1 ,bernalillo ,county1 ,new ,mexico 7,harris and ,findley1 #aifd3aae--some of these fossils may be post-,wisconsin in age72 ,potter ,creek ,cave and ,samwel ,cave1 ,shasta ,county1 ,california 7,sinclair1 #aije3adf--;identified as ,t4 leucodon1 now a subspecies of ,t4 bottae2 also see ,hay1 #aibg3bad-bae74 ,thomomys umbrinus has been reported from ,san ,josecito ,cave1 ,nuevo ,len1 ,mxico 7,russell1 #aifj3edb72 ,upper ,bercerra1 ,mxico 7,hibbard1 #aiee;a3#ea--;identified only as ,thomomys sp41 but undoubtedly referable to ,t4 umbrinus74 ,post-,wisconsin remains of ,thomomys umbrinus are reported by ,alvarez 7#aifd3f7 from capa ,,ii and capa ,,iii of the ,cueva ,la ,nopalera1 southwestern ,hidalgo4 ,hay 7#aibg3bbb-bbc7 reported specimens of the genus ,thomomys from ,wisconsin deposits in ,hawver ,cave1 ,eldorado ,county1 ,california1 but did not assign them to species4 ,gilmore 7#aidg3aeh7 found the remains of ,thomomys umbrinus in cave deposits near ,quatro ,cinegas in central ,coahuila4 ,these cave deposits may have been laid down during the ,wisconsin1 but more likely accumulated in the post-,wisconsin4 ,zygogeomys ,remains found in the ,curtis ,ranch local fauna1 ,cochise ,county1 in southeastern ,arizona are regarded as of middle ,pleistocene age4 ,see ,gazin 7#aidb3dha-dhd71 ,wilson 7#aicg3ci-dj71 ,hibbard 7#aieh3be71 and ,hibbard et al4 7#aife3eaj-eaa74 ,although some question as to the exact age of the ,curtis ,ranch local fauna still seems to exist1 most authorities on the ,pleistocene agree that the age is not ,pliocene and that it is older than ,rancholabrean4 ,gidley 7#aibb3abb7 described the pocket gopher found in the ,curtis ,ranch beds as ,geomys parvidens1 which is preoccupied by ,geomys parvidens ,brown 7#aijh3aid71 a name proposed for the pocket gopher from the ,conard ,fissure of ,arkansas2 therefore1 ,hay 7#aibg3acf7 proposed the name ,geomys persimilis for the ,curtis ,ranch species to replace ,geomys parvidens ,gidley4 ,geomys persimilis ,hay became the type species of ,gazin's genus ,nerterogeomys 7#aidb3ejg74 ,in this paper1 ,nerterogeomys is considered to be a junior synonym of ,zygogeomys4 ,zygogeomys persimilis is represented by a rostral fragment bearing all the cheek teeth on the left side and the upper incisors4 ,in addition1 two lower jaws1 one with the first three cheek teeth1 are referred to the species 7see ,gazin1 #aidb3ejg74 ,the fossils identified as ,geomys from the ,arroyo ,san ,francisco1 ,cedazo fauna1 in ,aguascalientes1 ,mxico1 by ,mooser 7#aiei3dac7 may be referable instead to ,zygogeomys4 ,i have not seen the specimens and no figures are available2 ,mooser states that a cranium was recovered4 ,if either the upper premolar or third molar is in place1 generic identification could be made with reasonable certainty4 ,no other fossils of ,zygogeomys have been uncovered in late ,pleistocene deposits and the significance of the absence of ,zygogeomys has been discussed in an earlier paragraph of this section4 ,geomys has not been found so far south as ,aguascalientes1 but ,zygogeomys occurs farther south now and presumably had a more extensive range on the plateau to the north in the ,pleistocene4 ,geomys ,geomys is common in ,pleistocene deposits1 especially on the ,great ,plains4 ,certainly the center of differentiation for ,geomys was in this region1 although at times1 probably when conditions were favorable1 ,geomys expanded its range into adjacent areas1 reaching the ,pacific ,coast in ,irvingtonian times and the ,atlantic ,coast at the time of the ,illinoian glaciation4 ,the earliest ,pleistocene records of the genus are from the ,great ,plains4 ,mc,grew 7#aidd3di7 described ,geomys quinni from the ,sand ,draw local fauna1 ,brown ,county1 ,nebraska1 considered by ,hibbard 7#aieh3aa7 to be ,nebraskan in age4 ,as mentioned in the account of ,pliocene geomyids1 ,geomys quinni occurs also in the late ,pliocene deposits of southwestern ,kansas4 ,also1 ,geomys quinni occurs in the ,broadwater-,lisco local fauna of ,morrill and ,garden counties1 western ,nebraska 7,barbour and ,schultz1 #aicg3c2 ,schultz and ,stout1 #aidh3efj-efc2 ,schultz et al41 #aiea3 table #a74 ,the ,broadwater-,lisco is currently regarded as ,aftonian deposits 7,schultz and ,stout1 loc4 cit42 ,hibbard1 #aieh3aa74 ,hibbard 7#aief3agd7 identified ,geomys quinni from the ,deer ,park local fauna1 probably deposited during the early ,aftonian interglacial1 of ,meade ,county1 ,kansas4 ,strain 7#aiff3cf7 described ,geomys paenebursarius on the basis of fossils obtained from early ,pleistocene deposits of the ,hudspeth local fauna from western ,hudspeth ,county in the ,trans-,pecos of ,texas4 ,the ,hudspeth fossils were probably deposited during the ,aftonian interglacial4 ,from ,kingman ,county1 ,kansas1 ,hibbard 7op4 cit43 #afd7 recovered isolated teeth of ,geomys from the ,dixon local fauna1 regarded by him 7op4 cit43#aec-aed7 as deposited during the latest ,nebraskan glaciation1 and correlated by him with the ,sand ,draw local fauna of ,nebraska4 ,hibbard 7#aieh3aa7 later regarded the ,dixon as a transitional fauna between ,nebraskan and ,aftonian4 ,the remains of ,geomys from the ,dixon are known only from isolated teeth4 ,the teeth are small1 and suggest that a smaller species of ,geomys may have occurred along with the more common and larger ,g4 quinni during the early ,pleistocene 7see discussion beyond of the ,saunders ,geomys74 ,geomys quinni was widespread and common throughout the central ,great ,plains from the late ,pliocene 7,rexroad fauna7 through the early ,pleistocene 7,nebraskan and ,aftonian deposits74 ,hibbard 7#aief3agi7 referred the pocket gopher remains taken from the ,saunders local fauna in ,meade ,county1 ,kansas1 to ,geomys tobinensis1 a small species having continuous enamel bands around the lower premolar in younger specimens4 ,the ,saunders local fauna was deposited in the late ,aftonian and is younger than the ,deer ,park local fauna discussed above4 ,paulson 7#aifa3ach7 later pointed out that the ,saunders ,geomys is distinct from ,geomys tobinensis2 hence1 the small pocket gopher from the ,saunders local fauna is probably an unnamed species1 perhaps more closely allied to paenebursarius than to quinni4 ,the small ,geomys reported from the ,aftonian ,broadwater-,lisco local fauna of ,nebraska 7,schultz and ,stout1 #aidh3efc7 may also be the same as the ,saunders pocket gopher1 but the smaller adult specimens occurring in the same bed with larger specimens probably are females and the larger specimens males4 ,in all living ,geomyini females have smaller skulls than males4 ,the ,irvingtonian provincial age is currently regarded as ,middle ,pleistocene and includes the late ,kansan glaciation 7that part occurring after the glacial maximum7 and the ,yarmouthian interglacial 7see ,hibbard et al41 #aife3eab-ead74 ,the ,irvingtonian provincial age1 therefore1 follows the late ,blancan provincial age of the early ,pleistocene and is succeeded by the ,rancholabrean provincial age of the late ,pleistocene4 ,no specimen of an ,irvingtonian ,geomys is referable to any living species4 ,two ,irvingtonian species have been described4 ,hibbard 7#aidd3gce7 named ,parageomys tobinensis ,geomys tobinensis from the ,tobin local fauna of ,russell ,county1 ,kansas4 ,this species since has been reported from the ,cudahy local fauna of ,meade ,county1 ,kansas 7,paulson1 #aifa3acg74 ,hibbard 7#aief3ahc7 also identified as ,geomys tobinensis the pocket gopher recovered from the ,saunders local fauna1 a late ,aftonian deposit of ,meade ,county1 ,kansas1 and reduced the technical name ,parageomys from generic to subgeneric rank4 ,paulson 7op4 cit43#ach7 pointed out that the ,saunders specimens differ from ,g4 tobinensis1 and he1 therefore1 restricted the name to the small ,geomys of the ,cudahy and ,tobin local faunas of ,irvingtonian provincial age4 ,g4 tobinensis is markedly smaller than the ,blancan ,g4 quinni4 ,the ,cudahy and ,tobin local faunas are of approximately the same age1 and presently both are included in one unit1 the ,cudahy fauna4 ,the ,cudahy fauna is considered to have been deposited in late ,kansan as it occurs in strata immediately below the ,pearlette ash4 ,recently1 ,white and ,downs 7#aifa3h7 described a new ,irvingtonian species1 ,geomys garbanii1 from the middle ,pleistocene ,vallecito ,creek local fauna of ,san ,diego ,county1 ,california4 ,many well preserved fossils of the new species were recovered4 ,geomys garbanii is of medium size 7approximately the size of one of the larger subspecies of ,g4 bursarius71 and significantly larger than the ,irvingtonian ,geomys tobinensis of the ,great ,plains4 ,the ,vallecito ,creek occurrence of ,geomys is the first authenticated record from the ,pacific ,coast region4 ,matthew 7#aijb3cbj7 erroneously referred remains of ,thomomys to the genus ,geomys in his revised list of ,cope's earlier report on the ,fossil ,lake 7or ,silver ,lake7 fauna 7see discussion of ,thomomys above74 ,a number of ,irvingtonian fossil remains of ,geomys have not been identified with particular species4 ,hibbard 7#aida;a3#bjf7 found ,geomys in the ,borchers local fauna 7deposited in the time of the ,yarmouthian interglacial7 of ,meade ,county1 ,kansas4 ,also1 ,geomys has been reported from several sites in ,nebraska4 ,schultz and ,tanner 7#aieg3fg7 reported ,geomys from the ,angus fossil quarry in ,nuckolls ,county1 south-central ,nebraska4 ,the ,angus fossils were found in sediments of the ,sappa ,formation considered by ,schultz and ,tanner to be a ,yarmouthian deposit4 ,fossil quarries 7,hay ,springs1 ,rushville1 and ,gordon7 along the south side of the ,niobrara ,river ,valley in ,sheridan ,county1 ,nebraska1 have also provided records of geomyids4 ,both a large and small species of ,geomys have been reported from the more recently excavated ,rushville and ,gordon sites 7,schultz and ,stout1 #aidh3efb-efg1 and table #c74 ,in view of the great disparity in size owing to sex1 these may actually be males and females of the same species1 as mentioned above4 ,the name ,hay ,springs has been used in reference to all three sites4 ,the ages of the ,hay ,springs sites are approximately the same1 but their correlation is presently under debate4 ,schultz and ,tanner 7#aieg3fh-ga7 maintain that the fossils are distinctly middle ,pleistocene1 and that they were deposited during late ,kansan glaciation1 or perhaps from early ,yarmouthian into early ,illinoian1 with the largest concentration coming from the ,sappa sands of pre-,illinoian 7,yarmouth7 age4 ,hibbard 7#aieh3be71 basing his opinion on the presence of ,microtus pennsylvanicus1 and the stage of evolution of other species in the assemblage1 regards the ,hay ,springs sites as probably ,illinoian deposits1 but certainly no older than that4 ,mooser 7#aiei3dac7 identified as ,geomys the pocket gopher from ,irvingtonian deposits in ,arroyo ,san ,francisco 7loc4 no4 #e7 near the city of ,aguascalientes1 ,mxico4 ,as suggested elsewhere in this account1 these fossils may be referable to ,zygogeomys rather than ,geomys4 ,the ,irvingtonian provincial age of this fauna was established by ,hibbard and ,mooser 7#aifc3bde-bej74 ,other alleged occurrences have recently been compiled by ,alvarez 7#aife3ai-bj74 ,maldonado-,koerdell 7#aidh3bj7 noted four fossil occurrences of the genus ,geomys in ,mxico4 ,two of these from ,san ,josecito ,cave in ,nuevo ,len have since been identified with the genera ,orthogeomys and ,pappogeomys 7,russell1 #aifj3edc-edh72 the third listed by ,maldonado-,koerdell from near ,ameca1 ,jalisco1 was based on ,brown's 7#aiab3afg7 mention of some bones supposedly of the family ,geomyidae1 and the fourth refers to pocket gopher remains from the ,hochtals von ,mexiko listed as ,geomys by ,freudenberg 7#aiba3aci74 ,his generic identification is doubtful and the specimens should be compared with ,mexican genera of the ,geomyinae4 ,upper ,pleistocene records of ,geomys also are common4 ,upper ,pleistocene is here understood to include late ,illinoian1 ,sangamon and ,wisconsin deposits2 all are considered to be of ,rancholabrean provincial age 7see ,hibbard et al41 #aife3eab-eae7 and post-,irvingtonian4 ,the presence of remains of ,bison and_/or ,microtus pennsylvanicus are currently considered mammalian index fossils of ,rancholabrean faunas4 ,in the ,illinoian1 ,geomys extended its range to the ,atlantic ,coast in the southeastern ,united ,states4 ,the eastern and western species-groups evidently were isolated throughout much of the late ,pleistocene1 and1 therefore1 evolved separately4 ,of the two1 the eastern1 or pinetis1 species-group seems to have remained somewhat more generalized1 and the western1 or bursarius1 species-group has become more specialized4 ,the ,rancholabrean ,geomys from deposits in the southeastern ,united ,states are referable 7see ,ray1 #aifc3cbe7 to ,geomys pinetis4 ,marsh 7#ahga3aba7 described ,geomys bisulcatus from the ,north ,prong of the ,loup ,river 7near ,camp ,thomas71 ,nebraska4 ,these beds are also termed the ,loup ,fork or ,loup ,river fossil beds 7see discussion on p4 #dhe71 and they lie along the upper reaches of the ,middle ,loup ,river in ,thomas ,county 7near ,senea71 ,hooker ,county 7near ,mullen71 and southeastern ,cherry ,county 7probably the ,north ,prong beds northwest of ,mullen74 ,these beds were at first thought to be of ,miocene age1 but later were regarded as early ,pliocene 7see ,schultz and ,stout1 #aidh3efb-eff for a historical account of expeditions to these fossil sites74 ,schultz and ,tanner 7#aieg3ga-gb7 pointed out that the principal fossiliferous beds in the ,middle ,loup region are of middle to late ,pleistocene age1 with most of the fossils coming from the ,crete sand and silt beds which are probably early ,illinoian deposits1 and1 therefore1 younger than the ,hay ,springs faunas4 ,some fossils may have come from the ,sappa deposits dated by ,schultz and ,tanner 7loc4 cit47 as mostly ,yarmouthian deposits4 ,geomys bisulcatus1 judging from the original description and ,hibbard's discussion of the cotypes 7#aied3ceg71 does not differ significantly from ,geomys bursarius4 ,however1 ,geomys bisulcatus is tentatively retained as a valid species4 ,based on the evidence cited above it seems unlikely that ,geomys bisulcatus occurred in pre-,irvingtonian times as often suggested in the literature4 ,the genus ,geomys has been identified in several faunas of ,illinoian age1 all from the ,great ,plains4 ,stephens 7#aifj3aifa7 reported the genus from the ,doby ,springs local fauna in ,harper ,county1 ,oklahoma1 and ,starrett 7#aief3aahh7 reported it from the ,berends local fauna in ,beaver ,county1 ,oklahoma4 ,schultz 7#aife3bdi7 assigned #ba isolated teeth1 including six incisors1 from ,butler ,springs local fauna 7considered by him to be late ,illinoian1 following the glacial maximum7 to ,geomys cf4 bursarius4 ,hibbard and ,taylor 7#aifj3afg7 reported a baculum tentatively identified as that of ,geomys from the early ,illinoian ,butler ,springs local fauna 7including the ,adams fauna7 of ,meade ,county1 ,kansas4 ,hibbard 7#aifc3bjf7 recorded the genus ,geomys from the ,mt4 ,scott local fauna 7late ,illinoian deposits7 of ,meade ,county1 ,kansas2 the specimens probably are referable to the living species bursarius4 ,from ,mc,pherson ,county1 ,kansas1 ,hibbard 7#aieb3g7 reported the genus ,geomys from the ,kentuck ,assemblage1 which he 7#aieh3be7 regarded as a composite of ,illinoian and ,sangamon species4 ,specific identification of the ,illinoian pocket gophers is uncertain1 primarily due to the fragmentary nature of the material4 ,on the basis of dental characters alone most specimens could be referred to ,g4 bursarius2 however the taxonomic status of ,g4 bisulcatus is in doubt1 and more complete material may indicate that the ,illinoian gophers are specifically distinct from the living species4 ,consequently1 most authors1 including myself1 have made no attempt to refer these specimens to species4 ,nevertheless1 the ,illinoian ,geomys from the ,great ,plains is more closely allied to the living species of ,geomys than it is to the earlier ,irvingtonian species4 ,geomys bursarius has been collected from a number of ,sangamon fossil sites on the ,great ,plains4 ,although specific identification of specimens of ,geomys from ,illinoian faunas is uncertain1 the ,great ,plains ,geomys from ,sangamon and later deposits probably is referable to the living species as ,hibbard and ,taylor 7#aifj3afe7 pointed out4 ,they found no difference between ,geomys recovered from the ,cragin ,quarry local fauna 7early ,sangamon7 of ,meade ,county1 ,kansas1 and the living species ,geomys bursarius4 ,isolated teeth of the same species were collected from the ,jinglebob local fauna of ,meade ,county1 ,kansas 7,hibbard1 #aiee;b3#bjf71 a fauna of the late ,sangamon4 ,hibbard 7#aidc3bdj7 also recorded the genus ,geomys 7referable to ,g4 bursarius7 from the ,rezabek local fauna of ,lincoln ,county1 ,kansas4 ,according to ,schultz et al4 7#aiea3f and table #a7 the genus ,geomys occurs in buried or fossil soils of ,sangamon age1 lying just above the ,loveland ,loess1 in ,nebraska4 ,no specific localities were given by them1 nor were any particular specimens mentioned4 ,dalquest reported ,geomys bursarius from two ,sangamon faunas in northern ,texas4 ,the species is represented in the ,ward ,quarry local fauna of ,cooke ,county1 ,texas 7#aifb;a3#db71 and the ,good ,creek local fauna of ,foard ,county1 ,texas 7#aifb;b3#ege74 ,geomys bursarius has been reported from ,wisconsin fossil deposits of the ,great ,plains and adjacent areas as follows3 ,jones local fauna1 ,meade ,county1 ,kansas 7,hibbard and ,taylor1 #aifj3fd-ff72 ,two ,creeks ,forest beds of the third interstadial soils formed between ,cary and ,mankato glaciations1 late ,wisconsin 7,schultz et al41 #aiea3h and table #a72 ,cita ,canyon local fauna in the northern part of the ,panhandle of ,texas 7,johnson and ,savage1 #aiee3ci72 ,howard ,ranch local fauna of ,hardeman ,county in northwestern ,texas 7,dalquest1 #aife3gj72 ,quitaque local fauna of ,motley ,county1 ,texas 7,dalquest1 #aifd3eja72 ,clear ,creek local fauna of ,denton ,county in north-central ,texas 7,slaughter and ,ritchie1 #aifc3abj72 ,ben ,franklin local fauna1 of late ,wisconsin beds along the ,north ,sulphur ,river in ,delta ,county1 ,,ne ,texas 7,slaughter and ,hoover1 #aifc3acg72 ,bulverde ,cave 7,hay1 #aibj3adj2 #aibd3bdg7 and ,friesenhahn ,cave 7,tamsitt1 #aieg3cba71 both in ,bexar ,county1 south-central ,texas2 ,alton1 ,illinois 7,hay1 #aibc3cch-cci72 ,wisconsin drift of ,illinois1 without mention of specific locality 7,bader and ,techter1 #aiei3agb72 ,wisconsin drift of southwestern ,wisconsin and northeastern ,iowa 7,hay1 op4 cit43#cdc72 ,wisconsin drift near ,galena1 ,illinois1 and mouth of ,platte ,river in eastern ,nebraska 7,leidy1 #ahfi3djf74 ,brown 7#aijh3aid7 described ,geomys parvidens from the ,conard ,fissure1 in northern ,arkansas4 ,hibbard 7#aieh3be7 concluded that the ,conard ,fissure fauna represents a glacial stage1 probably the ,illinoian1 and ,hibbard et al4 7#aife3eaj-eaa7 regarded the fauna as a composite including both ,irvingtonian and ,rancholabrean elements4 ,white and ,downs 7#aifa3ba7 considered ,g4 parvidens to be a subspecies of ,geomys bursarius4 ,the first ,pleistocene occurrence of ,geomys in the southeastern ,united ,states is from the ,reddick ,i deposits reported by ,gut and ,ray 7#aifc3cbe71 who found the remains of ,geomys pinetis among the fossils comprising the rodent beds of ,marion ,county1 ,florida4 ,gut and ,ray tentatively identified the beds as ,illinoian1 but ,kurten 7#aife3bai7 regarded the ,reddick ,i fauna as early ,sangamon4 ,simpson 7#aibh3b7 reported ,geomys floridanus pinetis from ,saber-tooth ,cave deposits of ,citrus ,county1 ,florida4 ,the ,saber-tooth ,cave 7or ,lecanto ,cave7 local fauna is considered by ,kurten 7op4 cit43#bai7 also to be a ,sangamon deposit4 ,geomys floridanus pinetis was reported from the ,seminole ,field deposits by ,simpson 7#aibi3efc72 both ,simpson and ,kurten 7op4 cit43#bba7 agreed that the ,seminole ,field fauna is mainly late ,wisconsin1 although sub-,recent fossils occur at the tops of the beds4 ,ray 7#aieh3dcj7 collected remains of ,geomys pinetis from the ,melbourne ,bone ,bed of ,brevard ,county1 ,florida4 ,the ,melbourne local fauna is considered to be from ,wisconsin deposits by ,kurten 7op4 cit43#bbj74 ,the eastern species of ,geomys were probably derived from ,great ,plains stock that reached the southeastern ,coastal ,plains in early ,rancholabrean 7,illinoian7 time4 ,presently there is no contact between the eastern and western populations of the genus1 and it is assumed that disjunction occurred as a result of ,wisconsin glaciation4 ,it is interesting to note that the genus ,thomomys occurred in this region at approximately the same time2 both genera occur in ,saber-tooth ,cave deposits4 ,pappogeomys ,the genus ,pappogeomys is not known from ,pleistocene deposits older than the ,wisconsin glaciation1 but a pre-,pleistocene occurrence in the ,benson beds of ,arizona 7see discussion of the ,pliocene above7 shows that ,pappogeomys had been differentiated by late ,pliocene time4 ,the absence of ,pappogeomys1 beginning in the early ,pleistocene and continuing well into the late ,pleistocene1 is attributed to the southern distribution of the genus1 where its range probably was centered on the ,central ,plateau of ,mxico4 ,the paucity of early and middle ,pleistocene deposits from this critical region prevents any definite statements about phyletic development within the genus4 ,all of the late ,pleistocene records pertain to the subgenus ,cratogeomys 7long in use as a generic name but in the present paper reduced to subgeneric rank in the genus ,pappogeomys74 ,schultz and ,howard 7#aice3bhj7 found ,cratogeomys ,pappogeomys castanops in ,burnett ,cave in the ,guadalupe ,mountains of south-central ,new ,mexico4 ,the ,burnett deposits are probably late ,wisconsin 7see ,schultz and ,tanner1 #aieg3ge1 for discussion of the age of these deposits based on carbon-#ad tests74 ,these writers 7loc4 cit47 also referred the mandible of a small pocket gopher to the genus ,pappogeomys subgenus ,pappogeomys4 ,however1 neither genera nor subgenera of the tribe ,geomyini can be distinguished on the basis of their inferior dentitions4 ,judging from the distribution of the modern geomyines1 it seems unlikely that the subgenus ,pappogeomys has occurred beyond its present range in the late ,pleistocene2 therefore the small mandible is most likely that of a young individual of ,pappogeomys castanops4 ,russell 7#aifj3edc7 referred specimens collected at ,san ,josecito ,cave in ,nuevo ,len1 ,mxico1 to the group of small subspecies ,cratogeomys ,pappogeomys castanops4 ,also1 ,russell 7loc4 cit47 identified a rostral fragment as of the genus ,cratogeomys subgenus ,cratogeomys although the fragment had a combination of features different than in any named species of the genus2 he did not name the fragment as a new species1 preferring to wait for additional material that could clarify its taxonomic relationships4 ,hibbard 7#aiee;a3#eb-ec7 identified ,cratogeomys ,pappogeomys tylorhinus from the ,becerra ,superior deposits in the valley of ,tequixquic in the northern part of the state of ,mxico4 ,the ,wisconsin age of these beds suggests an earlier ,pleistocene derivation of the gymnurus-group of species4 ,several specimens of the subgenus ,cratogeomys have been reported from beds of latest ,wisconsin 7certainly after the glacial maximum7 or post-,wisconsin age4 ,gilmore 7#aidg3aeh7 found fossil remains of ,cratogeomys ,pappogeomys castanops commonly in ,quaternary cave deposits on the mountain slopes in the vicinity of ,cuatro ,cinegas1 in central ,coahuila4 ,these deposits actually may be of post-,wisconsin origin 7see discussion above74 ,alvarez 7#aifd3h7 obtained fragments of ,cratogeomys ,pappogeomys tylorhinus from sub-,recent deposits of ,capa ,,iii in the ,cueva ,la ,nopalera in southwestern ,hidalgo1 ,mxico4 ,pappogeomys merriami lives in the area today4 ,mayer-,oakes 7#aiei3cgc7 reported remains of ,cratogeomys ,pappogeomys merriami from levels eight and eleven of the excavations at ,el ,risco ,,ii1 in the northern part of ,mexico ,city4 ,the ages of these deposits are unknown to me1 but they probably are no older than late ,wisconsin with most of the beds dating from the post-,wisconsin4 ,orthogeomys ,this genus is not known from the ,pleistocene1 except for its occurrence in the ,san ,josecito cave deposits of southwestern ,nuevo ,len1 ,mxico 7,russell1 #aifj3edd74 ,although ,orthogeomys does not occur in the immediate vicinity of the cave at the present time1 the northern limits of its range is nearby in southern ,tamaulipas4 ,the ,orthogeomys from ,san ,josecito ,cave differs from living species1 and has been named ,heterogeomys ,orthogeomys onerosus ,russell 7loc4 cit471 and is evidently referable to the subgenus ,heterogeomys4 ,as mentioned before1 the ,san ,josecito ,cave local fauna represents deposits of ,wisconsin glaciation4 ,,history ,,of ,,classification ,the account of the ,tucan or ,indian mole by ,hernandez 7sometimes listed as ,fernandez7 in #afea probably is the earliest published one of a geomyid 7see ,merriam1 #ahie3bja2 ,coues1 #ahgg3fjg-fjh74 ,linnaeus in #ageh did not mention geomyids4 ,in #aggb1 ,kerr described ,hernandez's ,tucan under the name ,sorex mexicana on the basis of ,hernandez's account without having seen any specimens4 ,lichtenstein in #ahbg applied the technical name ,ascomys mexicana to three specimens collected by ,deppe from unknown localities on the tableland of ,mxico4 ,merriam 7loc4 cit47 pointed out that the name mexicanus of ,lichtenstein in #ahbg is a nomen nudum1 and that it is preoccupied by mexicanus used by ,kerr in #agib4 ,the latter can not be technically identified with any particular species of geomyid4 ,bartram in #agia wrote of the pocket gopher of ,florida1 without formally describing it4 ,the first available technical name is ,mus bursarius of ,shaw in #ahjj4 ,rafinesque in #ahag proposed the first generic names for the geomyids when he described ,geomys and ,diplostoma4 ,in #ahci1 ,waterhouse referred the genus ,geomys to his family ,arvicolidae1 considered by him to be a subgroup of muroids4 ,in #ahda1 he suggested that ,geomys was related to ,bathyergus and ,spalax4 ,waterhouse in #ahdh 7p4 #h7 treated the pocket gophers as a subgroup of rodents under the group name ,saccomyina1 in which he included the genera ,heteromys1 ,saccomys1 ,perognathus1 and ,dipodomys4 ,hence1 ,waterhouse was the first to recognize the relationship between the heteromyids and geomyids4 ,in the next year ,gervais erected the family ,pseudostomidae for a group of specialized squirrels to include ,geomys and ,thomomys and the same genera 7at least in part7 of heteromyids that ,waterhouse classified in the family ,saccomyina4 ,in #ahci the name ,thomomys was proposed by ,maximilian 7,wied-,neuwied74 ,all of the generic names previously proposed for pocket gophers were considered by subsequent authors to be synonyms of ,geomys4 ,a third family name1 ,sciurospalacoides1 was proposed by ,brandt 7#ahee3ahh7 who referred ,geomys and ,thomomys to that family4 ,he placed his new family phylogenetically between the family ,sciuridae and the family ,spalacoides 7a group in which ,brandt included the genera ,spalax1 ,sipheus1 and ,ellobius74 ,brandt took exception to the classification of ,waterhouse 7#ahdh71 who united the geomyids and heteromyids in one family4 ,brandt placed the heteromyid genera in other groups3 ,perognathus in the ,muridae1 and ,macrocolus ,dipodomys in the ,macrolini1 a subfamily of the family ,dipodoides4 ,modern classification of the pocket gophers begins with ,baird in #aheh4 ,the important classifications are summarized in ,table #a2 a few that do not depart essentially from those listed have been omitted owing to limited space for the tabular arrangement1 but are discussed in the following account4 ,baird probably was strongly influenced by the arrangement proposed by ,waterhouse in #ahdh1 but was opposed to separating geomyids from heteromyids as was done by ,brandt4 ,baird was convinced of the close relationship of the geomyids and heteromyids1 and referred both groups to one family1 the ,saccomyidae1 as ,waterhouse had done earlier4 ,in order to recognize the morphological specializations he used two subfamilies1 ,geomyinae and the ,saccomyinae4 ,in the #bj years that followed1 some authors followed ,brandt and others followed ,baird4 ,gill1 in #ahgb 7p4 #ga71 proposed a classification essentially like ,baird's of #aheh1 but ,gill raised ,baird's subfamilies to the rank of family 7see ,table #a74 ,in referring all pocket gophers to the ,geomyidae1 ,gill used that name as a family term for the first time4 ,also he established the superfamily ,saccomyoidea to include his two families1 ,geomyidae and ,saccomyidae2 therefore1 the ,saccomyoidea was equivalent to the group ,saccomyina of ,waterhouse 7#ahdh7 and the ,saccomyidae of ,baird 7#aheh74 ,coues 7#ahgg71 in his classic monograph of the ,geomyidae followed the arrangement proposed by ,gill in treating the pocket gophers as a family4 ,alston in #ahgf proposed another classification based on ,baird 7#aheh71 with two subfamilies1 the ,geomyinae and the ,heteromyinae1 united together in the family ,geomyidae2 thus1 he recognized that the genus ,saccomys ,frdric ,cuvier1 #ahbc1 was a synonym of ,heteromys ,desmarest1 #ahag1 as had been pointed out by ,gray 7#ahfh3bja7 and ,peters 7#ahgd3cef74 ,coues 7#ahgg3dhg-dij7 acknowledged the invalidity of the genus ,saccomys1 but refused to give up the name in supergeneric classification4 ,winge1 first in #ahhg and subsequently in #aibd1 classified the geomyids and heteromyids together in the family ,saccomyidae as did ,baird in #aheh1 and like ,coues1 ,winge too ignored the synonymy of ,saccomys with ,heteromys and insisted on retaining the technical terms ,saccomyidae and ,saccomyini4 ,up to the time of ,merriam's classic revision of the ,recent ,geomyidae in #ahie all the known species of living pocket gophers were referred to two genera1 ,geomys and ,thomomys4 ,merriam described much new material1 especially from ,mxico and ,central ,america1 and proposed seven new genera 7see ,table #a74 ,his complete and detailed study of the dentitions and osteology of the skull remains today as the definitive work on this subject1 and is the point where most studies of the ,geomyidae must begin4 ,his treatment of the ,recent genera survived for #eb years without change until ,hooper 7#aidf3cig7 arranged ,platygeomys as a synonym of ,cratogeomys4 ,however1 ,merriam's genera have been recognized in all subsequent classifications except for the current review 7see ,table #a74 ,cope described the first known fossil geomyids in #ahgh1 and published an excellent review of the two genera1 ,pleurolicus and ,entoptycus1 in #ahhd 7pp4 #hee-hgj1 pl4 #fd1 figs4 #a-i74 ,both genera were recovered from the ,john ,day ,miocene deposits of ,oregon4 ,cope did not propose a new systematic arrangement of these geomyids1 but referred them to the family ,saccomyidae and mentioned that the ,saccomyidae was equivalent to the family ,geomyidae of ,alston4 ,winge1 in #ahhg1 followed ,cope in referring ,pleurolicus and ,entoptycus to the ,saccomyidae along with the living genera ,thomomys and ,geomys4 ,miller and ,gidley 7#aiah71 in their synopsis of the supergeneric groups of rodents1 proposed a new subfamily1 ,entoptychinae1 to include the divergent ,miocene pocket gophers4 ,miller and ,gidley also revived the old subfamily ,geomyinae of ,baird 7#aheh71 but restricted its application to the modern pocket gophers and their immediate ancestors4 ,in #aicf1 ,a4 ,e4 ,wood revised the taxa of the subfamily ,entoptychinae1 and described the first ,miocene genus1 ,dikkomys1 of the ,geomyinae4 ,he followed the supergeneric classification of ,miller and ,gidley 7#aiah74 ,the recent classifications of ,simpson 7#aide7 and ,wood 7#aiee7 have combined the classifications of ,merriam 7#ahie7 and ,wood 7#aicf74 ,wood 7#aiee7 brought up to date the list of genera1 including those that were described after the publication of ,simpson's classification 7#aide74 ,in ,table #a1 the list of genera is principally from ,simpson 7#aide7 but generic names used by ,wood 7#aiee7 are included4 ,this is the currently accepted classification4 ,the new classification proposed in this paper 7see ,table #a7 includes three tribes proposed as vertical units2 they are intended to stress the phyletic trends in the known evolutionary sequences by placing immediate ancestors together with their descendants4 ,pliogeomys is placed in the same tribe 7,geomyini7 as ,zygogeomys1 ,geomys1 ,orthogeomys1 and ,pappogeomys4 ,that tribe includes the most specialized ,geomyinae4 ,zygogeomys1 ,geomys1 ,orthogeomys1 and ,pappogeomys are lineages resulting from a ,pleistocene radiation in which all the lineages diverged from a common ,pliocene ancestor4 ,the radiation of the ,geomyini was well under way by the close of the late ,pliocene4 ,although ,pliogeomys may not be the actual ancestor1 it closely resembles the primitive morphotype4 ,,table #a4--;,history of the classification of the ,superfamily ,geomyoidea ,baird #aheh ,gill #ahgb ,winge #ahhg ,merriam #ahie ,coues #ahgg and #aibd ,ellerman #aidj ---------------------------------------- ----------------------- ,family ,family ,family ,family ,saccomyidae ,geomyidae ,saccomyidae ,geomyidae ---------------------------------------- ----------------------- ,subfamily ,group ,geomyinae ,geomyini -- -- -- -- -- -- -- -- -- ---- -- -- -- -- -- -- -- -- -- -- - ,thomomys ,thomomys ,thomomys ,thomomys ,zygogeomys ,geomys ,geomys ,geomys ,geomys ,orthogeomys ,heterogeomys ,macrogeomys ,pappogeomys ,cratogeomys ,platygeomys -- -- -- -- -- -- -- -- -- ---- -- -- -- -- -- -- -- -- -- -- - 99,pleurolicus 99,entoptychus ---------------------------------------- ----------------------- ,group ,gymnoptychine9999 ,gymnoptychus ---------------------------------------- ----------------------- ,subfamily ,family ,group ,saccomyinae ,saccomyidae ,saccomyini ---------------------------------------- -------------------- ,wood #aice ,simpson #aide ,names used in ,wood #aicf ,wood #aiee present paper ---------------------------------------- --------------------- ,family ,family ,family ,geomyidae ,geomyidae ,geomyidae ---------------------------------------- --------------------- ,subfamily ,subfamily ,subfamily ,geomyinae ,geomyinae ,geomyinae -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- - ,tribe ,dikkomyini 99,dikkomys 99,dikkomys 99,dikkomys 99,pliosaccomys 99,pliosaccomys ,tribe ,thomomyini 99,pleisothomomys 99,pleisothomomys ,thomomys ,thomomys ,thomomys ,tribe ,geomyini 99,pliogeomys 99,pliogeomys ,zygogeomys ,zygogeomys 99,nerterogeomys ,zygogeomys ,geomys ,geomys 99,parageomys ,geomys ,orthogeomys ,orthogeomys ,heterogeomys ,heterogeomys ,orthogeomys ,macrogeomys ,macrogeomys ,pappogeomys ,pappogeomys ,cratogeomys ,cratogeomys ,pappogeomys ,platygeomys ,platygeomys -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- - ,subfamily ,subfamily ,subfamily ,entoptychinae ,entoptychinae ,entoptychinae 99,pleurolicus 99,pleurolicus 99,pleurolicus 99,gregorymys 99,gregorymys 99,gregorymys 99,grangerimus 99,grangerimus 99,grangerimus 99,entoptychus 99,entoptychus 99,entoptychus ---------------------------------------- --------------------- ,geomyidae ,geomyidae incertae sedis incertae sedis 99,gidleumys 99,diplolophus 99,diplolophus 99,griphomys 99,griphomys ---------------------------------------- --------------------- ,family ,family ,family ,heteromyidae ,heteromyidae ,heteromyidae ---------------------------------------- --------------------- 99 ,denotes extinct genera4 9999 ,winge included in his family ,saccomyidae the group ,gymnoptychine and the contained genus ,gymnoptychus ,cope1 #ahgc1 which genus currently is placed in the family ,eomyidae4 ,the type of ,gymnoptychus ,cope1 #ahgc1 is synonymous with ,ischyromys ,leidy1 #ahef1 and the valid name for the genus is ,adjidaumo ,hay1 #ahii4 ,pliosaccomys1 on the other hand1 represents the terminal stages of a long trend that began with the ,dikkomys-like ,geomyinae of the early ,miocene4 ,in this lineage1 the rate of evolution in the dentition and the skull was slow2 therefore1 the differences between early ,miocene 7,dikkomys7 and middle ,pliocene 7,pliosaccomys7 are not great and the two are united into the tribe ,dikkomyini4 ,the ,dikkomyini is the ancestral geomyinen trunk from which the modern groups have diverged4 ,the ,pliocene ancestor of ,thomomys is unknown but probably resembled ,pliosaccomys1 with which it may have been a contemporary4 ,thomomys is the least specialized of the modern ,geomyinae1 and1 consequently1 shows the most resemblance to the ancestral tribe4 ,the specializations of ,thomomys1 however1 clearly preclude its reference to the tribe ,dikkomyini2 therefore1 it is set apart in the monotypic tribe ,thomomyini4 ,that tribe has not undergone an adaptive radiation comparable to that of the tribe ,geomyini or that of the ,entoptychinae in the early ,miocene4 ,here1 for the first time1 ,thomomys is set apart in classification from the other living pocket gophers4 ,merriam's genera ,orthogeomys1 ,heterogeomys1 and ,macrogeomys are closely related4 ,each of these taxa is retained as a subgenus of a single genus1 ,orthogeomys4 ,some species of ,macrogeomys seem to be more closely allied to the subgenus ,orthogeomys and others to the subgenus ,heterogeomys4 ,a revision of the genus is needed2 it might show that the currently recognized subgenera are artificial1 and that a different arrangement of the species would more clearly express their evolutionary relationships4 ,the subgenus ,heterogeomys seems to be the most nearly uniform of the subgenera1 and it is the least specialized4 ,radiation within the genus may have begun relatively recently1 but the many special adaptations for tropical environments suggest that the genus has been in the ,neotropical ,zone a long time4 ,therefore1 discovery of an early dichotomy from the common ancestral stock of the tribe would come as no surprise4 ,nerterogeomys ,gazin here is arranged as a junior synonym of ,zygogeomys4 ,both are less specialized than any of the other ,geomyini1 except ,pliogeomys4 ,the single living species 7,zygogeomys tricopus7 is obviously a relic4 ,its range is small4 ,the two subspecies differ only in minor features4 ,the living species does have a few unique characteristics1 only to be expected in the surviving species of a long phyletic lineage4 ,some of these are specializations4 ,otherwise1 ,zygogeomys and ,nerterogeomys are closely related and the latter is best placed as a synonym of the former4 ,both are admittedly closely related to ,geomys4 ,zygogeomys and ,geomys share several characters1 particularly primitive ones2 there is considerable parallelism1 especially marked in ,irvingtonian species of ,geomys4 ,nevertheless1 ,geomys is more specialized1 particularly in the dentition1 and it has developed some ,pappogeomys-like specializations4 ,zygogeomys has retained more of the primitive characters of the tribe4 ,a strong case could be made for recognizing only one genus1 ,geomys1 containing ,zygogeomys as one of two subgenera4 ,nevertheless1 the characters separating ,zygogeomys and ,geomys are of considerable importance and ,i consider the two kinds to be distinct genera4 ,the species of ,geomys1 both living and extinct1 form a distinct and well-marked group4 ,the genus is less primitive in most respects than ,zygogeomys and ,orthogeomys and it is less specialized than ,pappogeomys1 excluding the ancestral stock 7subgenus ,pappogeomys74 ,some specimens of species of ,irvingtonian age 7,geomys tobinensis and ,geomys garbanii1 especially the former7 retain primitive enamel plates as does ,zygogeomys2 but this is true of only a small percentage of the individuals4 ,also the adult dental pattern developed somewhat later in ontogeny in these middle ,pleistocene species of ,geomys than in either ,recent or late ,pliocene and early ,pleistocene representatives 7,geomys paenebursarius1 ,geomys quinni7 of the genus4 ,whether these features represent a stage in the evolution of the late ,pleistocene and ,recent species or a terminal stage in members of a sterile and primitive branch of the main line of evolution of ,geomys is uncertain4 ,at present ,i favor the latter explanation1 and view ,g4 paenebursarius and ,g4 quinni as early progressive species that evolved dental specializations that were maintained in the main line of phylogeny4 ,hibbard proposed the generic name ,parageomys 7#aidd3ee71 but later regarded it as a subgenus of ,geomys 7#aief3ahb7 that includes those species retaining continuous enamel bands until relatively late in ontogeny2 no other differences have been noted4 ,when the early phylogeny of ,geomys is better understood1 ,parageomys may serve as a subgeneric taxon in which the primitive species of ,geomys can be grouped1 but as of now ,parageomys is arranged as a synonym of ,geomys4 ,pappogeomys and ,cratogeomys also form a natural group4 ,their close relationship is best reflected in formal taxonomy by including them in the same genus4 ,their dissimilarities are of the sort that separate a primitive ancestral lineage from a divergent and progressively more specialized assemblage4 ,the fossil record is inadequate1 and ,i can only speculate that ,cratogeomys diverged from primitive ,pappogeomys-stock in the earlier ,pleistocene1 at least before the end of the ,irvingtonian4 ,cratogeomys probably originated on the ,mexican ,plateau and probably underwent its subsequent evolution there4 ,the living species of the subgenus ,pappogeomys are evidently relics of the ancestral stock of the genus4 ,hooper 7#aidf3cig71 ,i think correctly1 considered ,platygeomys as congeneric with ,cratogeomys1 although the highest degree of specialization of the genus is attained in those species formerly classed in the genus ,platygeomys4 ,even so1 in my opinion1 the differences are insufficient to warrant even subgeneric recognition4 ,,classification ,family ,,geomyidae ,gill1 #ahgb ,rodents of the superfamily ,geomyoidea specialized for completely fossorial life 7early ,pliocene to ,recent72 specialized earlier 7late8 ,oligocene and early ,miocene7 for semi-fossorial habits2 body thickset1 fusiform without apparent neck 7in modern geomyids72 legs short2 forelegs especially stout2 eyes and ears small 7pinna reduced to inconspicuous crest concealed beneath pelage72 tail tactile1 shorter than head and body2 lips closing behind incisors2 cheek pouches external1 fur-lined2 baculum rodlike1 arched1 having expanded quadriform platelike base2 pelage long1 soft without underfur1 covering body in thick coat 7in some species of ,orthogeomys scant1 harsh or scattered bristles72 color varying from pale tints of buffy 7almost white7 to metallic black4 ,skull thick-walled1 massive1 angular1 relatively broad1 and flattened2 distinctly murine form1 but having zygomasseteric structure of advanced sciuromorphs1 including small infraorbital canal 7that transmits no part of masseter muscle7 and well-developed1 broad zygomatic plate2 zygomata massive and widely flaring1 jugals stout2 rostrum robust1 relatively broad and deep1 and without evidence of transverse canal 7as in ,heteromyidae72 anterior projection of nasals only slightly exceeding that of upper incisors2 interorbital region usually constricted1 narrower than rostrum2 anterior opening of infraorbital canal far forward on side of rostrum1 about half way between zygomatic plate and upper incisor and just behind premaxillary-maxillary suture1 its opening countersunk in oblique sulcus 7for protection from muscle contraction72 postorbital process lacking1 except for rudimentary knoblike projection in subgenus ,macrogeomys2 palate relatively narrow1 its deeply sculptured surface sloping steeply downward posteriorly causing region supporting maxillary tooth-row to be markedly depressed2 palatine bone reduced1 forming1 on two abruptly different levels1 posterior margin of hard palate behind tooth-rows2 parietals compressed and narrow1 and most of cerebral cavity roofed by squamosals 7in some species squamosals overlap lateral parts of parietals72 tympanic bullae completely inferior in position and fully ossified1 external meatus being developed laterally as elongated tube2 mastoid not inflated1 but broadly exposed at posterolateral margin of the skull2 occiput large1 its surface usually rugose1 and paroccipital processes large and flangelike1 at least in advanced groups 7early ,pliocene to ,recent72 ramus relatively short and stout1 having distinct crest and ridges for muscle attachments2 coronoid process well developed1 erect2 articular condyle prominent2 angular process prominent1 reflected laterally1 and in modern groups lateral extension protruding from posterior border of ramus nearly at right angle2 capsule for root of lower incisor1 prominent between angular process and articular condyle4 ,anterior surface of incisors broad and flat1 always smooth on lower teeth1 but either smooth or grooved on upper teeth depending on taxon2 cheek teeth hypsodont1 becoming progressively higher crowned in modern groups1 rooted in primitive groups 7late8 ,oligocene to middle ,pliocene71 rootless and ever-growing in modern groups 7late ,pliocene to ,recent72 upper and lower premolars persistently bicolumnar2 upper and lower molars bicolumnar only in primitive groups 7late8 ,oligocene and early ,miocene71 becoming progressively monocolumnar in advanced groups 7early ,pliocene to ,recent71 primitive bicolumnar pattern being retained on occlusal surface only in early stages of ontogeny and in third molar throughout life2 enamel pattern of occlusal surface of cheek teeth based on sextituberculate prototype 7see ,wood and ,wilson1 #aicf3chh-cia71 having cusps arranged in two transverse rows of three cusps each1 excepting three anterior cusps of premolars that are arranged in trefoil1 especially on p#d 7sometimes only one or two1 rather than three1 cusps develop in a particular set1 especially in p#d71 conules absent2 protostyle and endostyle in upper teeth and protostylid and hypostylid in lower teeth formed from cingulum2 cusps of each row uniting with wear into transverse enamel lophs 7or lophids71 each tooth having two lophs1 one on anterior column1 protoloph and protolophid1 and one on posterior column1 hypoloph and hypolophid1 that unite with additional wear forming continuous enamel band2 enamel lacking on sides of each column in advanced lineages1 thereby restricting enamel to anterior and posterior walls2 with extreme reduction1 posterior plates of upper teeth and1 more commonly1 anterior plates of lower molars1 missing4 ,dental formula3 #a_/a1 #j_/j1 #a_/a1 #c_/c4 ,key to the ,subfamilies of ,geomyidae ,a ,angular process of ramus mostly below alveolar level of mandibular tooth-row2 pattern of premolar like that of molars1 consisting of two subequal crests united at one or both margins of tooth2 molars persistently bicolumnar2 molariform teeth always rooted4 ,subfamily ,entoptychinae p4 #eac ,a ,angular process of ramus mostly above level of mandibular tooth-row2 pattern of permolar unlike that of molars1 consisting of two prisms differing in size and united at their mid-points but never at either margin2 molars progressively monocolumnar1 except for early ,miocene forms2 molariform teeth rooted only in primitive genera 7late8 ,oligocene to middle ,pliocene71 and rootless and ever-growing in later genera 7late ,pliocene to ,recent74 ,subfamily ,geomyinae p4 #ead ,subfamily ,,entoptychinae ,miller and ,gidley1 #aiah ,anterior face of upper incisor usually smooth1 sometimes bearing faint groove in center or near medial margin of tooth1 at least in ,gregorymys2 cheek teeth hypsodont1 medium to high crowned1 and rooted in all but ,entoptychus 7has rootless1 ever-growing teeth72 cheek teeth identical in form1 premolars resembling molars and lower cheek teeth mirror images of upper teeth2 crowns biprismatic1 having two columns joined at edge of protomeres 7for description of term1 see discussion of primitive morphotype on page #ecg7 and with persistent lateral fissure between them2 lateral re-entrant fold deep1 penetrating at least half width of crown1 from external side in upper teeth and internal side in lower teeth 7in specialized genus ,entoptychus lophs1 upon additional wear1 join also at edge of parameres1 thus uniting columns at both ends and thereby enclosing interior part of lateral fissure as a transverse fossette in center of tooth72 enamel investment of prisms usually complete1 including inflection bordering re-entrant folds1 occlusal pattern becoming interrupted with wear only in ,entoptychus1 where enamel disappears first from sides of crowns 7following union of anterior and posterior columns at both sides7 and later1 in final stages of attrition1 from anterior wall of lower molars and posterior wall of upper molars4 ,maxillary bone without pronounced vertical depth in part supporting cheek teeth1 its inferior border only slightly lower than inferior border of premaxillary and alveolar lips of molariform teeth consequently approximately level with1 or slightly below1 alveolar lip of upper incisor2 squamosal without lateral expansion1 therefore1 meatal tube of auditory bulla separated from zygomatic process of squamosal by deep1 well-developed postglenoid notch2 angular part of mandible below alveolar level of mandibular cheek teeth2 angular process only slightly reflected laterally2 coronoid process low1 tip only slightly above condyle4 ,for information concerning the structure and relationships of the known genera1 and for accounts of species1 see ,wood 7#aicf74 ,a list of the named genera in order of specialization is as follows3 99,pleurolicus ,cope1 #ahgh4 ,proc4 ,amer4 ,phil4 ,soc41 #ah3ff4 99,gregorymys ,wood1 #aicf4 ,amer4 ,mus4 ,novit41 #hff3i4 99,grangerimus ,wood1 #aicf4 ,amer4 ,mus4 ,novit41 #hff3ac4 99,entoptychus ,cope1 #ahgh4 ,proc4 ,amer4 ,phil4 ,soc41 #ah3fd4 ,five new species have been described since ,wood's 7#aicf7 revision4 ,they are3 ,pleurolicus clasoni ,mac,donald 7#aifc3ahj72 ,gregorymys kayi ,wood 7#aiej3cce72 ,gregorymys montanensis ,hibbard and ,keenmon 7#aiej3aih72 ,grangerimus dakotensis ,mac,donald 7#aifc3ahb72 ,grangerimus sellardsi ,hibbard and ,wilson 7#aiej3fbc74 ,subfamily ,,geomyinae ,baird1 #aheh ,anterior face of upper incisor primitively smooth1 grooves consistently developed only in one modern lineage 7,geomyini72 cheek teeth hypsodont1 primitively rooted and having crown of medium height 7late ,oligocene to middle ,pliocene71 being higher crowned1 rootless and ever-growing in modern lineages 7late ,pliocene to ,recent72 primitively crowns of cheek teeth biprismatic1 having two columns joined at mid-points by narrow isthmus and entire crown sheathed in continuous band of enamel2 premolars retaining primitive biprismatic form1 anterior and posterior columns never uniting at edge of protomeres or parameres1 and with both lateral re-entrant folds persistent throughout life2 primitive biprismatic pattern becoming decidedly modified in molars 7except in ,m#c71 having two prisms progressively uniting into one column by reduction and loss of lateral inflections1 primitive biprismatic patterns being retained only in early stages of ontogeny2 third upper molars retaining1 at least partially1 primitive bicolumnar pattern 7except in ,thomomyini71 with relatively broad isthmus and horizontally shallow re-entrant folds1 lingual fold sometimes wanting2 enamel pattern becoming discontinuous 7late ,pliocene to ,recent7 owing to loss of enamel from sides of each column2 remaining enamel restricted to anterior and posterior plates1 or cutting blades1 and enamel bordering lateral inflections in premolars 7considering both sides together1 these plates constitute essentially two transverse cutting blades72 enamel pattern of ,m#c varying1 depending on taxon2 with specialization1 anterior plates of lower molars and posterior plates of upper premolar and molars may be reduced or lost2 except in primitive species 7early ,miocene71 no enamel fossettes retained in adult dentitions4 ,maxillary bone having pronounced vertical depth in part supporting cheek teeth1 inferior border arching downward well below inferior border of premaxillary2 consequently1 alveolar lips of molariform teeth decidedly below level of alveolar lip of upper incisor2 squamosal with marked lateral expansion at expense of postglenoid notch2 notch compressed and reduced between meatal tube of auditory bulla and zygomatic process of squamosal2 angular part of mandible mostly above alveolar level of mandibular cheek teeth2 angular process reflected laterally at right angles to axis of ramus and developed into heavy knoblike projection2 coronoid process well developed1 tip decidedly higher than condyle2 fossorial specializations remarkably well developed in advanced lineages1 degree of specialization of primitive ,miocene species unknown but probably only semi-fossorial as in ,entoptychinae4 ,key to the ,tribes of the ,geomyinae ,a ,enamel investment complete and uninterrupted1 even in final 7adult7 stages of wear2 cheek teeth rooted1 with crowns of medium height2 third lower molar biprismatic1 the two columns separated by inner and outer re-entrant folds as in lower premolar4 ,tribe ,dikkomyini p4 #eae ,a ,enamel investment incomplete and discontinuous1 reduced1 at least in final 7adult7 stages of wear1 to interrupted enamel plates2 cheek teeth rootless and ever-growing 7except in extinct genus ,pliogeomys71 crowns of maximum height2 third lower molar monoprismatic1 without trace of inner and outer re-entrant folds as in first and second lower molars4 ,b ,upper incisors smooth1 occasionally with a fine indistinct groove near inner margin of tooth2 form of third upper molar same as ,m#a and ,m#b1 monoprismatic1 anteroposteriorly compressed1 and having transverse enamel plates on both anterior and posterior faces1 and without suggestion of either labial or lingual re-entrant folds2 basitemporal fossa absent 7except for a shallow depression in one ,recent species1 ,t4 townsendii72 forefoot small and narrow with claws not elongated for digging4 ,tribe ,thomomyini p4 #eah ,b ,upper incisors grooved1 bearing either one or two sulci2 form of third upper molar distinctly different from ,m#a and ,m#b1 fully or partially biprismatic 7with a few exceptions discussed beyond71 without marked anteroposterior compression 7either subtriangular1 elongated1 suborbicular or quadriform in cross-section1 but not elliptical as in ,m#a and ,m#b71 and having typical transverse anterior plate and two lateral plates 7varying in their development1 depending on taxa71 but no posterior plate1 and with lateral re-entrant folds usually developed1 especially labial inflection 7although sometimes minute in a few species1 as described beyond72 basitemporal fossa well-developed1 although occasionally shallow or absent 7primitive species of ,zygogeomys72 forefoot large and broad1 with elongated claws for digging4 ,tribe ,geomyini p4 #eba ,tribe ,,dikkomyini1 new tribe ,genotype4--,dikkomys ,wood1 #aicf4 ,chronologic and geographic range4--,early to ,middle ,pliocene 7early ,arikareean to mid-,hemphillian7 in western ,united ,states4 ,known from ,miocene fossil sites in ,montana1 ,south ,dakota1 and ,nebraska and ,pliocene sites in ,south ,dakota1 ,oregon1 ,nevada1 and southern ,california4 ,for precise localities see accounts of ,dikkomys and ,pliosaccomys beyond4 ,diagnosis4--,small ,geomyinae2 lacking specializations of more advanced tribes2 upper incisors smooth1 at least in ,pliosaccomys2 molariform teeth always rooted and having crowns of medium height2 enamel investment of cheek teeth complete and uninterrupted in all stages of wear2 crowns of molars primitively biprismatic1 having two columns united at mid-points1 thus forming narrow isthmus separating lateral re-entrant folds as in premolars1 and1 with wear1 also uniting secondarily at protomeres 7with exception of third lower molars71 consequently1 isolating remnant of that inflection as shallow fossette 7columns uniting first at protomeres in ,pliosaccomys72 anterior and posterior columns of first and second molars1 both above and below1 becoming progressively united into one column in advanced ,dikkomyini 7early and middle ,pliocene71 but m#c 7,m#c unknown7 retaining primitive biprismatic pattern1 with columns joined at centers but never at protomeres 7for details of dentition see generic accounts72 mandible stout1 its angle mostly above mandibular tooth-row2 masseteric ridge low2 basitemporal fossa barely discernable in some fragments of ,pliosaccomys2 postcranial skeleton unknown4 ,key to the ,genera of the ,tribe ,dikkomyini ,a ,molars biprismatic throughout life2 anterior and posterior lophs of first and second molars in pre-final stages of wear uniting first at their mid-points and later at edge of protomeres2 anterior lophid of lower premolar having distinct anteroexternal inflection4 ,genus ,dikkomys p4 #eaf ,a' ,first and second molars becoming monoprismatic in final 7adult87 stages of wear1 biprismatic only in pre-final stages of wear2 third molars persistently biprismatic2 anterior and posterior lophs of first and second molars uniting first at edge of protomeres2 anterior lophid of lower premolar lacking anteroexternal inflection4 ,genus ,pliosaccomys p4 #eag ,genus ,dikkomys ,wood #aicf4 ,dikkomys ,wood1 ,amer4 ,mus4 ,novit41 #hff3bf1 ,july #b4 ,type4--,dikkomys matthewi ,wood1 #aicf1 from ,lower ,harrison deposits near ,agate1 ,sioux ,county1 ,nebraska4 ,chronologic range4--,early ,miocene1 from early ,arikareean 7,lower ,harrison local fauna of ,nebraska7 to middle ,miocene1 late ,hemingfordian 7,upper ,rosebud local fauna1 ,south ,dakota1 and the ,deep ,river ,formation1 ,montana74 ,according to ,mac,donald 7#aifc3adi-aej71 the ,upper ,rosebud is middle ,miocene rather than early ,miocene4 ,description4--,size small1 about as in small kinds of ,thomomys2 known only from fragmentary mandible1 including molariform dentition in place1 and isolated cheek teeth1 including ,m#a 7see ,wood1 #aicf3bf-bh and fig4 #cb2 ,galbreath1 #aidh3caf-cag and fig4 #a2 and ,black1 #aifa3ac-ad and fig4 #eh72 upper incisors unknown2 cheek teeth hyposodont1 persistently rooted1 and having crowns of medium height compared with ,recent geomyids2 enamel investment complete and uninterrupted in all molariform teeth in all stages of wear2 ,p#d unknown1 but probably formed like p#d2 p#d persistently biprismatic1 two crowns joined at mid-points by relatively narrow isthmus separating lateral re-entrant folds2 anterior lophid of p#d having distinct anteroexternal inflection2 molars also biprismatic throughout life2 two lophids of lower molars first uniting at mid-points as in p#d1 and1 with additional wear1 m#a and m#b secondarily uniting at edge of protomeres and forming isolated enamel fossette between point of connection 7detailed description of stages of wear discussed in account of phylogeny of subfamily72 m#c permanently joined at mid-point only1 without lateral union at edge of protomeres2 upper molars1 judging by ,m#a 7,m#b and ,m#c unknown71 having same pattern as lower molars1 but first union of lophs decidedly on lingual side of center1 consequently1 lingual re-entrant fold small2 ,m#a probably developing ,u-pattern in advanced stages of wear by union of protomeres1 with minute lingual fossette developing in transition as lophs secondarily become united at lingual edge of columns2 mandible stout and geomyidlike2 masseteric ridge weakly developed2 basitemporal fossa absent4 ,evidently1 ,dikkomys matthewi is more primitive than ,dikkomys woodi4 ,the modified ,h-pattern in m#a and m#b1 with the metalophid and hypolophid joined at both their mid-points and also at their protomeres 7by union of the protostylid and hypostylid in the lower dentition71 is persistent throughout life4 ,therefore1 the enclosed enamel fossette is not eradicated with wear4 ,in m#a and m#b of ,dikkomys woodi1 the fossette is shallower1 and1 at least in advanced stages of wear1 it would disappear1 therefore1 forming a ,u-pattern on the occlusal surface1 as in ,m#a and ,m#b1 but lateral inflection horizontally shallow rather than deep as in entoptychines4 ,specimen 7,no4 ,p #bfbhd ,,fmnh7 reported as ,dikkomys matthewi by ,galbreath 7#aidh3caf7 is referable to the recently described species ,dikkomys woodi ,black1 #aifa4 ,specimens examined4--,one1 no4 ,p #bfbhd1 ,field ,mus4 ,nat4 ,hist41 from upper ,rosebud1 ,shannon ,co41 ,south ,dakota4 ,referred species4--two3 ,dikkomys matthewi ,wood1 #aicf4 ,amer4 ,mus4 ,novit41 #hff3bf1 ,july4 ,type from early ,arikareean ,lower ,harrison deposits 7early ,miocene7 near ,agate1 ,sioux ,county1 ,nebraska4 ,dikkomys woodi ,black1 #aifa4 ,postilla1 ,yale ,peabody ,museum1 #dh3ac1 ,january #af4 ,type from ,deep ,river ,formation1 late ,hemingfordian 7middle ,miocene71 ,meagher ,county1 ,montana2 also known from ,upper ,rosebud deposits 7middle ,miocene7 near ,wounded ,knee1 ,shannon ,county1 ,south ,dakota4 ,genus ,pliosaccomys ,wilson #aicf4 ,pliosaccomys ,wilson1 ,carnegie ,inst4 ,washington ,publ41 #dgc3bj1 ,may #ba4 ,type4--,pliosaccomys dubius ,wilson1 #aicf1 from ,smiths ,valley local fauna in ,lyon ,county1 ,nevada4 ,chronologic range4--,early ,pliocene1 late ,clarendonian 7,wolf ,creek local fauna1 ,south ,dakota1 and ,nettle ,springs local fauna1 ,california7 to ,middle ,pliocene1 middle part of ,hemphillian 7,smiths ,valley local fauna1 ,nevada1 and ,mc,kay ,reservoir and ,otis ,basin local faunas1 ,oregon74 ,description4--,size small 7alveolar length of mandibular tooth-row measuring #f4j in holotype71 about as in ,thomomys monticola2 upper incisor relatively broad and flat1 having anterior face smooth1 without trace of grooving2 crowns of cheek teeth of medium height and rooted2 enamel investment continuous and uninterrupted in all stages of wear2 premolars permanently1 biprismatic2 ,p#d having anterior prism subtriangular and decidedly smaller that sub-crescentic posterior prism1 and joined near centers by narrow1 obliquely oriented isthmus2 p#d having anterior prism subovate1 posterior prism strongly compressed anteroposteriorly1 and joined at mid-points by relatively broad and straight isthmus2 first and second molars1 both above and below1 monoprismatic in final 78adult7 stage of wear1 derived ontogenetically from primitive bilophate pattern by coalescence of two columns into one2 ,m#a and ,m#b mirror images of m#a and m#b in pre-final stages of wear1 two columns first uniting at edge of protomeres forming ,u-pattern1 and primitive ,h-pattern never developing in either series 7for detailed description of stages of wear1 see account of phylogeny1 p4 #edf72 m#c 7,m#c unknown1 but probably with same form as in ,geomyini1 see p4 #eeb7 persistently biprismatic1 two columns joined by relatively broad isthmus at centers1 consequently1 forming ,h-pattern of primitive ancestors2 rostrum heavy and broad as in modern geomyids2 palate narrow and strongly ribbed2 mandible stout2 masseteric ridge and fossa well developed2 basitemporal fossa absent4 ,specimens examined4--,six1 nos4 #agif 7holotype7--#agii1 #ahjd and #ahjf 7,,cit7 now in the ,los ,angeles ,county ,museum1 all from ,smiths ,valley local fauna1 ,middle ,pliocene1 ,nevada4 ,referred species4--two3 99,pliosaccomys dubius ,wilson1 #aicf4 ,carnegie ,inst4 ,washington ,publ41 #gdc3bj1 ,may #ba4 ,known from early and middle ,pliocene faunas including ,wolf ,creek local fauna 7late ,clarendonian71 ,shannon ,county1 ,south ,dakota2 ,mc,kay ,reservoir local fauna and ,otis ,basin local fauna 7,hemphillian71 ,oregon2 type from ,smiths ,valley local fauna 7probably middle ,hemphillian71 ,lyon ,county1 ,nevada4 99,pliosaccomys wilsoni ,james1 #aifc4 ,univ4 ,california ,publ4 ,geol4 ,sci41 #de3aja1 ,june #bf4 ,type from ,nettle ,springs local fauna of late ,clarendonian 7early ,pliocene71 ,ventura ,county1 ,california4 ,tribe ,,thomomyini1 new tribe ,type4--,thomomys ,wied-,neuwied1 #ahci4 ,chronologic and geographic range4--,known from late ,pliocene 7early ,blancan7 to ,recent4 ,known primarily from western ,north ,america from southern ,canada south to ,central ,mxico in ,pliocene1 ,pleistocene and ,recent and in middle and late ,pleistocene of ,maryland and ,florida4 ,diagnosis4--,size small to medium 7basilar length exclusive of ,t4 bulbivorus1 measuring from approximately #bd to #de1 including both males and females72 upper incisors without grooving1 excepting fine1 indistinct sulcus rarely near inner margin 7grooving more common in ,t4 monticola than in other ,recent species72 crowns of cheek teeth high1 rooted and ever-growing2 all molars1 including ,m#c1 monoprismatic and anteroposteriorly compressed1 sometimes 7especially in subadults7 having slight inflection on labial side in upper teeth and lingual side in lower teeth2 molars bicolumnar in pre-final stages of wear 7seen in juvenal teeth only71 patterns of wear in both upper and lower molars resembling those of ,pliosaccomys1 except that crowns of m#c and ,m#c unite into single column in final stages of wear2 enamel pattern interrupted in all cheek teeth1 loss occurring only at sides of each column2 transverse enamel blade completely covering posterior face of both ,p#d and p#d2 all upper and lower molars with two transverse enamel blades1 one on anterior surface and one on posterior surface1 of each tooth1 including ,m#c2 small third plate sometimes persistent on broad side of tooth1 labial side in upper molars and lingual side in lower molars 7,t4 bulbivorus72 skull generalized1 neither unusually narrow and deep or broad and flat2 usually without marked cresting or rugosity2 masseteric ridge well developed and massive2 basitemporal fossa absent1 sometimes shallow depression forming in ,t4 townsendii2 pelage soft1 never harsh or hispid1 covering body with thick coat of hair2 forefoot exceptionally small for fossorial mammal1 claws not especially long2 body form remarkably fossorial4 ,the tribe ,thomomyini is monotypic1 including only the genus ,thomomys4 ,genus ,thomomys ,wied-,neuwied #ahci4 ,thomomys ,wied-,neuwied1 ,nova ,acta ,phys4 ,med4 ,acad4 ,caesar4 ,leop4-,carol41 #ai7a73cgg4 #ahcf4 ,oryctomys ,eydoux and ,gervais 7in part71 ,mag4 de ,zool41 #f3bj1 pl4 #ba4 ,type3 ,oryctomys 7,saccophorus7 bottae1 from coast of ,california1 probably near ,monterey4 #aijc4 ,megascapheus ,elliot1 ,field ,columb4 ,mus41 ,publ4 #gf1 ,zool4 ,ser41 #c7aa73aij1 ,july #be4 ,type3 ,diplostoma bulbivorum ,richardson1 from ,columbia ,river1 probably near ,portland1 ,ore4 #aicc4 ,pleisothomomys ,gidley and ,gazin1 ,jour4 ,mamm4 #ad3ced4 ,type3 ,pleisothomomys potomacensis ,gidley and ,gazin1 from ,pleistocene1 ,cumberland ,cave local fauna1 ,allegany ,county1 ,maryland4 ,chronologic range4--,known from late ,pliocene to ,recent4 ,description4--,same as that given for the tribe ,thomomyini above4 ,discussion4--,features characterizing ,thomomys and the tribe ,thomomyini are more advanced than those characterizing the tribe ,dikkomyini4 ,also1 the ,thomomyini retain more of the primitive features of the ,geomyinae than do the more specialized tribe ,geomyini4 ,specializations are few1 but include the third molar being a single column both above and below1 enamel plates1 and a masseteric ridge4 ,key to the ,subgenera of ,thomomys ,a ,molars sub-crescent or ovate in cross-section1 not becoming abruptly narrower at one end of tooth4 ,subgenus ,pleisothomomys p4 #eai ,a ,molars pear-shaped1 not sub-crescent or ovate1 in cross-section1 crown becoming abruptly narrow at one end of tooth4 ,subgenus ,thomomys p4 #ebj ,subgenus ,pleisothomomys ,gidley and ,gazin #aicc4 ,pleisothomomys ,gidley and ,gazin1 ,jour4 ,mamm41 #ad3ced1 ,november #ac4 ,type4--,pleisothomomys potomacensis ,gidley and ,gazin1 #aicc4 ,chronologic range4--,late ,pliocene 7,hagerman local fauna1 ,idaho7 to late ,pleistocene4 ,the latest records are from the fauna of ,saber-tooth ,cave1 ,florida1 a late ,pleistocene assemblage that probably was deposited in the ,sangamon4 ,the middle and late ,pleistocene records are from the eastern ,united ,states1 suggesting that the subgenus ,pleisothomomys was restricted to that region while the subgenus ,thomomys occupied the western ,united ,states and parts of ,canada and ,mxico as it does today4 ,description and ,comparison4--,separated from subgenus ,thomomys only on basis of sub-crescentic shaped molars 7only jaw fragments and isolated teeth known71 seemingly a primitive feature of the genus4 ,this dental structure continued into the late ,pleistocene2 none of the ,recent species expresses this feature of the molars1 although the molars of ,thomomys vetus of the late ,pleistocene 7,wisconsin deposits71 referred to the subgenus ,thomomys on the basis of its alleged relationship to ,thomomys townsendii 7see ,davis1 #aicg3aef-aeh71 are less distinctly pear-shaped1 and are more sub-crescentic1 than in any other known species of the subgenus ,thomomys4 ,pleisothomomys ,gidley and ,gazin 7loc4 cit47 was proposed as a genus but is here considered as of no more than subgeneric worth1 and is recognized because of the apparent constancy of the sub-crescentic molars in the earlier members of the genus and in those populations of ,thomomys occurring in ,pleistocene times in the eastern ,united ,states4 ,referred species4--,three 7all extinct73 99,thomomys gidleyi ,wilson1 #aicc4 ,carnegie ,inst4 ,washington ,publ4 #ddj3abb1 ,december4 ,type from ,hagerman beds1 late ,pliocene1 ,idaho4 99,thomomys potomacensis ,gidley and ,gazin1 #aicc4 ,jour4 ,mamm41 #ad3ced1 ,november #ac4 ,type from ,cumberland ,cave1 middle and late ,pleistocene1 ,maryland4 99,thomomys orientalis ,simpson1 #aibh4 ,amer4 ,mus4 ,novit41 #cbh3f1 ,october #bf4 ,type from ,saber-tooth ,cave1 late ,pleistocene1 ,florida4 ,subgenus ,thomomys ,wied-,neuwied #ahci4 ,thomomys ,wied-,neuwied1 ,nova ,acta ,phys4-,med4 ,acad4 ,caesar4 ,leop4 ,carol41 #ai7a73cgg4 #aijc4 ,megascapheus ,elliot1 ,field ,columb4 ,mus41 ,publ4 #gf1 ,zool4 ,ser41 #c 7#aa73aij1 ,july #be4 ,type3 ,diplostoma bulbivorum ,richardson1 from ,columbia ,river1 probably near ,portland1 ,oregon4 ,type4--,thomomys rufescens ,wied-,neuwied1 #ahci4 ,chronologic range4--,early ,pleistocene 7,broadwater-,lisco local fauna1 ,nebraska7 to ,recent4 ,numerous records1 mostly isolated teeth1 from nearly all stratigraphic levels of the ,pleistocene 7for details1 see account of fossil record74 ,description4--,molars pear-shaped in cross-section1 becoming abruptly narrow at one end of the tooth4 ,the teeth of the late ,pleistocene species ,thomomys vetus are less distinctly pear-shaped than other referred species 7see remarks in the description of the subgenus ,pleisothomomys74 ,essentially on the basis of its significantly larger size and details of the skull1 ,elliott 7#aijc3aij7 proposed subgeneric recognition of ,thomomys bulbivorus and described the subgenus ,megascapheus to include it4 ,also the molars of ,thomomys bulbivorus usually have a small enamel plate1 both above and below1 bordering the persistent inflection on the protomere end of the tooth2 each lateral plate is isolated from the transverse plates on the anterior and posterior walls of the tooth4 ,in my opinion these features do not warrant subgeneric recognition2 however1 these characters do distinctly separate ,thomomys bulbivorus from other groups of species1 and the character of the molars suggests retention of a primitive trait4 ,therefore1 ,i propose that the unique structure of this species be recognized by setting it apart in the bulbivorus species-group4 ,referred species4--,ten species1 three extinct1 placed in three species-groups 7the numerous subspecies of this genus are listed in ,miller and ,kellogg1 #aiee3bgf-ccb1 and ,hall and ,kelson1 #aiei3dab-ddg74 bulbivorus species-group ,thomomys bulbivorus 7,richardson1 #ahbi74 ,fauna ,boreali-,americana1 #a3bjf4 ,type from ,columbia ,river1 probably near ,portland1 ,oregon4 umbrinus species-group 99,thomomys scudderi ,hay1 #aiba4 ,proc4 ,u4 ,s4 ,nat4 ,mus41 #di3fad4 ,type from ,fossil ,lake beds1 late ,pleistocene1 ,oregon4 ,thomomys umbrinus 7,richardson1 #ahbi74 ,fauna ,boreali-,americana1 #a3bjb4 ,type from southern ,mxico1 probably near ,boca de ,monte1 ,veracruz4 ,thomomys bottae 7,eydoux and ,gervais1 #ahcf74 ,mag4 de ,zool41 ,paris1 #f3bc4 ,type from coast of ,california1 probably near ,monterey4 99,thomomys vetus ,davis1 #aicg4 ,jour4 ,mamm41 #ah3aef1 ,may #ab4 ,type from ,fossil ,lake beds1 late ,pleistocene1 ,oregon4 ,thomomys townsendii 7,bachman1 #ahci74 ,jour4 ,acad4 ,nat4 ,sci4 ,philadelphia1 #h3aje4 ,type probably from near ,nampa1 ,canyon ,co41 ,idaho 7erroneously given as ,columbia ,river74 talpoides species-group 99,thomomys microdon ,sinclair1 #aije4 ,bull4 ,dept4 ,geol4 ,univ4 ,california1 #d3ade-afa4 ,type from ,potter ,creek ,cave1 late ,pleistocene1 ,california4 ,thomomys monticola ,j4 ,a4 ,allen1 #ahic4 ,bull4 ,amer4 ,mus4 ,nat4 ,hist41 #e3dh1 ,april #bh4 ,type from ,mt4 ,tallac1 #gejj ft41 ,el ,dorado ,co41 ,california4 ,thomomys talpoides 7,richardson1 #ahbh74 ,zool4 ,jour41 #c3eah4 ,type locality fixed at near ,fort ,carlton 7,carlton ,house71 ,saskatchewan ,river1 ,saskatchewan1 ,canada4 ,thomomys mazama ,merriam1 #ahig4 ,proc4 ,biol4 ,soc4 ,washington1 #aa3bad1 ,july #ae4 ,type from ,anna ,creek1 #fjjj ft41 near ,crater ,lake1 ,mt4 ,mazama1 ,klamath ,co41 ,washington4 ,tribe ,,geomyini1 new tribe ,genotype4--,geomys ,rafinesque1 #ahag4 ,chronologic and geographic range4--,known from late middle ,pliocene deposits to ,recent4 ,the range of living members extends from extreme southern ,manitoba and the southeastern ,united ,states south to southern ,panam1 and probably northern ,colombia1 ,south ,america4 ,diagnosis4--,size small to large 7condylobasal length of skull #cc4j to #gc4j in adults1 including both sexes72 sexual dimorphism marked1 sometimes strongly1 females being smaller than males1 especially in cranial dimensions2 upper incisors invariably grooved1 number and position of grooves varying according to genus2 cheek teeth high-crowned and ever-growing1 except in one primitive genus 7,pliogeomys72 all three lower molars and ,m#a and ,m#b monoprismatic1 and elliptical in cross-section in final stages of wear 7teeth of young1 subadult1 and adult animals72 primitive biprismatic patterns 7as known from ,recent specimens7 occurring only in pre-final stages of wear 7teeth of juveniles only72 biprismatic patterns of lower molars as in ,dikkomys1 and upper molars as in ,pliosaccomys 7for detailed description of these patterns1 see account beyond of the phylogeny of the ,geomyinae72 m#c becoming monoprismatic1 anteroposteriorly compressed and elliptical in cross-section like m#a and m#b1 but ,m#c remaining1 with rare exceptions 7see accounts of ,geomys and ,pappogeomys beyond71 at least partially biprismatic throughout life1 having one or both lateral inflections usually persisting 7with exceptions7 and developing various occlusal shapes 7subtriangular1 elongate1 obcordate1 suborbiculate1 or quadriform7 but never elliptical4 ,enamel of cheek teeth reduced to interrupted plates1 with exception of p#d in ,pliogeomys2 plate on posterior wall of ,p#d variable1 occurring completely across posterior surface in primitive members1 but progressively reduced to lingual side only or completely lost in modern genera 7see generic accounts beyond for detailed description72 both anterior and posterior plates usually retained in ,m#a and ,m#b1 posterior plate sometimes reduced to lingual side or completely lost 7as in ,pappogeomys7 but anterior plate always completely retained2 ,m#c usually having three plates1 one anterior and two lateral2 posterior plate wanting 7sometimes lingual plate moved to posterior position72 plates retained completely across posterior walls of all lower cheek teeth with no reduction1 but anterior plates of m#a-c always lacking1 except in primitive genus ,pliogeomys 7only ,geomyini having both anterior and posterior enamel plates on lower molars74 ,skull primitively generalized1 but becoming specialized towards either dolichocephaly 7,orthogeomys7 or platycephaly 7,pappogeomys7 in two modern genera2 skull highly specialized for fossorial life2 mandible stout and deep1 angular process being high and diverging laterally at right angles to ramus2 masseteric ridge and fossa weakly developed in primitive members1 becoming well developed and massive in modern genera2 basitemporal fossa absent in primitive forms 7,pliogeomys and early members of ,zygogeomys72 pelage usually soft1 but harsh and hispid in some genera2 forefeet broad and massive1 claws long and stout for digging2 body form remarkably fossorial4 ,the tribe ,geomyini includes the most highly specialized members of the subfamily ,geomyinae4 ,key to the ,genera of the ,tribe ,geomyini ,a ,cheek teeth rooted2 p#d with uninterrupted enamel loop2 enamel plates on both anterior and posterior walls of m#a and m#b2 masseteric ridge weakly developed1 low1 not massive4 ,genus ,pliogeomys p4 #ebb ,a ,cheek teeth rootless1 ever-growing2 p#d with enamel investment interrupted at ends of columns1 consequently1 forming four isloted plates2 enamel plate retained only on posterior wall of m#a and m#b1 anterior wall without trace of enamel 7except rarely in pre-final stage of wear in ,geomys tobinensis of middle ,pleistocene72 masseteric crest strongly developed and massive4 ,b ,enamel plate on posterior wall of ,p#d1 but usually restricted to lingual end of tooth 7usually absent in subgenus ,orthogeomys of genus ,orthogeomys72 ,m#c conspicuously bicolumnar1 longer than wide owing to elongation of posterior loph4 ,c ,upper incisor bisulcate2 skull generalized2 rostrum relatively narrow2 length of labial enamel plate of ,m#c decidedly less than length of lingual plate2 pelage soft and thick4 ,genus ,zygogeomys p4 #ebc ,c ,upper incisor unisulcate2 skull strongly dolichocephalic2 rostrum remarkably broad and massive2 length of lingual plate of ,m#c approximately equal to1 or greater than1 length of labial plate2 pelage harsh1 often hispid and scant4 ,genus ,orthogeomys p4 #ebh ,b ,posterior wall of ,p#d without trace of enamel2 ,m#c not strongly bicolumnar1 having shallow re-entrant fold on labial side1 and crown no longer than wide owing to shortness of posterior loph4 ,d ,upper incisor bisulcate2 skull generalized2 both anterior and posterior walls of ,m#a and ,m#b having complete enamel plates4 ,genus ,geomys p4 #ebe ,d ,upper incisor unisulcate2 skull generalized or tending towards platycephaly2 enamel plate on posterior wall of ,m#a usually reduced to lingual side or absent 7complete only in one species1 ,pappogeomys bulleri72 enamel plate on posterior wall of ,m#b also absent in advanced species 7subgenus ,cratogeomys74 ,genus ,pappogeomys p4 #ecb ,genus ,pliogeomys ,hibbard #aied4 ,pliogeomys ,hibbard1 ,michigan ,acad4 ,sci41 ,arts and ,letters1 #ci3cec4 ,genotype4--,pliogeomys buisi ,hibbard1 #aied1 from ,buis ,ranch local fauna 7middle ,pliocene71 ,beaver ,county1 ,oklahoma4 ,chronologic range4--,latest ,middle ,pliocene1 known only from the highest part of the ,hemphillian mammalian fauna 7,buis ,ranch local fauna1 ,oklahoma74 ,professor ,hibbard informs me 7personal communication7 that he found the type1 a right ramus1 lying on the surface near the base of the fossil beds4 ,the isolated teeth of small geomyids from the ,saw ,rock ,canyon local fauna 7see ,hibbard1 #aiec3cib7 may also be referable to this genus4 ,the ,saw ,rock ,canyon local fauna may also be middle ,pliocene in age but is considered to be from the later part of the late ,pliocene1 and1 therefore1 somewhat younger than the ,buis ,ranch local fauna 7,hibbard1 op4 cit43#cdb74 ,description and discussion4--,the size of members of this small genus of the ,geomyinae is about the same as in smaller adults of ,geomys bursarius4 ,according to ,hibbard 7op4 cit43#cec71 the holotype is smaller than specimens from the ,rexroad local fauna referred to ,geomys quinni and larger than specimens referred to ,zygogeomys cf4 minor4 ,the cheek teeth are rooted1 and the crowns are as high as those of living geomyids4 ,the upper incisor is bisulcate1 and the inner groove is fine and indistinct in places4 ,of the molariform dentition only the lower premolar and first two lower molars are known4 ,the enamel investment of p#d is complete1 and would not be subject to interruption at any stage of wear2 the two prisms are joined at their mid-points1 and the isthmus of dentine is relatively broad 7as in ,pliosaccomys7 when compared with modern pocket gophers of this tribe4 ,also1 the re-entrant folds1 rather than having parallel sides1 diverge broadly to the sides4 ,the divergence is especially noticeable in the labial fold4 ,the lower deciduous premolar would have formed essentially the same enamel pattern with wear as observed in ,nerterogeomys ,zygogeomys cf4 minor 7see ,hibbard1 #aied3;fig4 #e1 ,a and ,b7 and ,pliosaccomys dubius 7see ,wilson1 #aicf2 pl4 #a1 fig4 #a74 ,each molar is a single column in the final stages of wear2 pre-final stages are unknown4 ,anterior and posterior enamel plates are present on m#a and m#b 7m#c has not been recovered74 ,the dentine tracts of m#a are exposed over a relatively wide surface2 therefore1 the enamel plates are distinctly separated4 ,the tracts of dentine of m#b are much narrower than in m#a and the enamel plates are barely separated at the anterolateral margin of the tooth4 ,possibly the enamel band of m#b was continuous in an earlier stage of wear4 ,the mandible is stout and its general construction not unlike that in modern geomyines4 ,the capsule at the base of the angular process that receives the terminal end of the lower incisor is well developed4 ,the base of the angular processes is preserved1 and suggests that the process was short and decidedly smaller than in living examples of the tribe4 ,the masseteric ridge is distinct but weakly developed1 and not at all massive as in living pocket gophers4 ,the mental foramen is immediately anterior1 and slightly ventral1 to the anterior extension of the crest4 ,the basitemporal fossa is absent as such1 but its position is marked by a slight depression4 ,specimens examined4--,two rami2 nos4 #biadg 7holotype7 and #ccddf2 several isolated teeth #cjaid and #cjaie1 including an upper incisor and a dp#d 7deciduous lower premolar71 all from ,univ4 ,michigan ,mus4 ,paleo4 ,referred species4--,one4 99,pliogeomys buisi ,hibbard1 #aied4 ,papers ,michigan ,acad4 ,sci41 ,arts1 and ,letters1 #ci3cec4 ,type from ,buis local fauna1 latest middle ,pliocene1 ,beaver ,county1 ,oklahoma4 ,genus ,zygogeomys ,merriam #ahie4 ,zygogeomys ,merriam1 ,n4 ,amer4 ,fauna1 #h3aie1 ,january #ca4 #aidb4 ,nerterogeomys ,gazin1 ,proc4 ,u4 ,s4 ,nat4 ,mus41 #ib3ejg 7type1 ,geomys persimilis ,hay1 #aibg74 ,type4--,zygogeomys trichopus ,merriam1 #ahie1 from ,nahuatzen1 ,michoacn4 ,chronologic range4--,late ,pliocene 7,benson and ,curtis ,ranch local faunas1 ,arizona1 and 8,rexroad ,formation1 ,kansas7 to ,recent4 ,description and discussion4--,the size is small to medium for the subfamily ,geomyinae4 ,this genus is distinguished principally by the retention of primitive features4 ,in the living species1 the skull is generalized1 rather than specialized toward either extreme dolichocephaly or platycephaly4 ,the angular process is short1 barely exceeding the lateral extensions of the mastoid process of the squamosal4 ,the rostrum is remarkably narrow in relation to its length4 ,the jugal is reduced and displaced ventrally1 causing the maxillary arm of the zygomata to articulate with the squamosal arm of the zygomata along the dorsal border of the zygomatic arch 7a feature observed also in ,orthogeomys cherriei costaricensis74 ,the upper incisor1 recovered in material from the late ,pliocene and middle ,pleistocene1 is bisulcate as in the genus ,geomys and the primitive genus ,pliogeomys4 ,the enamel plate across the posterior wall of ,p#d is either complete 7late ,pliocene to late ,pleistocene7 or restricted to the lingual half of the tooth 7always restricted in living species74 ,the ,pliocene specimens of the ,rexroad local fauna referred to ,nerterogeomys cf4 minor by ,hibbard 7#aiej3ach-aci7 are exceptional4 ,in these specimens the length and position of the posterior enamel plate is variable2 however1 all but one specimen had persistant enamel4 ,evidently1 in approximately #dc per cent of the specimens1 a complete enamel blade was present 7see ,paulson1 #aifa3aci71 and in the others 7except the one without any enamel7 the plate was restricted to a small area of the ventral surface1 usually on the lingual side of the loph4 ,hibbard suggested that the decrease in size of the plate1 and its restriction to the lingual side1 may be a function of age4 ,hence1 most adults would be characterized by the reduced posterior plate on the upper premolar4 ,although age may be the important factor1 intragroup variation cannot be ruled out4 ,it is of interest to note that in all specimens from the ,benson 7type series of ,p4 minor7 and ,curtis ,ranch local faunas1 the former of late ,pliocene age and the latter of middle ,pleistocene age1 the enamel plates are complete on the posterior face of the upper premolar4 ,as mentioned before1 the specimens from ,kansas may actually represent the transitional stages of the early evolution of ,geomys in which the posterior plate of ,p#d is entirely lost4 ,the enamel pattern of p#d is like that in other members of the tribe 7excepting the genus ,pliogeomys74 ,the re-entrant angles of ,p#d and p#d are widely open 7obtuse7 in the examples recovered from late ,pliocene and middle ,pleistocene deposits1 representing retention of a trait that is primitive in the ,geomyini 7see account of phylogeny74 ,m#a and ,m#b are elliptical in cross-section and each has an enamel plate on both the anterior and posterior surface4 ,in the living species 7,z4 trichopus71 the posterior enamel plate fails to reach the labial margin of the tooth and is restricted to the lingual two-thirds of the posterior surface2 however1 the enamel plates are complete in the late ,pliocene species 7,z4 minor7 and the middle ,pleistocene species 7,z4 persimilis71 being only slightly separated from the anterior plate by narrow tracts of dentine on the ends of the tooth4 ,m#c is partly biprismatic in the living species1 the two incompletely divided lophs being separated by a distinct outer sulcus4 ,the posterior loph is elongated and forms a conspicuous heel paralleling the evolution of this trait in the genus ,orthogeomys2 therefore1 the crown is longer than wide4 ,the posterior part of the tooth is protected by two lateral enamel plates2 of the two1 the lingual plate is especially long and extends to the end of the heel4 ,m#c has not been recovered in the ,pliocene species1 but in the middle ,pleistocene species 7,z4 persimilis7 ,m#c is subtriangular1 no longer than wide1 and the lateral inflections are weakly developed4 ,the trend towards elongation of ,m#c evidently occurred in late ,pleistocene evolution of the genus4 ,all three of the inferior molars are elliptical1 and only the posterior enamel plate is present 7as in all other genera of the tribe except ,pliogeomys74 ,the masseteric ridge of the mandible is well developed4 ,in the late ,pliocene species ,z4 persimilis and ,z4 minor the mental foramen is directly beneath the anterior extension of the masseteric ridge1 but in the living species1 ,z4 trichopus1 the foramen lies well anterior to the ridge4 ,the basitemporal fossa in the living species is well developed and deep2 in the ,pliocene species it is usually distinct but shallow 7late ,pliocene specimens of ,z4 minor74 ,referred species4--,three 7two extinct and one living2 the last has two subspecies73 99,zygogeomys minor 7,gidley71 #aibb4 ,u4 ,s4 ,geol4 ,surv4 ,prof4 ,paper1 #aca3abc1 ,december #bf4 ,type from ,benson local fauna 7late ,pliocene71 ,cochise ,county1 ,arizona2 also known from the ,rexroad local fauna1 ,meade ,county1 ,kansas4 99,zygogeomys persimilis ,hay1 #aibg4 ,carnegie ,inst4 ,washington ,publ41 #acf4 ,originally described by ,gidley1 #aibb 7,u4 ,s4 ,geol4 ,surv4 ,prof4 ,papers1 #aca3abc1 ,december #bf7 as ,geomys parvidens which was preoccupied by ,g4 parvidens ,brown1 #aijh4 ,type from ,curtis ,ranch local fauna 7middle ,pleistocene71 ,cochise ,county1 ,arizona4 ,zygogeomys trichopus trichopus ,merriam1 #ahie4 ,n4 ,amer4 ,fauna1 #h3aif1 ,january #ca4 ,type from ,nahuatzen1 ,michoacn4 ,zygogeomys trichopus tarascensis ,goldman1 #aich4 ,proc4 ,biol4 ,soc4 ,washington1 #ea3baa1 ,december #bc4 ,type from #f mi4 ,,se ,ptzcuaro1 #h1jjj ft41 ,michoacn4 ,genus ,geomys ,rafinesque #ahag4 ,geomys ,rafinesque1 ,amer4 ,monthly ,mag41 #b7a73de1 ,november4 #ahag4 ,diplostoma ,rafinesque1 ,amer4 ,monthly ,mag41 #b7a73dd-de1 ,november4 ,included species3 ,diplostoma fusca ,rafinesque ,mus bursarius ,shaw and ,diplostoma alba ,rafinesque ,mus bursarius ,shaw from the ,missouri ,river region4 #ahbj4 ,saccophorus ,kuhl1 ,beitr4 ,zool4 und ,vergl4 ,anat41 pp4 #fe1 #ff4 ,type3 ,mus bursarius ,shaw1 from upper ,mississippi ,valley4 #ahbc4 ,pseudostoma ,say1 ,long's ,expd4 ,rocky ,mts41 ,i1 pp4 #djf4 ,type3 ,pseudostoma bursaria ,mus bursarius ,shaw1 from upper ,mississippi ,valley4 #ahbe4 ,ascomys ,lichtenstein1 ,abh4 ,k4 ,akad4 ,wiss4 ,berlin 7#ahbb71 p4 #bj41 fig4 #b4 ,type3 ,ascomys canadensis ,lichtenstein ,mus bursarius ,say1 probably from upper ,mississippi ,valley4 #aidd4 ,parageomys ,hibbard1 ,bull4 ,geol4 ,soc4 ,amer41 #ee3gce1 ,june4 ,type3 ,parageomys tobinensis ,hibbard1 from ,pleistocene1 ,cudahy 7,tobin7 local fauna1 ,russell ,co41 ,kansas4 ,type4--,geomys pinetis ,rafinesque1 #ahag1 restricted to ,screven ,county1 ,georgia1 in region of the pines4 ,chronologic range4--,late ,pliocene faunas of ,blancan age 7,rexroad1 ,kansas1 and ,sand ,draw1 ,nebraska1 local faunas7 to ,recent4 ,reported from numerous ,pleistocene deposits of all stratigraphic levels1 especially from the ,great ,plains1 where common today4 ,description and discussion4--,pocket gophers of this genus are medium-sized geomyids2 none is so small as the average-sized ,thomomys4 ,the skull is generalized and lacks the dolichocephalic and platycephalic specializations seen in the genera ,orthogeomys and ,pappogeomys1 respectively4 ,geomys closely resembles ,zygogeomys1 but retains fewer of the primitive characters of the ancestral stock4 ,at the same time1 ,geomys has several specializations4 ,even so1 a considerable amount of parallelism is evident in the phyletic trends of the two genera4 ,the upper incisor of ,geomys is bisulcate as in ,pliogeomys and ,zygogeomys2 the deeper grove is medial and the shallower grove lies near the inner border of the tooth4 ,the premolar1 above and below1 is bicolumnar2 and two columns are joined at their mid-points 7deep re-entrant angles separate the columns at the sides74 ,a permanent enamel plate protects the anterior face of the anterior loph1 and enamel bands outline each of the re-entrant folds4 ,in p#d a complete enamel plate covers the posterior surface of the posterior loph4 ,all of the enamel bands are interrupted by tracts of dentine1 except in the initial stages of wear of the occlusal surface of the newly erupted tooth4 ,for a short time in living ,geomys1 the enamel bands are continuous as observed in juveniles of ,geomys bursarius major 7,,ku #efbh1 #heca1 and #daedj74 ,but1 the enamel cap is thin and the dentine tracts1 which are high on the sides of the tooth1 are soon revealed by a minimum of wear on the crown4 ,therefore1 the adult1 or final1 pattern characterized by interrupted enamel plates emerges early in life and remains throughout the life of the individual4 ,evidence from fossil ,geomys1 especially from specimens from early and late ,pleistocene deposits1 suggests that the final adult pattern appears later1 ontogenetically1 than in ,recent specimens4 ,some of the fossil premolars in initial stages of wear have continuous and uninterrupted bands of enamel4 ,geomys quinni of the late ,pliocene and early ,pleistocene has the interrupted pattern seen in late ,pleistocene and ,recent ,geomys4 ,also1 in late ,pliocene and early ,pleistocene species1 the re-entrant folds diverge laterally and form open angles4 ,in later taxa 7middle ,pleistocene to ,recent7 the folds are compressed and parallel-sided1 and the open folds are found only in the early stages of wear4 ,the posterior enamel plate of ,p#d disappears in the final stages of wear as the interrupted enamel pattern is formed4 ,in the late ,pleistocene and ,recent ,geomys1 the loss of the posterior plate occurs early in life1 usually in the first phases of wear on the occlusal surface of the newly erupted tooth1 but in fossils of ,geomys of corresponding ontogenetic age from the early and middle ,pleistocene1 the posterior plate is retained in some individuals until a later phase of wear1 thereby delaying the appearance of the final pattern4 ,indeed1 in five or fewer per cent of the individuals 7see ,paulson1 #aifa3ach-aci2 and ,white and ,downs1 #aifa3ah7 a vestige of enamel is retained throughout life or at least until late in adulthood4 ,in ,geomys tobinensis1 for example1 a thin1 but transversely complete1 plate of enamel occurs all the way down to the base of the loph 7,paulson1 loc4 cit47 and would persist throughout life4 ,in ,geomys garbanii1 a vestige on the lingual side of the posterior surface of a fully adult specimen was noted by ,white and ,downs 7loc4 cit474 ,vestiges of the posterior plate occur less frequently in living geomyids4 ,paulson 7loc4 cit47 found a posterior plate in one of #ge specimens of ,geomys bursarius dutcheri4 ,a young 7suture present between exoccipitals and supraoccipital7 female of ,geomys pinetis austrinus 7,,ku #bcceh7 has a vestige of the posterior plate on the lingual side of the tooth as ,white and ,downs 7loc4 cit47 observed in a specimen of ,geomys garbanii4 ,the enamel1 ,i suspect1 tends to be thicker on the lingual than on the labial side of the loph and extends farther down the lingual surface in some individuals2 therefore1 wear on the occlusal surface erodes it down to the dentine more rapidly on the labial than on the lingual side4 ,the tendency of enamel to be retained is a primitive feature4 ,a lower molar of ,geomys is a single elliptical column1 and enamel is restricted to the posterior surface as in ,zygogeomys1 ,orthogeomys1 and ,pappogeomys4 ,paulson 7loc4 cit47 found a thin enamel plate on the anterior surfaces of the lower molars in about five per cent of the individuals of ,geomys tobinensis from the ,cudahy local fauna 7middle ,pleistocene1 deposits of the late ,kansan glaciation74 ,an anterior plate is unknown in other members of the tribe ,geomyini1 except in the primitive genus ,pliogeomys of the middle ,pliocene4 ,occurrence of the plate in ,geomys tobinensis is an atavistic trait4 ,primitive dental patterns occur occasionally in geomyids1 as pointed out above1 but the frequency of occurrence in ,g4 tobinensis is higher than would be expected4 ,m#a and ,m#b1 like the lower molars1 are elliptical in cross-section4 ,complete enamel plates on the anterior and posterior surfaces are separated by tracts of dentine on the sides of each tooth4 ,m#c is usually suborbicular 7sometimes subtriangular7 in cross-section4 ,the tooth is not especially elongated posteriorly and usually has no definite heel2 therefore1 it is not significantly longer than wide4 ,living species of ,geomys rarely have a well defined outer re-entrant fold on ,m#c2 less than #aj per cent of the individuals 7and usually only one side in each individual in which it occurs7 have it1 although a shallow inconspicuous groove occurs more frequently4 ,the biprismatic molar characteristic of the ancestral morphotype is less often found in ,geomys than in any other living member of the tribe ,geomyini4 ,the outer re-entrant fold and biprismatic pattern are more often present in the extinct species ,geomys garbanii of the ,middle ,pleistocene than in other species4 ,less than #bd per cent of the third upper molars in ,geomys garbanii lack a tract of the re-entrant fold and more than #ch per cent have a well developed outer fold 7see ,white and ,downs1 #aifa3ac1 #ah74 ,the bicolumnar pattern1 although incomplete1 would be clearly evident in those teeth having a well marked re-entrant fold2 the pattern occurs less frequently in those teeth with no fold or only a slight one4 ,m#c of geomyids is not usually recovered and1 therefore1 the occlusal pattern of ,m#c is unknown in most extinct kinds of ,geomys4 ,in ,recent ,geomys the fold is more common in the eastern pinetis species-group than in the western bursarius species-group4 ,the masseteric ridge on the outer side of the mandible is well developed in all species of the genus4 ,the position of the mental foramen relative to the anterior part of the ridge varies with individuals and according to species4 ,the basitemporal fossa is always present1 but is shallower in the late ,pliocene and ,pleistocene species than in ,recent species4 ,the angular process is short4 ,referred species4--,the twelve species1 five of which are extinct1 are as follows3 quinni species-group 99,geomys quinni ,mc,grew1 #aidd4 ,geol4 ,ser41 ,field ,mus4 ,nat4 ,hist41 #i 7#edf73di1 ,january #bj4 ,type from ,sand ,draw local fauna 7late ,pliocene71 ,brown ,county1 ,nebraska2 also known from ,broadwater-,lisco local faunas 7early ,pleistocene71 ,morrill and ,garden counties1 ,nebraska1 ,deer ,park local fauna 7early ,pleistocene71 ,meade ,county1 ,kansas4 99,geomys paenebursarius ,strain1 #aiff4 ,bull4 ,texas ,memorial ,mus41 #aj3cf4 ,type from ,hudspeth local fauna 7early ,pleistocene71 ,hudspeth ,county1 ,texas4 99,geomys tobinensis ,hibbard1 #aidd4 ,bull4 ,geol4 ,soc4 ,amer41 #ee3gcf4 ,type from ,tobin local fauna 7middle ,pleistocene71 ,russell ,county1 ,kansas2 also known from ,cudahy local fauna 7middle ,pleistocene71 ,meade ,county1 ,kansas4 99,geomys garbanii ,white and ,downs1 #aifa4 ,contrib4 ,sci41 ,los ,angeles ,co4 ,mus41 #db3a-cd1 ,june #cj4 ,type from ,vallecito ,creek local fauna 7middle ,pleistocene71 ,san ,diego ,county1 ,california4 99,geomys bisulcatus ,marsh1 #ahga4 ,amer4 ,jour4 ,sci41 #c3aba4 ,type from ,loup ,river fossil beds1 near ,camp ,thomas1 ,nebraska 7probably late ,pleistocene74 bursarius species-group 99,geomys parvidens ,brown1 #aijh4 ,mem4 ,amer4 ,mus4 ,nat4 ,hist41 #i3aid4 7,an extinct subspecies of ,geomys bursarius according to ,white and ,downs1 #aifa3f74 ,type from ,conard ,fissure local fauna 7late ,pleistocene71 northern ,arkansas4 ,geomys bursarius 7,shaw1 #ahjj74 ,trans4 ,linn4 ,soc4 ,london1 #e3bbg4 ,type from somewhere in ,upper ,mississippi ,valley1 ,north ,america4 ,geomys arenarius ,merriam1 #ahie4 ,n4 ,amer4 ,fauna1 #h3aci1 ,january #ca4 ,type from ,el ,paso1 ,el ,paso ,county1 ,texas4 ,geomys personatus ,true1 #ahhi4 ,proc4 ,u4 ,s4 ,nat4 ,mus41 #aa3aei1 ,january #e4 ,type from ,padre ,island1 ,cameron ,county1 ,texas4 pinetis species-group ,geomys pinetis ,rafinesque1 #ahjf4 ,amer4 ,monthly ,mag41 #b 7#a73de1 ,november4 ,type locality restricted to ,screven ,county1 ,georgia4 ,geomys colonus ,bangs1 #ahih4 ,proc4 ,boston ,soc4 ,nat4 ,hist41 #bh3agh1 ,march4 ,type from ,arnot ,plantation1 about #d mi4 ,w ,st4 ,marys1 ,camden ,county1 ,georgia4 ,geomys cumberlandius ,bangs1 #ahih4 ,proc4 ,boston ,soc4 ,nat4 ,hist41 #bh3ahj1 ,march4 ,type from ,stafford ,place1 ,cumberland ,island1 ,camden ,county1 ,georgia4 ,geomys fontanelus ,sherman1 #aidj4 ,jour4 ,mamm41 #ba3cda1 ,august #ac4 ,type from #g mi4 ,,nw ,savannah1 ,chatham ,county1 ,georgia4 ,genus ,orthogeomys ,merriam #ahie4 ,orthogeomys ,merriam1 ,n4 ,amer4 ,fauna #h3agb1 ,january #ca4 #ahie4 ,heterogeomys ,merriam1 ,n4 ,amer4 ,fauna #h3agi1 ,january #ca 7type1 ,geomys hispidus ,le ,conte1 #ahfb74 #ahie4 ,macrogeomys ,merriam1 ,n4 ,amer4 ,fauna #h3ahe1 ,january #ca 7type1 ,geomys heterodus ,peters1 #ahfe74 ,type4--,geomys scalops ,thomas1 #ahid1 from ,tehuantepec1 ,oaxaca1 ,mxico4 ,chronologic range4--,late ,pleistocene ,wisconsin deposits 7,san ,josecito ,cave local fauna1 ,nuevo ,len1 ,mxico7 to ,recent4 ,description and discussion4--,species of this genus are of medium to large size4 ,the skull is strongly dolichocephalic in most species2 the posterior part of the skull is especially narrow4 ,the angular processes are remarkably short1 especially in relation to the length of the mandible4 ,the nasals and rostrum are relatively broad and heavy4 ,the pelage is coarse1 and often hispid4 ,in some species the hairs are so sparsely distributed that the body appears almost naked1 and none has so dense a covering of hair as do other genera4 ,the genus occurs entirely within the tropical life-zones1 and most of the external features seem to be associated with adaptation to tropical conditions4 ,the upper incisor is unisulcate2 the sulcus is usually near the inner border of the tooth1 but in some species 7subgenus ,orthogeomys7 it is more medial1 and in a few individuals with an extremely wide groove the outer lip of the sulcus may actually reach the middle of the tooth4 ,the groove is compressed or open4 ,the premolar is a double column united at the mid-point4 ,the two prisms are of approximately equal size1 and the lateral re-entrant folds are so compressed that their sides are parallel4 ,enamel plates cover the anterior surface and border the re-entrant angles in both upper and lower premolars4 ,as in other members of the tribe1 the lower premolar has a fourth enamel plate on the posterior surface of the posterior lophid4 ,in the upper premolar1 the enamel plate is reduced to a narrow blade on the lingual side of the loph as in the living species of the genus ,zygogeomys4 ,in the subgenus ,orthogeomys the posterior plate is usually absent1 and otherwise is narrow and near the lingual border of the tooth4 ,each lower molar1 in the final stage of wear1 consists of a single elliptical column having an enamel plate only on the posterior surface4 ,the first and second upper molars are single elliptical columns having one enamel plate on the anterior surface and another on the posterior surface4 ,the plates are separated by a tract of dentine on each side of the tooth4 ,the third upper molar is partly bilophodont1 and the two lophs are separated by a deep outer re-entrant fold4 ,in many of the species an inner re-entrant fold also is retained1 but in the adult tooth it is less distinct than the outer4 ,in all of the species the posterior loph is long and forms a conspicuous heel2 consequently the crown is significantly longer then wide4 ,moreover1 the posterior loph has an enamel plate on each side4 ,the labial plate always borders the outer re-entrant fold1 and in the subgenus ,orthogeomys is infrequently separated into two small plates4 ,the mandible is relatively long4 ,its masseteric ridge is well developed and massive4 ,the basitemporal fossa is usually deep and well defined2 it tends to be shallow in the subgenus ,orthogeomys1 and in young individuals is hardly more than a slight depression4 ,key to the ,subgenera of ,orthogeomys ,a ,frontal wide and greatly inflated2 no interorbital constriction2 enamel plate on posterior wall of ,p#d usually absent1 although sometimes having small plate1 restricted to lingual end of wall4 ,subgenus ,orthogeomys p4 #ebi ,a ,frontal narrow and not greatly inflated2 interorbital region decidedly constricted2 enamel plate on posterior wall of ,p#d always present but short and restricted to lingual end of wall4 ,b ,anterior margin of mesopterygoid fossa even with plane of posterior wall of ,m#c2 postorbital bar weakly developed2 anteroposterior occlusal length of ,m#c equal to1 or less than1 combined length of ,m#a and ,m#b4 ,subgenus ,heterogeomys p4 #ecj ,b ,anterior margin of mesopterygoid fossa decidedly behind plane of posterior wall of ,m#c2 postorbital bar strongly developed2 anteroposterior occlusal length of ,m#c more than combined length of ,m#a and ,m#b4 ,subgenus ,macrogeomys p4 #eca ,subgenus ,orthogeomys ,merriam #ahie4 ,orthogeomys ,merriam1 ,n4 ,amer4 ,fauna1 #h3agb1 ,january #ca4 ,type4--,geomys scalops ,thomas1 #ahid1 from ,tehuantepec1 ,oaxaca1 ,mxico4 ,chronologic range4--,known only from the ,recent4 ,description4--,skull elongated and narrow 7many skulls of nearly uniform breadth throughout71 being extreme in dolichocephalic specializations2 mandibles long and narrow1 rami not spreading laterally1 being more nearly parallel-sided than in other subgenera2 angular processes short2 breadth across zygomata not significantly exceeding breadth across mastoid processes 7in many skulls considerably less72 interorbital area remarkably broad1 lacking deep constriction2 frontals between orbits greatly inflated laterally1 postorbital prominence inconspicuous2 mesopterygoid fossa extending to level of posterior margin of ,m#c2 ,i having sulcus broader than in other subgenera1 mostly on inner half of anterior surface but sometimes overlapping mid-line2 enamel plate lacking from posterior wall of ,p#d1 rarely retaining narrow vestige near lingual border of posterior loph2 ,m#c having distinct heel1 bicolumnar pattern with inner re-entrant fold usually minute1 occlusal length less than in other subgenera1 length less than combined lengths of ,m#a-b2 hair generally coarse1 sometimes hispid1 sparse1 in lowland forms1 so sparse as to impart appearance of nakedness4 ,referred species and subspecies4--,fourteen taxa3 ,orthogeomys grandis alleni ,nelson and ,goldman1 #aicj4 ,jour4 ,mamm41 #aa3aef1 ,may #i4 ,type from near ,acapulco1 #bjjj ft41 ,guerrero4 ,orthogeomys grandis annexus ,nelson and ,goldman1 #aicc4 ,proc4 ,biol4 ,soc4 ,washington1 #df3aie1 ,october #bf4 ,type from ,tuxtla ,gutierrez1 #bfjj ft41 ,chiapas4 ,orthogeomys grandis carbo ,goodwin1 #aief4 ,amer4 ,mus4 ,novit41 #ageg3e1 ,march #h4 ,type from ,excurano1 #bejj ft41 ,cerro de ,san ,pedro1 #bj km4 ,w ,mixtequilla1 ,oaxaca4 ,orthogeomys grandis felipensis ,nelson and ,goldman1 #aicj4 ,jour4 ,mamm41 #aa3aeg1 ,may #i4 ,type from ,cerro ,san ,felipe1 #aj mi4 ,n ,oaxaca1 ,oaxaca4 ,orthogeomys grandis huixtlae ,villa1 #aidd4 ,anal4 ,inst4 ,biol4 ,univ4 ,nac4 ,mxico1 #ae3cai4 ,type from ,finca ,lubeca1 #ab km4 ,,ne ,huixtla1 #hej m41 ,chiapas4 ,orthogeomys grandis grandis 7,thomas1 #ahic74 ,ann4 ,mag4 ,nat4 ,hist41 ser4 #f1 #ab3bgj1 ,october4 ,type from ,dueas1 ,guatemala4 ,orthogeomys grandis latifrons ,merriam1 #ahie4 ,n4 ,amer4 ,fauna1 #h3agh1 ,january #ca4 ,type from ,guatemala1 exact locality unknown4 ,orthogeomys grandis nelsoni ,merriam1 #ahie4 ,n4 ,amer4 ,fauna1 #h3agf1 ,january #ca4 ,type from ,mt4 ,zempoaltepec1 #hjjj ft41 ,oaxaca4 ,orthogeomys grandis pluto ,lawrence1 #aicc4 ,proc4 ,new ,england ,zool4 ,club1 #ac3ff1 ,may #h4 ,type from ,cerro ,cantoral1 north of ,tegucigalpa1 ,honduras4 ,orthogeomys grandis scalops 7,thomas1 #ahid74 ,ann4 ,mag4 ,nat4 ,hist41 ser4 #f1 #ac3dcg1 ,may4 ,type from ,tehuantepec1 ,oaxaca4 ,orthogeomys grandis soconuscensis ,villa1 #aidi4 ,anal4 ,inst4 ,biol4 ,univ4 ,nac4 ,mxico1 #ai3bfg1 ,april #h4 ,type from ,finca ,experanza1 #gaj m41 #de km4 7by road7 ,,nw ,huixtla1 ,chiapas4 ,orthogeomys grandis guerrerensis ,nelson and ,goldman1 #aicj4 ,jour4 ,mamm41 #aa3aeh1 ,may #i4 ,type from ,el ,limn1 in valley of ,ro de las ,balsas approximately #bj mi4 ,,nw ,la ,unin1 ,guerrero4 ,orthogeomys cuniculus ,elliot1 #aije4 ,proc4 ,biol4 ,soc4 ,washington1 #ah3bcd1 ,december #i4 ,type from ,zanatepec1 ,oaxaca4 ,orthogeomys pygacanthus ,dickey1 #aibh4 ,proc4 ,biol4 ,soc4 ,washington1 #da3i1 ,february #a4 ,type from ,cacaguatique1 #cejj ft41 ,dept4 ,san ,miguel1 ,el ,salvador4 ,subgenus ,heterogeomys ,merriam #ahie4 ,heterogeomys ,merriam1 ,n4 ,amer4 ,fauna1 #h3agi1 ,january #ba4 ,type4--,geomys hispidus ,le ,conte1 #aheb1 from near ,jalapa1 ,veracruz4 ,chronologic range4--,late ,pleistocene1 ,wisconsin deposits 7,san ,josecito ,cave local fauna1 ,nuevo ,len7 to the ,recent4 ,description4--,skull dolichocephalic 7less so than in the other subgenera72 zygomata more widely spreading than in ,orthogeomys2 ramus and angular process short2 interorbital area noticeably constricted2 frontals between orbits neither exceptionally broad or inflated2 mesopterygoid fossa extending to level of posterior margin of ,m#c2 ,i having sulcus on inner third of anterior surface usually narrower than in subgenus ,orthogeomys2 enamel plate on posterior wall of ,p#d restricted to lingual half of loph2 ,m#c distinctly biprismatic1 posterior loph usually circumscribed by shallow inner re-entrant fold and outer deep fold well developed in all members of genus2 posterior loph forming conspicuous heel longer than in subgenus ,orthogeomys2 occlusal length equal to or slightly less than combined lengths of ,m#a-b2 hair coarse and hispid but never so sparse as to impart appearance of nakedness4 ,referred species and subspecies4--,eleven taxa3 99,orthogeomys onerosus 7,russell1 #aifj74 ,univ4 ,kansas ,publ41 ,mus4 ,nat4 ,hist41 #i 7#ba73edd1 ,january #ad4 ,type from ,san ,josecito ,cave local fauna1 ,upper ,pleistocene1 ,nuevo ,len4 ,orthogeomys hispidus cayoensis 7,burt1 #aicg74 ,occ4 ,papers ,mus4 ,zool41 ,univ4 ,michigan1 #cfe3a1 ,december #af4 ,type from ,mountain ,pine ,ridge1 #ab mi4 ,s ,el ,cayo1 ,british ,honduras4 ,orthogeomys hispidus chiapensis 7,nelson and ,goldman1 #aibi74 ,proc4 ,bio4 ,soc4 ,washington1 #db3aea1 ,march #cj4 ,type from ,tenejapa1 #af mi4 ,,ne ,san ,cristobal1 ,chiapas4 ,orthogeomys hispidus concavas 7,nelson and ,goldman1 #aibi74 ,proc4 ,biol4 ,soc4 ,washington1 #db3adh1 ,march #cj4 ,type from ,pinal de ,amoles1 ,quertaro4 ,orthogeomys hispidus hispidus 7,le ,conte1 #aheb74 ,proc4 ,acad4 ,nat4 ,sci4 ,philadelphia1 #f3aeh4 ,type from near ,jalapa1 ,veracruz4 ,orthogeomys hispidus latirostris 7,hall and ,alvarez1 #aifa74 ,anal4 ,escuela ,nac4 ,ciencias ,biol41 #aj3aba1 ,december #bj4 ,type from ,hacienda ,tamiahua1 ,cabo ,rojo1 ,veracruz4 ,orthogeomys hispidus negatus 7,goodwin1 #aiec74 ,amer4 ,mus4 ,novit41 #afbj3a1 ,may #d4 ,type from ,gomez ,ferias1 #acjj ft41 about #de mi4 ,s ,ciudad ,victoria1 #aj km4 ,w ,pan ,american ,highway1 ,tamaulipas4 ,orthogeomys hispidus tehuantepecus 7,goldman1 #aici74 ,jour4 ,washington ,acad4 ,sci41 #bi3agd1 ,april #ae4 ,type from mountains #ab mi4 ,,nw ,santo ,domingo and about #fj mi4 ,n ,tehuantepec1 #afjj ft41 ,oaxaca4 ,orthogeomys hispidus torridas 7,merriam1 #ahie74 ,n4 ,amer4 ,fauna1 #h3ahc1 ,january #ca4 ,type from ,chichicaxtle1 ,veracruz4 ,orthogeomys hispidus yucatanensis 7,nelson and ,goldman1 #aibi74 ,proc4 ,biol4 ,soc4 ,washington1 #db3aej1 ,march #cj4 ,type from ,campeche1 ,campeche4 ,orthogeomys lanius 7,elliot1 #aije74 ,proc4 ,biol4 ,soc4 ,washington1 #ah3bce1 ,december #i4 ,type from ,xuchil1 ,veracruz4 ,subgenus ,macrogeomys ,merriam #ahie4 ,macrogeomys ,merriam1 ,n4 ,amer4 ,fauna1 #h3ahe1 ,january #ca4 ,type4--,geomys heterodus ,peters1 #ahfe1 from ,costa ,rica1 exact locality unknown4 ,chronologic range4--,known only from the ,recent4 ,description4--,skull dolichocephalic in varying degree 7overlapping subgenera ,orthogeomys and ,heterogeomys in this respect72 mandibles elongated1 not spreading far laterally2 angular processes decidedly short2 breadth across zygomata in no instance significantly exceeding mastoid breadth2 interorbital area strongly constricted2 frontals between orbits slightly inflated laterally 7especially in forms having more strongly dolichocephalic skulls72 postorbital prominence conspicuous2 anterior margin of mesopterygoid fossa terminating well behind ,m#c2 ,i having narrow and deep sulcus entirely on inner third of anterior surface2 enamel plate on posterior wall of ,p#d restricted to inner half of loph2 ,m#c bilophodont 7outer and inner re-entrant folds each circumscribing a loph71 posterior loph remarkably elongated and forming pronounced heel1 length of crown more than combined lengths of ,m#a-b2 hair wooly in some individuals1 harsh in others but seldom hispid1 never so sparse as in subgenus ,orthogeomys2 some species having white markings1 especially on lumbar region and head4 ,referred species and subspecies4--,eleven taxa3 ,orthogeomys heterodus cartagoensis 7,goodwin1 #aidc74 ,amer4 ,mus4 ,novit41 #abbg3b1 ,april #bb4 ,type from ,paso ,ancho1 ,province ,cartago1 ,costa ,rica4 ,orthogeomys heterodus dolichocephalus 7,merriam1 #ahie74 ,n4 ,amer4 ,fauna1 #h3ahi1 ,january #ca4 ,type from ,san ,jos1 ,costa ,rica4 ,orthogeomys heterodus heterodus 7,peters1 #ahfe74 ,monatsb4 preuss4 ,acad4 ,wiss41 ,berlin1 #ahfe3agg4 ,type from ,costa ,rica1 exact locality unknown4 ,orthogeomys cavator nigrescens 7,goodwin1 #aidc74 ,amer4 ,mus4 ,novit41 #abbg3c1 ,april #bb4 ,type from ,el ,muneco 7,ro ,navarro71 #aj mi4 ,s ,cartago1 #djjj ft41 ,province ,cartago1 ,costa ,rica4 ,orthogeomys cavator pansa 7,bangs1 #aijb74 ,bull4 ,mus4 ,comp4 ,zool41 #ci3dd1 ,april4 ,type from ,bogava 7 ,bugaba71 #fjj ft41 ,chiriqu1 ,panam4 ,orthogeomys dariensis 7,goldman1 #aiab74 ,smithsonian ,misc4 ,coll41 #fj7b73h1 ,september #bj4 ,type from ,cana1 #bjjj ft41 mountains of eastern ,panam4 ,orthogeomys underwoodi 7,osgood1 #aica74 ,field ,mus4 ,nat4 ,hist41 ,publ4 #bie1 ,zool4 ,ser41 #ahe3adc1 ,aug4 #c4 ,type from ,alto de ,jabillo ,pirris1 between ,san ,geronimo and ,pozo ,azul1 western ,costa ,rica4 ,orthogeomys cherriei carlosensis 7,goodwin1 #aidc74 ,amer4 ,mus4 ,novit41 #abbg3c1 ,april #bb4 ,type from ,cataratos1 ,san ,carlos1 ,alajuela1 ,costa ,rica4 ,orthogeomys cherriei cherriei 7,j4 ,a4 ,allen1 #ahic74 ,bull4 ,amer4 ,mus4 ,nat4 ,hist41 #e3ccg1 ,december #af4 ,type from ,santa ,clara1 ,costa ,rica4 ,orthogeomys cherriei costaricensis 7,merriam1 #ahie74 ,n4 ,amer4 ,fauna1 #h3aib1 ,january #ca4 ,type from ,pacuare1 ,costa ,rica4 ,orthogeomys matagalpae 7,j4 ,a4 ,allen1 #aiaj74 ,bull4 ,amer4 ,mus4 ,nat4 ,hist41 #bh3ig1 ,april #cj4 ,type from ,pea ,blanca1 ,matagalpa1 ,nicaragua4 ,genus ,pappogeomys ,merriam #ahie4 ,pappogeomys ,merriam1 ,n4 ,amer4 ,fauna1 #h3ade1 ,january #ca4 #ahie4 ,cratogeomys ,merriam1 ,n4 ,amer4 ,fauna1 #h3aej1 ,january #ca4 ,type3 ,geomys merriami ,thomas4 #ahie4 ,platygeomys ,merriam1 ,n4 ,amer4 ,fauna1 #h3afb1 ,january #ca4 ,type3 ,geomys gymnurus ,merriam2 ,hooper1 ,jour4 ,mamm41 #bg3cig1 ,november #be1 #aidf4 ,type4--,geomys bulleri ,thomas1 #ahib1 from near ,talpa1 west slope ,sierra de ,mascota1 #hejj ft4 7actually about #ejjj ft471 ,jalisco4 ,chronologic range4--,late ,pliocene1 from deposits of early ,blancan age 7,benson local fauna1 ,arizona7 to the ,recent4 ,however in the ,pleistocene1 only late ,pleistocene records are known1 and ,pappogeomys has not been found in early 7late ,blancan7 or middle 7,irvingtonian7 ,pleistocene local faunas4 ,presumably the genus was restricted to ,mxico during the ,pleistocene until post-,wisconsin time4 ,description and discussion4--,the size ranges from as little as in the smaller kinds of ,thomomys to the maximum attained in the subfamily and matched elsewhere perhaps in only a few of the larger subspecies of ,orthogeomys grandis4 ,depending on the species and subgenus1 the form of the skull varies from generalized to specialized4 ,the generalized skulls are short and not especially narrow2 the zygomatic arches are spread laterally so far that the breadth across them exceeds the breadth across the mastoid processes4 ,the most specialized skulls are platycephalic and the breadth across the mastoid processes equals or exceeds the breadth across the zygomatic arches 7even so1 the zygomatic arches are still relatively widespread74 ,in correlation with the great breadth of the posterior part of the cranium1 the rami of the mandibles diverge widely posteriolaterally and the angular processes are remarkably elongated4 ,the rostrum is moderately broad in most species1 but not nearly so broad and heavy as in ,orthogeomys4 ,the single deep1 median sulcus on the outer surface of the upper incisor is slightly displaced to the inner side of the tooth4 ,the posterior surface of ,p#d lacks enamel 7small vestige found on lingual end of posterior wall in only two adult individuals--,,ua #cbfj and ,,ku #ajjddb1 of the subgenus ,pappogeomys72 the other three plates are fully developed as usual4 ,the p#d is provided with four fully developed enamel plates1 in the pattern characteristic of the tribe ,geomyini4 ,in the p#d of the late ,pliocene species 7,p4 bensoni7 the re-entrant angles are open 7obtuse71 a trait that is evidently primitive in the ,geomyini4 ,all three lower molars are single1 compressed1 elliptical columns with enamel on only the posterior surfaces4 ,m#a and ,m#b are also elliptical in cross-section and decidedly anteroposteriorly compressed1 like the lower molars4 ,nevertheless1 the enamel pattern is variable2 enamel plates may be retained completely across both the anterior and posterior walls of ,m#a and ,m#b or only the anterior plate may be retained without reduction and the posterior plate may be reduced so that only a vestige is retained on the lingual fourth of the tooth or the posterior plate may be completely lost4 ,m#c tends to remain at least incompletely bilophodont by reason of retaining a permanent labial re-entrant fold in most species 7with exceptions in ,pappogeomys bulleri and some old adults of ,p4 castanops74 ,primitively the occlusal surface of ,m#c is subtriangular 7subgenus ,pappogeomys71 but in the castanops species-group of the advanced subgenus ,cratogeomys1 the posterior loph usually is reduced and the occlusal surface is quadriform or obcordate4 ,curiously1 the trend towards reduction of the posterior loph is reversed in one subspecies 7,p4 merriami fulvescens7 and1 the loph has elongated into a pronounced heel in some specimens1 resembling the condition in ,orthogeomys4 ,the entire range of variation occurs in ,p4 m4 fulvescens4 ,the subtriangular pattern is retained in the most specialized species of ,cratogeomys where that pattern is associated with extreme platycephaly in the gymnurus species-group4 ,in most species the posterior loph supports two lateral plates1 the outer one always bordering the labial re-entrant fold4 ,in ,pappogeomys bulleri and in the castanops species-group1 the outer re-entrant fold of ,m#c tends to be obsolete1 and the tooth becomes quadriform or suborbiculate in some individuals and loses the bilophodont pattern that characterizes other species4 ,the lingual enamel plate is displaced to the posterior surface of the tooth1 and one or both plates may disappear with advancing age4 ,consequently1 only the anterior enamel plate remains in some adults1 and constitutes the maximum degree of reduction of enamel on ,m#c in the ,geomyinae4 ,in many adults of ,pappogeomys bulleri1 the enamel investment of the posterior loph is complete and the two lateral plates are connected1 without interruption around the posterior apex of the tooth1 evidently representing the retention of a primitive character of the ancestral lineage4 ,the m#c of ,p4 bensoni from the late ,pliocene is distinguished by minute lateral inflections suggesting the primitive biprismatic pattern4 ,also the posterior enamel plates of m#a and m#b are remarkably long1 extending around the ends of the tooth4 ,the associated upper incisor was unisulcate as in the modern species1 and the basitemporal fossa of the mandible is well developed and deep4 ,the lower jaw is stout and relatively short4 ,the masseteric ridge is well developed and has an especially thick crest4 ,the basitemporal fossa is deep4 ,in most living species1 the pelage is soft and dense1 but in one species1 ,pappogeomys fumosus1 the hairs are coarse and hispid somewhat as in ,orthogeomys4 ,key to the ,subgenera of ,pappogeomys ,a ,enamel plates completely developed across posterior walls of ,m#a and ,m#b1 except in one species 7,p4 alcorni7 having enamel restricted to lingual fourth in ,m#a2 sagittal crest lacking owing to impressions of temporal muscles remaining separated 7even in old adults72 zygomata slender1 and without platelike expansion at lateral angle4 ,subgenus ,pappogeomys p4 #ecd ,a ,enamel lacking on posterior walls of ,m#a and ,m#b2 pronounced sagittal crest developed in adults of both sexes by union of temporal impressions at middorsal line2 zygomata stout and wide1 with lateral angle expanded into broad plate4 ,subgenus ,cratogeomys p4 #ece ,subgenus ,pappogeomys ,merriam #ahie4 ,pappogeomys ,merriam1 ,n4 ,amer4 ,fauna1 #h3ade1 ,january #ca4 ,type4--,geomys bulleri ,thomas1 #ahib1 from near ,talpa1 west slope ,sierra de ,mascota1 #hejj ft4 7actually about #ejjj ft471 ,jalisco4 ,chronologic range4--,late ,pliocene 7,benson local fauna1 ,arizona7 to ,recent1 but no specimens known from ,pleistocene4 ,description4--,small1 approximately same size as small subspecies of ,thomomys umbrinus but forefeet larger and claws longer2 skull of generalized shape1 broad1 relatively short1 smoothly rounded1 not especially compressed dorso-ventrally2 zygomatic breadth great but not exceeding mastoid breadth2 zygomata relatively slender for geomyid and lacking platelike expansions at lateral angles2 rostrum relatively narrow2 sagittal crest lacking1 owing to impressions of temporal muscles remaining separated2 angular process of mandible not especially elongated2 enamel plates extending completely across posterior wall of ,m#a and ,m#b1 except in one species1 ,p4 alcorni1 where posterior plate of ,m#a remains only on lingual fourth of posterior wall 7remainder of plate lacking72 with wear1 plates sometimes exceptionally thin completely across posterior face of ,m#b and especially ,m#a in a few individuals of ,p4 bulleri much as ,paulson 7#aifa3ach-aci7 describes in extinct ,geomys tobinensis2 one or both plates rarely disappear in final stages of attrition in old individuals resulting in same dental pattern found in ,cratogeomys2 ,m#a and ,m#b retaining enamel plate on anterior wall throughout life2 ,m#c usually subtriangular in cross-section but sometimes suborbiculate or ovoid1 crown slightly bilophodont owing to shallowness of labial re-entrant angle in modern species2 posterior loph of ,m#c not especially elongated and crown not significantly longer than wide2 both lateral enamel plates of ,m#c usually well developed and approximately equal in length1 occasionally plates reduced in length and rarely one or both plates are lost with wear in old individuals2 patch of whitish or buffy hairs surrounding nose of most individuals4 ,the primitive character of the lower dentition1 as described in the species account above1 suggest that ,cratogeomys ,pappogeomys bensoni ,gidley should be referred to the subgenus ,pappogeomys rather than ,cratogeomys4 ,only the upper dentition would make positive identification possible2 however1 reference to the subgenus ,pappogeomys seems to be the best arrangement at this time4 ,referred species4--,three 7one extinct73 99,pappogeomys bensoni 7,gidley71 #aibb4 ,u4 ,s4 ,geol4 ,surv4 ,prof4 ,papers1 #aca3abc4 ,type from ,benson local fauna 7late ,pliocene71 ,cochise ,county1 ,arizona4 ,pappogeomys alcorni ,russell1 #aieg4 ,univ4 ,kansas ,publ4 ,mus4 ,nat4 ,hist41 #i7aa73cei4 ,type from #d mi4 ,w ,mazamitla1 ,jalisco4 ,pappogeomys bulleri ,thomas1 #ahib4 ,ann4 ,mag4 ,nat4 ,hist41 ,ser4 #f1 vol4 #aj3aif1 ,august4 ,type from near ,talpa1 west slope of ,sierra ,madre de ,mascota1 ,jalisco4 ,subgenus ,cratogeomys ,merriam #ahie4 ,cratogeomys ,merriam1 ,n4 ,amer4 ,fauna1 #h3aej1 ,january #ca4 #ahie4 ,platygeomys ,merriam1 ,n4 ,amer4 ,fauna1 #h3afb1 ,january #ca4 ,type3 ,geomys gymnurus ,merriam1 #ahib4 ,type4--,geomys merriami ,thomas1 #ahic1 from ,southern ,mxico1 probably in ,valley of ,mxico4 ,chronologic range4--,late ,pleistocene1 from ,wisconsin deposits 7,san ,josecito ,cave1 ,nuevo ,len1 ,upper ,bercerra1 ,mxico1 and ,burnet ,cave1 ,new ,mexico1 local faunas7 to the ,recent4 ,description4--,size medium to large2 skull becoming angular and rugose with age1 and tending towards platycephaly and dorso-ventral compression2 zygomata stout1 each bearing platelike expansion at anterolateral angle into which anterior end of jugal becomes morticed2 breadth across zygomata great relative to length of skull2 rostrum relatively broad2 squamosals expanding medially with age eventually growing over lateral parts of parietals1 and sometimes also expanding laterally displacing postglenoid notch2 sagittal crest well developed in adults of both sexes1 but especially high and bladelike in males2 lambdoidal crest prominent in all but young animals1 having dorsal outline broadly convex posteriorly in most species but strongly sinuous in gymnurus-group2 enamel plate on posterior wall of ,p#d absent2 enamel plates present only on anterior walls of ,m#a and ,m#b2 ,m#c variform in occlusal shape 7as described in species account71 either subtriangular 7gymnurus-group71 quadriform or obcordate 7castanops-group1 with exceptions as noted before72 lateral plates of ,m#c usually present in all species1 labial plate approximately as long as lingual plate in gymnurus-group 7like that in subgenus ,pappogeomys7 or distinctly shorter in castanops-group 7labial plate scarcely extending beyond border of labial re-entrant fold72 one or both lateral plates tending to disappear with wear in castanops-group1 with lingual plate usually disappearing first2 breadth across angular processes clearly more than breadth across zygomatic processes1 especially in gymnurus-group4 ,remarks4--,in the species of the castanops-group the skulls can be spoken of as generalized and the least platycephalic of the subgenus4 ,indeed1 the species of the castanops-group are hardly more specialized in this respect than is the subgenus ,pappogeomys4 ,in these skulls the breadth across the squamosal processes is less than that across the zygomatic arches1 although the two dimensions are almost equal in some examples of ,p4 merriami of the castanops-group 7where squamosal breadth varies from #he to #ih of zygomatic breadth74 ,in the species having marked platycephalic skulls 7gymnurus species-group7 the breadth across the squamosal processes equals or exceeds the breadth across the zygomatic arches 7squamosal breadth rarely #ig to #ii of zygomatic breadth71 except in ,p4 zinseri and ,p4 tylorhinus zodius4 ,the variable character of the third upper molar as between species suggests that this tooth is presently undergoing active evolution4 ,the structure of this tooth1 although differing between taxa1 is remarkably stable in other kinds of ,geomyini4 ,the most remarkable modification of ,m#c in ,cratogeomys is the obcordate pattern developed in ,p4 merriami of the castanops-group4 ,the posterior loph and entire tooth is shortened somewhat resembling in shape that of ,thomomys4 ,moreover1 the posterior loph is twisted labially2 consequently1 its posterior surface now forms the labial border of the weakly defined posterior loph4 ,owing to the torsion1 the lingual enamel plate has been rotated to the posterior surface of the tooth4 ,therefore1 the tooth is provided with two transverse enamel plates1 including the plate on the anterior wall of the tooth4 ,the labial plate is greatly reduced1 its total surface being restricted to the small labial inflection4 ,the highly specialized obcordate ,m#c is not found in the most specialized platycephalic skulls characteristic of the gymnurus species-group4 ,instead the gymnurus-group retains the primitive subtriangular pattern without significant modification4 ,referred species4--,seven3 castanops species-group ,pappogeomys castanops 7,baird1 #aheb74 ,report ,stanbury's ,exp'd4 to ,great ,salt ,lake1 p4 #cac1 ,june4 ,type from ,prairie road to ,bent's ,fort1 near present town of ,las ,animas1 ,colorado4 ,pappogeomys merriami 7,thomas1 #ahic74 ,ann4 ,mag4 ,nat4 ,hist41 ser4 #f1 #ab3bga1 ,october4 ,type from southern ,mexico1 probably ,valley of ,mxico 7see ,merriam1 #ahie3aeb74 gymnurus species-group ,pappogeomys fumosus 7,merriam1 #ahib74 ,proc4 ,biol4 ,soc4 ,washington1 #g3afe1 ,september #bi4 ,type from #c mi4 ,w ,colima1 ,colima4 ,pappogeomys gymnurus 7,merriam1 #ahib74 ,proc4 ,biol4 ,soc4 ,washington1 #g3aff1 ,september #bi4 ,type from ,zapotlan 7,ciudad ,guzman71 ,jalisco4 ,pappogeomys neglectus 7,merriam1 #aijb74 ,proc4 ,biol4 ,soc4 ,washington1 #ae3fh1 ,march #bb4 ,type from ,cerro de la ,calentura1 about #h mi4 ,,nw ,pinal de ,amoles1 ,quertaro4 ,pappogeomys tylorhinus 7,merriam1 #ahie74 ,n4 ,amer4 ,fauna1 #h3afg1 ,january #ca4 ,type from ,tula1 ,hidalgo4 ,pappogeomys zinseri 7,goldman1 #aici74 ,jour4 ,mamm41 #bj3ia1 ,february #ae4 ,type from ,lagos1 ,jalisco4 ,,phylogeny ,,of ,,the ,,geomyidae ,the fossil record of the ,geomyidae provides a sequence of morphotypes1 each representing a stage in the phyletic development of the family4 ,most of the preserved specimens probably represent the stufenreihe rather than the ahnenreihe1 as ,simpson 7#aiec3bai-bbj7 points out4 ,even so1 the stufenreihe closely approximates the general trend of evolution1 and the level of structural organization in the different stages of phyletic development may be ascertained4 ,the actual ancestral series of most lineages probably will remain unknown1 but hopefully some of the existing gaps will be filled by future discoveries4 ,from the established record1 several clearly defined lineages can be distinguished2 in fact the sequence of origin1 pattern of evolution1 and specializations1 of the principal lineages are reasonably well expressed4 ,primitive ,morphotype ,in the earliest known geomyids from the ,upper ,oligocene and ,lower ,miocene1 the premolars and molars are biprismatic and bilophodont4 ,in rodents1 this is itself a specialized pattern1 and is thought to have evolved from a more primitive sextituberculate prototype by the union of individual cusps1 and probably also cuspules1 forming the two transverse enamel lophs4 ,the primitive1 common ancestor of the ,geomyidae and ,heteromyidae with sextituberculate teeth in the early ,tertiary is unknown4 ,as soon as geomyids attained the early bilophodont stage of evolution1 the basic morphological structure of the family was established4 ,the family probably first became clearly distinguished from other ,geomyoidea at this stage4 ,in the early bilophodont stages of evolution1 owing to the relatively deep valley between them1 the two columns probably failed to unite in the normal cycle of wear1 as they do in all later geomyids4 ,griphomys described by ,wilson 7#aidj3ic7 from the late ,eocene of ,california1 has a bilophate pattern in which the anterior and posterior lophs are separated by a persistent transverse valley4 ,the occlusal pattern of ,griphomys closely resembles a stage through which the ancestors of the early ,miocene geomyids must have passed in their pre-,miocene evolution1 as ,wilson suggests 7#aidi3aae-aaf74 ,although he 7#aidj3ie2 #aidi3aaj-aah7 tentatively referred ,griphomys to the superfamily ,geomyoidea and ,simpson 7#aide3hj7 went so far as to refer it to the family ,geomyidae1 with a notation of incertae sedis1 its exact relationship to the pocket gophers is uncertain4 ,however1 the structure of the molariform dentition of ,griphomys does not exclude it from the phyletic ancestry of the ,geomyidae4 ,in subsequent stages of evolution the anterior and posterior columns become united4 ,thereby part of the valley floor between the transverse prisms was progressively elevated1 to the stage where attrition on the occlusal surface would unite the two columns4 ,on the unworn enamel cap of living geomyids the two transverse enamel folds are separated by a shallow but well defined valley1 briefly reflecting the ancient ancestral pattern4 ,union of the lophs may have been either at the mid-points of the two columns or at the edge of their protomeres4 ,a protomere is the half of a tooth containing the protocone or protoconid--lingual side of upper tooth and labial side of lower tooth4 ,the paramere is the opposite half of a given tooth--labial side of upper tooth and lingual side in lower tooth4 ,see ,miller and ,gidley1 #aiah3dcd4 ,union of the columns at the mid-points would have produced the figure-#h occlusal pattern 7or ,h-pattern71 which is characteristic of the early ,miocene ,geomyinae 7,dikkomys74 ,union of the two columns at the protomeres would have produced the ,u-shaped pattern of the ,entoptychinae1 which also occurred in the early ,miocene and were contemporary with the earliest ,geomyinae4 ,since pre-,miocene geomyids are unknown1 the actual phyletic development of the dentition is a matter of speculation4 ,probably the development of the two divergent lineages1 one leading to the ,entoptychinae and the other to the subfamily ,geomyinae1 occurred in the ,oligocene 7as depicted in ,fig4 #c74 ,of the two lineages1 the subfamily ,geomyinae1 in my view1 is the more primitive and less specialized4 ,support for this view is furnished by a reconstruction of the pattern of occlusal wear in ,dikkomys and ,pliosaccomys1 especially on the first and second molars4 ,in ,dikkomys1 the anterior and posterior column first unite near their mid-points in the first stages of wear thus producing a figure-#h shaped 7,h-shaped7 occlusal pattern in the premolar and all three molars4 ,evidently in the first two upper molars1 the columns unite closer to their lingual margins than their mid-points1 but at any rate both outer and inner re-entrant folds are evident at this stage of wear4 ,with continued attrition on m#a and m#b of ,dikkomys1 the anterior and posterior columns secondarily unite at the edge of their labial margins thus enclosing a fossette of enamel in the labial half of the tooth4 ,the lateral coalescence at the ends of the protomeres occurs because of the shallow vertical depth of the labial re-entrant fold1 and the fossette itself does not reach the base of the crown and with continued wear it too would disappear1 but not until the last stages of wear1 at least in ,dikkomys matthewi4 ,the lingual re-entrant fold is deep1 and therefore1 persistent through all stages of wear4 ,although the amount of wear required for its effacement would be great1 the occlusal configuration of the first and second lower molars in ,dikkomys could be eventually ground down to a ,u-pattern as in the entoptychids4 ,only one upper molar of ,dikkomys1 the first1 has been recovered 7see ,wood1 #aicf3bc1 fig4 #cb;,b74 ,although the tooth is in an early stage of wear1 the lingual valley is minute4 ,less attrition than required in m#a and m#b would progressively reduce the lingual fold until it too would essentially form a ,u-pattern1 perhaps retaining a slight lingual inflection4 ,hence1 the first upper molar becomes a mirror image of the first lower molar1 and the second upper molar probably had the same pattern as the first 7at least it does so in ,pliosaccomys74 ,both of the lateral re-entrant folds of the premolar are deep vertically1 and consequently would not disappear with occlusal wear4 ,therefore1 the ,h-pattern of the premolars is retained throughout life4 ,the m#c 7,m#c unknown for ,dikkomys or ,pliosaccomys7 also has deep lateral folds2 hence1 it too retains the ,h-pattern in all stages of attrition1 although the isthmus between the two prisms may become wider in the final phases of wear 7as it does in ,pliosaccomys74 ,in ,pliosaccomys1 the stages of wear are essentially the same as those described for ,dikkomys1 except that the anterior and posterior loph of the first and second molars tend to unite closer to one side of the tooth1 lingual side in upper molars and labial in lower4 ,only a slight inflection of the re-entrant fold is evident on the side of union1 and the inflection disappears in the first phases of wear as the columns unite4 ,concomitant with the lateral shift in the initial point of coalescence of the transverse lophs1 the occlusal penetration of the re-entrant fold from the opposite side increases in horizontal depth1 and the fold extends medially more than half way across the occlusal surface1 thus forming a pattern essentially like that of the entoptychids4 ,the ,u-pattern in ,pliosaccomys appears in the initial stages of wear without going through an earlier ,h-pattern as is the case in its ,miocene ancestors of the genus ,dikkomys1 unless the minute inflection is considered as indicative of that stage4 ,the two columns of the premolar and m#c are joined near their mid-points as in ,dikkomys2 therefore1 they retain their primitive ,h-pattern1 a feature unique to the ,geomyinae4 ,the evolutionary trend toward an ontogenetically earlier ,u-pattern in the first two molars in the primitive lineage of the ,geomyinae suggests that the ,u-pattern characteristic of the ,entoptychinae was simply an earlier tendency toward the same specialization that occurred later in the subfamily ,geomyinae4 ,if so1 early entoptychines would have been characterized by an ,h-pattern in the first stages of attrition1 like ,dikkomys1 and later developed union at the edge of the protomeres4 ,however1 in the entoptychines1 all the molariform dentition1 and not merely the first and second molar1 became specialized2 consequently the ,u-pattern was produced on the occlusal surfaces of each of the cheek teeth4 ,as in ,pliosaccomys1 the transitional phase1 in which the two columns were united at their mid-points1 was eventually eliminated from the pattern of wear and only the ,u-pattern1 that now appeared in the initial stages of wear1 was retained4 ,in the entoptychines of the early ,miocene there is no suggestion of the ,h-pattern that characterizes the ,geomyinae1 except in the position of the cusps before wear in the lower molars of ,pleurolicus sulcifrons1 which1 according to ,wood 7#aicf3f71 suggests the ,h-pattern4 ,in earlier unknown ,oligocene stages of evolution1 the prisms possibly united first at their mid-points1 and the columns may have joined at the side of the tooth only in the terminal stages of wear4 ,the ,u-pattern of pre-,miocene entoptychines1 therefore1 may have become the dominant occlusal pattern only in the later stages of phyletic development4 ,according to the recently expressed views of several paleontologists1 the ,entoptychinae constitute the primitive lineage of the family and the early ,geomyinae constitute a specialized offshoot of the entoptychine ancestral assemblage4 ,the structure of the ,entoptychinae1 especially of the less advanced genera1 closely approximates that of the hypothetical primitive morphotype4 ,but1 according to my view1 the subfamily ,geomyinae constitutes the ancestral assemblage and its structure is essentially that of the primitive morphotype of the family4 ,at any rate the structure of the early geomyines more closely approximates the structure of the ancestral stock than the more divergent entoptychines4 ,therefore1 the genus ,dikkomys of the early ,miocene1 the first known geomyine1 is considered to be a generalized geomyid1 and1 although it is a contemporary of the more specialized entoptychid assemblage1 is considered to be more closely allied to the ancestral stock4 ,the entoptychines were the dominant and most highly differentiated geomyids of the early and middle ,miocene4 ,nevertheless1 they became extinct in the middle ,miocene1 and the geomyines of that time survived and later gave rise to the modern pocket gophers4 ,therefore1 the early history of the family ,geomyidae is characterized by an early radiation and trend toward specialization1 followed by survival of the less specialized ,geomyinae and extinction of the more specialized ,entoptychinae4 ,entoptychid ,radiation ,the most abundant geomyids of the early and middle ,miocene1 the ,entoptychinae1 consisted of at least #bd species 7see ,wood1 #aicf3d-be7 classified in four genera3 ,pleurolicus1 ,gregorymys1 ,grangerimus1 and ,entoptychus4 ,the genera were essentially contemporaneous 7see ,figure #c74 ,even so1 the subfamily was morphologically varied1 pointing to an earlier origin in the ,oligocene 7actually a part of the ,john ,day ,fauna1 including ,pleurolicus may be correlated with late ,oligocene ,whitneyian age7 followed by a relatively rapid radiation including all four genera in the early ,miocene4 ,two genera1 ,pleurolicus and ,gregorymys1 continued into the ,middle ,miocene 7,hemingfordian74 ,this divergence1 specialization1 and subsequent radiation suggest that the entoptychines evolved into a new major adaptive zone1 in the sense described by ,simpson 7#aide3aii-bjf74 ,the radiation is correlated geographically and temporally with the southward retreat of the ,neotropical flora of the ,tertiary from the western ,united ,states and southward movement of the ,arctic flora of the ,tertiary 7see ,axlerod1 #aiej2 ,berry1 #aicg3ca-df2 ,chaney1 #aidg3aci-adh2 and ,kendeigh1 #aifa3bhj-bhc74 ,in the early ,tertiary the ,neotropical-tertiary geoflora occurred northward to at least #di latitude in western ,north ,america1 and the boreal ,arctic-tertiary flora was restricted to a circumpolar zone4 ,the southward and eastward shift of the ,neotropical-tertiary flora1 associated with the drying and chilling of the continent1 began in the middle or late ,oligocene and was concurrent with the divergence and radiation of the ,entoptychinae4 ,beginning in late ,oligocene and continuing at least into middle ,miocene1 most of the region in which the entoptychines occurred was occupied by the ,arcto-tertiary geoflora of which the temperate forest division contributed the dominate plant associations4 ,the maples1 chestnuts1 dogwoods1 beeches1 walnuts1 oaks1 elms1 birches1 and sycamores of that flora were the forerunners of today's eastern deciduous forest4 ,it is my view that the entoptychines became adapted to the conditions of this paleoecological environment and radiated rapidly in the ,arikareean when the major change occurred in climax vegetation4 ,the ancestral stock of the ,geomyinae was not so successful in the ,arcto-tertiary climax1 and most of it probably was displaced southward along with the tropical flora4 ,the skeleton in the entoptychines is not so strongly fossorial as in the modern geomyids 7,wilson1 #aidi3aag71 and these early geomyids probably were semi-fossorial with somewhat the same burrowing habits as those of the living mountain beaver 7,aplodontia74 ,inasmuch as the morphology and taxonomy of the entoptychines were discussed in detail by ,cope 7#ahhd7 and reviewed later by ,wood 7loc4 cit471 there is no need to recount the details here4 ,according to ,wood 7op4 cit41 #bg-bh71 ,pleurolicus occupied a central position in the entoptychid radiation and perhaps appeared slightly earlier than the other genera4 ,wilson 7#aidi7 suggested that the lower part of the ,john ,day may actually be ,upper ,oligocene rather than ,lower ,miocene1 and this arrangement is followed here4 ,also1 ,pleurolicus is less specialized than the other genera and occurs in deposits of both the ,great ,plains and the ,pacific ,coast4 ,gregorymys1 also little specialized1 occurred only on the ,great ,plains4 ,the more specialized genera1 ,grangerimus and ,entoptycus1 evidently appeared somewhat later than ,pleurolicus and evolved from it4 ,except for a record from southern ,texas reported recently by ,hibbard and ,wilson 7#aiej3fba-fbc7 and the new species described by ,mac,donald 7#aifc3ahb7 from the ,sharps ,formation of ,south ,dakota 7early ,arikareean71 ,grangerimus is known only from the ,pacific coast4 ,entoptycus was restricted to the ,pacific ,coast 7,john ,day fauna74 ,entoptycus is the most specialized of the known genera2 it has pronounced fossorial adaptations1 especially in the skull4 ,its molariform teeth are rootless and ever-growing as in the modern geomyines4 ,moreover1 the continuous enamel bands on only moderately worn teeth become separated in the final stages of wear into anterior and posterior enamel plates by tracts of dentine that extend toward the crown on the sides of each tooth4 ,this extension was made possible by the union of the two columns at both the lingual and labial margins of the tooth forming an ,o-pattern1 and the crown is essentially monoprismatic save for the isolated enamel fossette in the center of the tooth4 ,the fossette is all that remains of the lateral re-entrant fold that characterized the preceding ,u-pattern of the earlier stages of wear4 ,late in the sequence of wear1 the anterior enamel plate is lost in the lower molars and the posterior plate in the upper molars4 ,the ,u-pattern characterizes the final stages of attrition in the other genera of the ,entoptychinae2 none developed the dental specializations seen in ,entoptycus4 ,rootless1 ever-growing cheek teeth1 discontinuous enamel patterns1 and monoprismatic molars were not evolved in the subfamily ,geomyinae until the late ,pliocene4 ,phyletic ,trends in ,subfamily ,geomyinae ,the subfamily ,geomyinae is made up of three groups1 recognized taxonomically for the first time in this account as tribes--,dikkomyini1 ,thomomyini1 and ,geomyini 7for full discussion of classification1 see previous account74 ,the phylogeny proposed by me is illustrated in ,figure #c4 ,the tribe ,dikkomyini is characterized by generalized and primitive features that together form the basic structural foundation of the subfamily4 ,evolution within the ,dikkomyini resulted in the acquisition and perfection of fossorial adaptations4 ,the ,thomomyini and ,geomyini are considerably more specialized than the ancestral ,dikkomyini from which they evolved4 ,the ,geomyini are clearly more specialized than the ,thomomyini1 suggesting closer affinity between the ,thomomyini and the ,dikkomyini than between the ,geomyini and the ,dikkomyini4 ,the specializations in the dentition and the associated changes in the skull of the ,thomomyini and ,geomyini permit more efficient mastication of fibrous vegetation4 ,along with these specializations1 fossorial adaptations inherited from the ,dikkomyini are retained without noteworthy modification4 ,dikkomys1 the earliest known genus of the tribe ,dikkomyini1 can be taken as a starting point of evolution for the subfamily ,geomyinae4 ,the ,pliocene genus ,pliosaccomys is the only other known geomyine having primitive features closely resembling those of ,dikkomys4 ,the relatively close but previously unrecognized relationship between ,dikkomys and ,pliosaccomys can be understood when patterns of wear on the occlusal surfaces of the cheek teeth are taken into account4 ,it appears that ,pliosaccomys descended from ,dikkomys-like stock1 if not ,dikkomys itself4 ,although ,dikkomys is towards the beginning of this phyletic sequence and ,pliosaccomys towards the end of the sequence1 the primitive features shared by the two provide a generalized morphotype for the subfamily ,geomyinae4 ,in the molariform dentition1 an almost complete series of stages of wear in ,pliosaccomys has been preserved1 and those of ,dikkomys can be reconstructed with reasonable accuracy from those that are known 7see ,fig4 #d73 7#a7 ,in the initial stage of wear in ,dikkomys the anterior and posterior columns are separated by an intervening valley 7,fig4 #d;,a71 and the occlusal surface of each column bears a loph of dentine surrounded by a ring of enamel3 protoloph on the anterior column and metaloph on the posterior column of the upper teeth 7protolophid and hypolophid in corresponding positions in the lower teeth74 ,actually this stage is not preserved in the known material of ,dikkomys1 but does occur in both geomyines and entoptychines in all stages of evolution1 and it must have also occurred in ,dikkomys in order for the next two stages1 which are preserved1 to have developed4 7#b7 ,the occlusal surfaces are ground down to a level where the enamel loops of the two columns join at their mid-points1 thus forming an ,h-shaped pattern 7,fig4 #d;,b71 or more exactly a pattern resembling a figure #h4 ,probably this was the primitive pattern in the final stage of wear in the geomyid ancestor of the ,oligocene4 ,illustration3 ,,fig4 #c4 ,diagram depicting geologic range and probable phyletic relationships of the family ,geomyidae4 ,dashed lines represent parts of lineages that are not represented by fossil records1 and solid lines represent parts of lineages verified by actual specimens4 ,question marks indicate uncertainty of suggested ancestry of known taxa4 ,the relationships within the subfamily ,entoptychinae are modified after ,wood 7#aicf71 and the temporal range of the ,miocene geomyids have been adjusted to agree with current stratigraphic correlations4 ,hence1 ,pleurolicus1 ,gregorymys and ,dikkomys are illustrated as ranging into the ,hemingfordian1 rather than being confined to the ,arikareean 7see ,mac,donald1 #aifc1 and ,black1 #aifa74 7#c7 ,in the pre-final stage of wear1 the anterior and posterior lophs of the first and second molars unite secondarily at the edge of their protomeres 7labial side in the lower and lingual in the upper71 thus enclosing an isolated enamel fossette 7,fig4 #d;,c74 ,lateral union occurs in the lower teeth because the vertical depth of the labial re-entrant angle is less than the depth of the lingual re-entrant fold4 ,in the upper teeth the reverse is true4 ,the re-entrant angle on one side of the premolar is as deep vertically as the angle on the other side of that tooth1 and both reach the base of the crown2 therefore1 they do not disappear at any stage of attrition4 ,the same pertains in the third lower molar4 7#d7 ,in the final stage of wear 7,fig4 #d;,d71 the enamel fossette disappears as a result of continued attrition on the occlusal surface in the upper series4 ,the fossette may vary somewhat in vertical depth in m#a and m#b1 but the amount of wear required for its effacement would be greater than in the upper teeth4 ,therefore1 upon wear1 the ,u-pattern would become characteristic of the final stage in ,m#a 7and probably also ,m#b71 but the modified ,h-pattern described in ,fig4 #d;,c would prevail in m#a and m#b4 ,perhaps1 in extremely worn teeth1 the labial fossette of m#a and m#b would disappear4 ,if this advanced stage of effacement is obtained1 then the two columns would be united across the entire surface of their protomeres from the center of the crown to its labial edge1 and the occlusal pattern would be in the shape of a ,u4 ,the occlusal pattern1 at least in ,m#a and ,m#b1 in the final stages of wear in ,dikkomys resembles that in the subfamily ,entoptychinae1 but the ,u-pattern develops on only the first and probably the second molar in ,dikkomys and not on all of the cheek teeth as it does in the entoptychines4 ,judging from the material that has been described1 the ,u-pattern did not develop in the lower teeth of ,dikkomys until the ,hemingfordian 7,d4 woodi71 upper ,rosebud1 and specimens of ,d4 matthewi from the earlier ,arikareean1 lower ,harrison1 suggest that the modified ,h-pattern1 with secondary coalescence at the edge of the protomeres1 persisted throughout life1 without developing the ,u-pattern in the final stages of wear4 ,essentially the same patterns of wear characterize the genus ,pliosaccomys1 except that the earlier stages were telescoped and the second stage was omitted while another 7final7 stage was added4 ,the stages are reconstructed in sequence in figure #d1 and all are based on preserved dentitions1 as follows3 7#a7 ,the first phases of wear produced the pattern 7,fig4 #d;,e and ,i7 described for ,dikkomys in the previous account 7,fig #d;,a74 7#b7 ,a small additional amount of wear produced the #bnd stage 7,fig4 #d;,f and ,j7 characterized by a ,u-pattern1 formed by union of the anterior and posterior columns at the edge of the protomeres of the first and second molars1 both above and below1 without first forming an ,h-shaped pattern4 ,union at the mid-points thus was omitted from the sequence of wear in these two teeth4 ,in the premolars and third molars the primitive ,h-pattern did form1 as in ,dikkomys4 ,the pattern of wear in the first two molars is the same as in the entoptychines of the early ,miocene4 ,the trend of evolution through which the ,pliosaccomys lineage passed must have featured a progressively earlier union at the edge of the tooth until the lateral coalescence occurred simultaneously with the median union4 ,at that stage1 emphasis was shifted to the union at the edge of the tooth1 and eventually the teeth failed to unite at their mid-points and the ,u-pattern developed directly4 ,therefore1 the horizontally deep re-entrant fold that separates the two lophs of the ,u-pattern is equivalent to one fold plus the apex of the opposite fold4 7#c7 ,the horizontal re-entrant fold of the ,u-pattern was remarkably shallow vertically and disappeared with little additional wear4 ,thus the two parts of ,m#a1 and also of ,m#b1 are united into a single column except for a slight inflection on the labial side and this is true also of m#a and m#b except for a slight inflection on the lingual side 7,fig4 #d;,g and ,k74 ,the inflection appears to have persisted in the upper teeth 7,fig4 #d;,h71 but evidently with slight wear1 disappeared in the lower teeth 7,fig4 #d,l74 ,the final monocolumnar pattern was attained early ontogenetically1 evidently before the permanent premolar had fully erupted2 hence1 the earlier stages occurred only in transition1 persisted for only a brief interval in the teeth of juveniles1 and the final stage developed in the young animal and lasted throughout the rest of its life in ,pliosaccomys4 ,in ,dikkomys the two columns never united into a single column1 and a bilophodont occlusal pattern persisted throughout life4 ,the early phyletic development of the subfamily ,geomyinae took place in the tribe ,dikkomyini from the early ,miocene into the early ,pliocene4 ,compared with the rapid evolution of the specializations that distinguish the ,entoptychinae1 the structural changes in the early ,geomyinae occurred at a remarkably slow rate4 ,in fact the lineage changed but little from ,dikkomys to ,pliosaccomys1 in parts of the animal that can be compared1 as illustrated by the low-crowned and rooted cheek teeth1 the continuous enamel bands1 the lack of grooving of the upper incisor1 the retention of the primitive ,h-pattern1 both above and below1 in the premolar and third lower molar1 and the ridges and fossae of the mandible to which the muscles of mastication attach4 ,the only major changes detected in the known fragments are in the pattern of wear and the final configuration of the first and second molars1 as described above4 ,the unification of the two lophs in each of these two teeth into a single column was a significant step in the evolution of the ,geomyinae1 and is a stage between the primitive bilophodont pattern of the early and middle ,miocene geomyines having continuously bicolumnar teeth and the monolophodont pattern in the modern pocket gophers of both lineages in which these teeth consist of a single column in all but the initial stages of wear4 ,the monocolumnar structure of the first and second molars in the final stages of wear1 therefore1 is closer to that in the lineage of ,thomomys than it is to that of ,dikkomys4 ,other specializations in the dentition of ,pliosaccomys1 especially in m#a and m#b where the ,h-pattern has been completely eliminated from the sequence of wear1 are too far advanced for ,pliosaccomys to have given rise to the tribe ,geomyini4 ,the teeth in the immediate ancestor of the ,geomyini must have been less specialized in m#a and m#b1 perhaps about as in ,dikkomys4 ,in the m#a and m#b of the tribe ,geomyini1 the ,h-pattern is formed in the initial stages of wear2 therefore1 in the early ,pliocene ancestor1 presently unknown in the fossil record1 the ,h-pattern probably was present4 ,even so1 the ancestor of the ,geomyini and that of ,pliosaccomys probably were closely allied otherwise1 and both probably had attained the highly specialized fossorial adaptations characterizing all modern pocket gophers1 before the divergence of ,pliosaccomys and the ,geomyini took place4 ,the evidence points to a major divergence of the geomyines that lived in the latest ,miocene or the early ,pliocene 7probably the latter7 and that gave rise to the two modern lineages1 ,thomomyini and ,geomyini 7see ,fig4 #c74 ,one1 the most primitive of the two1 gave rise to the ,thomomyini lineage that eventually evolved into ,thomomys4 ,pliosaccomys is closely allied to the ancestry of this lineage1 although it is probably not the actual ancestor1 as mentioned previously4 ,aside from the aforementioned specializations of the first and second molars1 the features of the ,thomomyini are less advanced than in the other specialized lineage 7tribe ,geomyini74 ,primitive traits retained in the tribe ,thomomyini 7and also characteristic of the ancestral tribe ,dikkomyini7 are3 7#a7 ,small size1 in general no larger than the ancestral morphotype2 7#b7 lack of grooving on the upper incisor 7although a slight rudimentary groove is developed rarely in some living species72 7#c7 retention of anterior and posterior enamel plates in lower and upper cheek teeth2 7#d7 premolars having widely open re-entrant folds2 7#e7 smooth and generalized skull lacking marked angularity1 regosity or cresting 7neither the sagittal nor the lambdoidal crest are ordinarily well developed except in ,thomomys bulbivorus72 7#f7 forefoot small1 less modified for digging than in the ,geomyini4 ,illustration3 ,,fig4 #d4 ,drawings of the molariform dentitions of ,dikkomys and ,pliosaccomys 7,tribe ,dikkomyini7 depicting the patterns of wear on the occlusal surfaces4 ,ontogenetically1 the stages of wear are arranged from left to right in each row4 ,stages not represented by actual specimens have been carefully reconstructed from information provided by known stages in the sequence of wear and the dentitions of other geomyines4 #e4 ,a-,d4 ,dikkomys woodi1 right lower tooth-row1 including p#d-m#c4 ,patterns based on ,no4 ,p#bfbhd 7,,fmnh7 from ,upper ,rosebud 7,middle ,miocene71 ,shannon ,co41 ,south ,dakota 7,b above74 ,e-,h4 ,pliosaccomys dubius1 left upper tooth-row1 including ,p#d-,m#b 7,m#c unknown74 ,patterns based on ,nos4 #agih and #agii 7,,lam7 from ,smiths ,valley 7,middle ,pliocene71 ,lyon ,co41 ,nevada4 ,i-,l4 ,pliosaccomys dubius1 right lower tooth-row1 including p#d-m#c4 ,patterns based on ,nos4 #agif 7holotype71 #ahjd1 and #ahjf 7,,lam7 from ,smiths ,valley 7,middle ,pliocene71 ,lyon ,co41 ,nevada4 ,the lineage of the ,thomomyini is essentially rectilinear and without the major branching seen in the tribe ,geomyini4 ,the one genus1 ,thomomys1 appears first in the ,upper ,pliocene 7early ,blancan time71 and the specializations characterizing the lineage had already developed by that time4 ,evidently1 the early stages of divergence from the ancestral stock resulted in the development of rootless1 ever-growing1 more hypsodont cheek teeth1 simplification of ,m#c1 and enlargement of the masseteric ridge on the mandible4 ,the enamel investment on the sides of the molariform teeth is interrupted owing to intrusion of tracts of dentine on the sides of each column4 ,even so1 complete anterior and posterior plates are retained on all of the cheek teeth 7,fig4 #e1 ,k and ,l7 and there is no trend toward additional loss of enamel as in the ,geomyini4 ,the enamel on the sides of the column has little functional value1 and its elimination probably reduces friction during the anteroposterior movements of the lower jaw1 thereby increasing the efficiency of the cutting blades on the anterior and posterior wall of the tooth4 ,the simplification of ,m#c was achieved by union of the two columns of the primitive pattern into a single column and obliteration of both the labial and lingual re-entrant folds in the first stages of wear4 ,the adult tooth 7see ,fig4 #e,l7 is without trace of the bilophate pattern and is not elongated2 therefore1 its structure is essentially the same as that of the first and second upper molars4 ,in the ,thomomyini1 the two lophs of the unworn molars unite entirely across the width of their surfaces with the first traces of wear 7see ,fig4 #e1 ,i and ,j71 owing to the shallow and uniform depth of the transverse valley4 ,in the molars1 the final pattern is acquired1 therefore1 before the deciduous premolar has been replaced by the permanent tooth4 ,a relatively shallow re-entrant inflection between the ends of the parameres sometimes is retained1 although it also will disappear with slight additional wear4 ,therefore1 both lophs tend to unite completely with the first stages of wear in the ,thomomyini1 thus omitting both ,u and ,h patterns from the sequence of wear4 ,this is the highest degree of specialization attained in the ,geomyidae in regard to the patterns of wear1 since a sequence of bilophodont patterns appear in both the ,dikkomyini and ,geomyini before the monoprismatic pattern is developed4 ,illustration3 ,,fig4 #e4 ,drawings of molariform dentitions representative of the tribes ,geomyini and ,thomomyini depicting patterns of wear on the occlusal surface4 ,a-,d represent1 in ontogenetic sequence from left to right1 upper tooth-rows of the tribe ,geomyini4 ,e-,h represent1 in the same sequence of stages1 lower tooth-rows of the tribe ,geomyini4 ,i-,l represents both upper and lower tooth-rows of both pre-final and final stages of wear in the tribe ,thomomyini4 ,all #e4 ,a and ,e4 ,geomys bursarius majusculus1 ,no4 #bidh 7,,ku71 ,douglas ,co41 ,kansas4 ,right upper 7,a7 including ,,dp#d-,m#c2 lower left 7,e7 including dp#d-m#c4 ,b and ,f4 ,pappogeomys bulleri burti1 ,no4 #ajjddd 7,,ku71 #aj mi4 ,,nnw ,barra de ,navidad1 ,jalisco4 ,right upper 7,b7 including ,p#d-,m#c2 right lower 7,f7 including p#d-m#c 7both ,p#d and p#d with unworn enamel caps74 ,c and ,g4 ,pappogeomys bulleri albinasus1 ,no4 #cajdd 7,,ku71 #aj mi4 ,s and #h mi4 ,w ,guadalajara1 ,jalisco4 ,right upper 7,c7 including ,p#d-,m#c2 right lower 7,g7 including p#d-m#c4 ,d and ,h4 ,pappogeomys bulleri albinasus1 ,no4 #cajjb 7,,ku71 ,w side ,la ,venta1 #ac mi4 ,w and #d mi4 ,n ,guadalajara1 ,jalisco4 ,right upper 7,d7 including ,p#d-,m#c2 right lower 7,h7 including p#d-m#c4 ,i and ,j4 ,thomomys talpoides bridgeri1 ,no4 #fhfe 7,,ku71 #b mi4 up ,mink ,creek1 ,pocatella1 ,bannock ,co41 ,idaho4 ,left upper 7,i71 ,,dp#d-,m#c2 left lower 7,j71 dp#d-m#c4 ,k and ,l4 ,thomomys talpoides fossor1 ,no4 #acbje 7,,ku71 ,wasson ,ranch1 #c mi4 ,e ,creede1 ,mineral ,co41 ,colorado4 ,right lower 7,k71 p#d-m#c2 left upper 7,l71 ,p#d-,m#c4 ,relationship of the ,geomyini with the ancestral ,dikkomyini is most clearly demonstrated in the sequence of wear on the occlusal surfaces of the molars4 ,as in all geomyids1 the upper part of the crown is biprismatic in the newly erupted tooth1 and the two columns are separated by an intervening valley4 ,with slight attrition on the unworn enamel cap1 the weakly developed cusps merge and form a transverse enamel loop on each of the two columns 7see third molar in ,fig4 #e1 ,a and ,e71 each loop enclosing a core of dentine that had become exposed4 ,the valley between the two columns is shallow1 and upon further wear of the tooth1 the two loops unite4 ,the two columns become joined at different points in the upper and lower molars depending on the varying depth of the valley in different teeth4 ,therefore1 upper and lower molars develop distinctly different occlusal configurations4 ,in the lower molars1 the pattern characteristic of ,dikkomys 7,fig4 #d;,c7 is preserved without significant modification1 as illustrated in an immature specimen of ,geomys 7see ,fig4 #e;,e74 ,the ,h-pattern and modified ,h-pattern are developed in the same sequence of wear in the ,geomyini4 ,a juvenal female 7not illustrated71 ,,ku #bica1 provides an example of the intermediate ,h-pattern4 ,in this specimen1 the protolophid and hypolophid of the left m#b are united only at their mid-points1 indicating that the pattern of wear occurs in the same sequence in the ,geomyini as it did in the ,miocene genus ,dikkomys4 ,after the two columns have become united at their mid-points1 a secondary union is formed at the edge of their protomeres1 thus enclosing the enamel fossette as illustrated in ,figure #e;,e 7this is the modified ,h-pattern mentioned above74 ,however1 the fossette itself is shallow and soon disappears with slight wear4 ,at this stage1 the occlusal configuration would be in a ,u-pattern 7m#a in ,fig4 #e;,e74 ,the lingual re-entrant fold is also shallow in vertical depth2 therefore1 it is obliterated by wear following the eradication of the labial fossette4 ,consequently1 the two columns are united into one4 ,in m#c 7see ,figs4 #e;,e1 ,f1 and ,g71 the two columns merge by progressive lateral expansion of the medial isthmus4 ,in the first and second upper molars1 the two columns unite across the entire surface of their protomeres from near the lingual edge of the crown to near its center4 ,a minute inner inflection may be temporarily retained in some teeth4 ,at this stage 7see ,fig4 #e;,b71 the parameres are still separated by the labial fissure1 and the occlusal pattern is in the shape of a ,u1 resembling1 but not exactly duplicating1 the pre-final pattern of ,ml and ,m#b in the genus ,pliosaccomys 7see ,fig4 #d;,h74 ,the labial fissure is shallow1 and1 with further wear1 the inflection is worn away and the parameres also unite1 thereby forming a monoprimatic crown in the final stage4 ,in ,m#c1 the two lophs first become united near the edge of their protomeres 7see ,fig4 #e;,b71 therefore forming a ,u-pattern similar to that developed in ,ml and ,m#b of ,pliosaccomys4 ,the connection of the two lophs is not directly at the end of the protomere2 consequently a shallow lingual inflection remains4 ,the lingual edge of the valley is also shallow1 and1 with continued wear a second union of the two lophs takes place near the ends of their parameres1 and the deeper1 interior part of the valley remains as an isolated enamel fossette 7see ,fig4 #e;,c74 ,the two primary lophs of the tooth are now joined near both sides1 having shallow lingual and labial re-entrant angles on the sides and the enamel island in the center4 ,with continued effacement of the occlusal surface1 the fossette will be eradicated1 and the pattern of the occlusal surface will become the partially biprismatic pattern of the final stages 7adult7 of wear 7see ,fig4 #e;,d74 ,m#c's of ,dikkomys and ,pliosaccomys are not known2 however1 it seems reasonable to assume that the pattern of wear in the ,m#c of ,dikkomyini was not essentially different from that of the ,geomyini1 except that it is likely that the ,u-pattern of the second stage of wear in the ,geomyini was probably the final stage in the genus ,dikkomys4 ,judging from the pre-final stages of wear1 the dentition of the ,geomyini provides a curious combination of patterns that resemble in part the ,miocene genus ,dikkomys and in part the early and middle ,pliocene genus ,pliosaccomys4 ,there is no significant variation in the premolars or third molars 7at least in the lower teeth7 of the ,geomyinae from the early ,miocene to late ,pliocene2 therefore1 deviations of major significance are in the character of the first and second molars4 ,in the ,geomyini1 the patterns of wear of m#a and m#b are the same as those of ,dikkomys1 and are distinctly different from those of ,pliosaccomys where the two columns first unite at the edge of their protomeres to form a ,u-pattern1 rather than at their mid-points to form an ,h-pattern4 ,even though the intermediate stages of ontogeny in m#a and m#b of ,pliosaccomys and the ,geomyini are entirely different1 the bicolumnar crowns of both eventually unite1 upon wear1 into a single column4 ,on the other hand1 the patterns of ,m#a and ,m#b in the ,geomyini most closely resemble those of ,pliosaccomys1 rather than ,dikkomys4 ,in this regard it should be pointed out that the upper molars of ,dikkomys are presently represented by only one tooth1 an ,m#a in an early stage of wear4 ,as described already1 the patterns of ,m#a-b evidently would be mirror images of m#a-b in corresponding stages of wear4 ,however1 the initial union of the two columns1 in the ,m#a that is known1 is somewhat to the lingual side of center and the relatively small lingual valley does not reach the base of the crown1 indicating1 that eventually with wear1 the two columns of ,dikkomys might have become united across the entire surface of their protomeres as in ,pliosaccomys4 ,even so1 the two columns of ,m#a do initially join closer to their mid-points than they do in ,pliosaccomys1 and1 if they did actually unite across their protomeres1 the union would have occurred with subsequent wear4 ,that is1 the first occlusal pattern would be ,h-shaped 7but with the connection closer to the lingual than the labial side71 as in m#a and m#b1 and it would become ,u-shaped only after additional wear4 ,this sequence of patterns of ,m#a and ,m#b1 as already pointed out1 does not pertain in ,pliosaccomys or the ,geomyini1 since the ,u-pattern is formed with the first union of the two columns at the edge of their protomeres1 and the primitive ,h-pattern is never developed1 unless one counts the slight lingual inflection1 that occasionally is formed just after the two columns unite1 as being indicative of the primitive pattern4 ,as in the lower teeth1 the bicolumnar crowns of early ontogeny in both ,pliosaccomys and the ,geomyini become eventually united1 with wear1 into a single column4 ,based upon the foregoing evidence1 it would seem likely that the ,geomyini evolved from an early ,pliocene 7perhaps late ,miocene7 ,dikkomyini ancestor that had evolved the specializations of ,m#a and ,m#b that characterize its relative1 ,pliosaccomys1 but had not also evolved the specializations of m#a and m#b that distinguish ,pliosaccomys4 ,therefore1 the ancestor of the ,geomyini differed from the ,pliosaccomys-,thomomyini lineage in its retention1 unmodified1 of the primitive patterns in m#a and m#b that characterized the earliest known ,geomyines 7,dikkomys74 ,the same patterns are preserved in m#a and m#b of its modern descendents1 the living ,geomyini4 ,in the ,pliosaccomys-,thomomyini lineage the pattern of m#a and m#b are entirely different1 as described above4 ,the earliest record of the ,geomyini is the extinct genus ,pliogeomys 7see ,fig4 #f7 in the latest ,hemphillian 7middle ,pliocene7 and earliest ,blancan 7late ,pliocene74 ,pliogeomys is more primitive than any modern genus of the ,geomyini1 seems to have been a late survivor of the primitive stock1 but was itself probably a collateral lineage and not on the direct line of descent4 ,the cheek teeth in ,pliogeomys are rooted and less hypsodont than in the late ,pliocene examples of the modern genera1 and the anterior enamel plate of the lower molars shows no indication of reduction1 as would be expected if ,pliogeomys were in the direct line of evolution4 ,separation of ,pliogeomys from the main stem of the ,geomyini probably occurred after several specializations had already been achieved by the ,geomyini4 ,two inheritances might have been grooving on the upper incisors and some reduction in amount of enamel on the sides of the cheek teeth4 ,the dentine tracts on the sides of the cheek teeth of ,pliogeomys are narrow 7see ,fig4 #g;,a7 and barely separate the enamel blades and there is no discernible reduction in the anterior enamel blades on its lower molars4 ,those blades evidently were lost in the main lineage before the ,pleistocene radiation of the living genera took place4 ,pliogeomys is in an intermediate stage in evolution1 and was not so advanced as was the main lineage at the time ,pliogeomys died out4 ,its structure does provide clues as to phyletic development that took place in the main lineage4 ,specialized trends in the early phylogeny of the ,geomyini included3 development of rootless1 ever-growing cheek teeth and an increase in hypsodonty2 loss of the bicolumnar structure of the first and second molars1 and1 consequently1 the formation of a single elliptical column in the final stage of wear2 interruption of the enamel investment of the molariform teeth and formation of anterior and posterior enamel plates2 and enlargement of the masseteric ridge and fossa4 ,each of these trends occurred independently in the ,thomomyini1 and each is an example of parallelism in the phyletic evolution of the two lineages4 ,three additional specializations lacking in the ,thomomyini are the grooving on upper incisors1 loss of anterior enamel plate in lower molars1 and development of a basitemporal fossa on the mandible4 ,evidently1 two grooves evolved in the ancestral incisors in the same bisculcate pattern preserved in ,pliogeomys1 ,zygogeomys and ,geomys4 ,the innermost groove is weakly developed in ,pliogeomys1 suggesting that this character was in an intermediate stage of evolution in the ancestral lineage at the time that ,pliogeomys split off4 ,numerous other specializations in the ,geomyini appeared later1 but evolved in the different genera that diverged from the ancestral lineage and are discussed separately in the next account4 ,only two of the major features characterizing the ,dikkomyini are retained in the ,geomyini3 the ,h-pattern on the occlusal surface of the m#a and m#b developed during the initial stages of wear1 and the bicolumnar pattern of ,m#c4 ,adaptive radiation produced the living genera of the ,geomyini in the late ,pliocene and early ,pleistocene 7see ,fig4 #f7 and subsequent specialization of the ancestral morphology followed4 ,parallelism in the molars of later geomyines and the ,entoptychinae is illustrated by the lateral interruption of the enamel investment and loss of enamel plates and by the omission of the ,h-pattern stage in the first and second molars 7in ,pliosaccomys74 ,resemblance of dentitions in certain stages of wear in ,pliosaccomys and in entoptychines led some investigators1 for instance1 ,hibbard 7#aiec3ceg71 to suggest that ,pliosaccomys descended from one of the less specialized entoptychines1 possibly ,grangerimus but probably ,gregorymys4 ,actually1 the highly specialized upper and lower premolars and third molars of the entoptychines rule them out as ancestors of the later geomyines4 ,the evolution of entoptychine-like features in ,pliosaccomys is regarded as an example of iteration1 a pattern of parallelism 7see ,simpson1 #aiec3bdh-bec7 where an allochronic and independent lineage undergoes the same evolutionary trend that phyletically characterized an earlier lineage1 usually after the latter has become extinct4 ,in this case1 the lineage giving rise to ,pliosaccomys passed through the same phyletic stages in its evolution in the early ,pliocene 7and possibly the late ,miocene7 as did the entoptychines in the late ,oligocene and early ,miocene4 ,another parallelism by iteration1 occurring in the middle and late ,pliocene in both the ,thomomyini and ,geomyini1 is the loss of enamel from the lateral surfaces of the cheek teeth1 and1 in the ,geomyini only1 the eventual loss of the anterior plate in the lower teeth and the posterior plate in the upper teeth4 ,both features were evolved more than an epoch earlier in the specialized entoptychid genus ,entoptychus of the lower ,miocene4 ,in ,entoptychus1 only the posterior plate of the lower molars and the anterior plate of the upper molars remained in the final stages of attrition1 although a central enamel fossette1 a remnant of the re-entrant fold1 remained throughout life4 ,iteration is also expressed in the subfamily ,geomyinae by the development of grooving on the upper incisor and the formation of the basitemporal fossa4 ,a shallow but distinct basitemporal fossa occurs between the coronoid process and the third lower molar in the genus ,entoptychus and a sulcated upper incisor1 a single shallow groove usually near the median border of the tooth1 is found in the genus ,gregorymys of the subfamily ,entoptychinae4 ,both features are regarded as advanced specializations in the tribe ,geomyini1 even though each was evolved in the entoptychines of the ,lower ,miocene4 ,the postcranial skeleton of living genera of pocket gophers1 as befits animals that spend most of their life within underground burrows1 are highly specialized for a fossorial life4 ,elements of the postcranial skeleton recovered from ,lower ,miocene deposits indicate that the entoptychines were only semi-fossorial 7see ,cope1 #ahhd3heg2 ,wood1 #aicf3d-e2 ,wilson1 #aidi3aag-aah74 ,one of the basic trends of the entoptychines was towards greater fossorial adaptation2 the skeleton of ,entoptychus shows a greater degree of fossorial adaptation than earlier genera of the subfamily4 ,there is no reason to suppose that the geomyine genus ,dikkomys1 which lived at the same times as the entoptychines1 had acquired any more advanced fossorial adaptations than had the entoptychines4 ,the most pronounced fossorial adaptations seem to have evolved only in the ancestral lineage of the modern geomyines1 probably in the latter part of the ,miocene and in the early ,pliocene1 before the modern ,thomomyini and ,geomyini diverged4 ,extreme fossorial adaptations in herbivorous rodents1 such as those characteristic of the modern pocket gophers and their immediate ancestors1 are thought to have evolved only in response to pronounced arid conditions4 ,the ,entoptychinae and evidently the early geomyines lived in environments that were either tropical or temperate1 and under conditions more mesic than ,i would consider necessary to bring about selection pressure resulting in fossorial specializations4 ,in late ,oligocene and early ,miocene1 according to ,axelroad 7#aieh3dcc-eji71 arid conditions did not exist in the ,united ,states1 and the only xerophytic environments in ,north ,america occurred on the ,central ,plateau of ,mxico4 ,moreover 7,axelroad1 loc4 cit471 arid conditions did not develop in the western ,united ,states until the early ,pliocene4 ,geomyids evidently became extinct in this region at the close of the ,middle ,miocene1 and none appear in fossil deposits in the western ,united ,states until the latest ,lower ,pliocene 7,clarendonian74 ,the reappearance of geomyids1 ,pliosaccomys1 in the western ,united ,states coincides with a trend toward aridity and the northward movement of the ,madro-tertiary geoflora into the ,great ,basin and ,great ,plains from its place of origin on the ,central ,plateau of ,mxico 7,axelroad1 loc4 cit474 ,later1 in the middle and later ,pliocene1 the ,madro-tertiary geoflora gave rise to the modern xerophytic plants that now characterize the desert vegetation of ,north ,america4 ,the ,madro-tertiary climax does not appear as a major flora until the ,miocene1 but probably originated earlier4 ,according to ,axelroad 7loc4 cit471 this xerophytic flora evolved from elements of the ,neotropical-tertiary geoflora that became adapted to arid conditions that developed in the rain shadow of the high mountains flanking the ,central ,plateau of ,mxico4 ,originally1 the ,madro-tertiary flora consisted of small trees1 shrubs1 and grasses4 ,although some elements of this flora moved northward in the late ,miocene1 the major part of it remained in ,mxico until the early ,pliocene4 ,in the western ,united ,states1 mountain formation increased in intensity in the ,pliocene and continued on into the early ,pleistocene4 ,as the mountains became more elevated1 especially the ,sierra ,nevada and ,cascade ranges1 they blocked the prevailing winds from the ,pacific ,ocean and extensive aridity developed on their leeward side4 ,as xeric conditions became widespread1 the ,madro-tertiary flora successfully occupied the drier regions of southern ,california1 the ,great ,basin1 and the western parts of the ,great ,plains4 ,while the ,entoptychinae probably evolved in response to the ,arcto-tertiary flora1 the late ,tertiary geomyines probably evolved in response to the ,madro-tertiary geoflora on the ,central ,plateau of ,mxico4 ,some of these early geomyines1 especially ancestors of the modern lineages1 probably were pushed southward by competition with the more specialized entoptychines4 ,most geomyines were pushed out of the northern area of distribution1 except for ,dikkomys that survived in association with the entoptychids throughout the early and middle ,miocene4 ,during this time1 and probably continuing on into the late ,miocene1 the geomyines occurring to the south in ,mxico became adapted to the arid environments of the ,madro-tertiary geoflora4 ,of course1 information is lacking about climates in several parts of the late ,miocene and early ,pliocene4 ,when such information becomes available it conceivably could modify the hypothesis outlined immediately above4 ,the principal trend of evolution in these semi-fossorial rodents was toward more complete fossorial adaptation1 and the pronounced fossorial features characteristic of the modern pocket gophers were perfected4 ,this trend continued in response to the intense selection pressures in this arid environment4 ,the principal structural characters effected were in the postcranial anatomy1 especially in the skeletal and muscular systems4 ,consequently1 it is not surprising that in skull and dentition1 ,pliosaccomys differs but little from ,dikkomys4 ,therefore1 most of the basic structural specializations so far developed for subterranean existence probably had evolved by the time geomyines moved back north in the early ,pliocene4 ,both modern lineages1 the tribes ,thomomyini and ,geomyini1 have essentially the same fossorial features1 and it seems unlikely that these features were acquired independently in the relatively short period of time available to them after their divergence2 probably they were inherited from a common ancestor4 ,these probabilities indicate that the evolution of the fossorial specialization was in the later phyletic development of the tribe ,dikkomyini4 ,plio-,pleistocene radiation of ,geomyini ,unlike the lineage of the ,thomomyini that remained essentially rectilinear through out its history1 the ,geomyini in the late ,pliocene and the early ,pleistocene underwent adaptive radiation in a degree comparable to the earlier radiation of the ,entoptychinae1 and all of the later history of the tribe is dominated by the radiation--the resulting structural diversity4 ,at least four lineages were produced by the ,plio-,pleistocene radiation 7see ,fig4 #f72 each originated at essentially the same time 7late ,pliocene7 presumably from the same ancestral stock4 ,each of these lineages within the ,geomyini has given rise to one of the four modern genera3 ,zygogeomys1 ,geomys1 ,orthogeomys1 and ,pappogeomys4 ,illustration3 ,,fig4 #f4 ,plio-,pleistocene radiation of the ,tribe ,geomyini4 ,morphotype ,the immediate1 unknown1 ancestor probably lived on the ,central ,plateau of ,mxico4 ,after the radiation began the ancestors of ,geomys and ,zygogeomys extended their ranges northward4 ,features of the hypothetical morphotype1 that would permit derivation of the modern genera would include the following3 7#a7 ,skull generalized1 neither excessively long and narrow or short and broad2 7#b7 skull smoothly rounded1 without pronounced angularity1 rugosity or cresting 7sagittal crest probably lacking1 even in old individuals72 7#c7 zygomata slender1 without lateral platelike expansions2 7#d7 rostrum moderately broad2 7#e7 upper incisors bisulcate1 two grooves in pattern found in ,pliogeomys1 ,zygogeomys and ,geomys2 7#f7 lateral re-entrant angles of premolars obtuse2 7#g7 p#d having four enamel plates 7one on anterior wall1 one on posterior wall1 and two lateral plates7 and lower molars having one enamel plate on the posterior wall of tooth 7anterior plate is lacking72 7#h7 ,p#d having four enamel plates1 in same pattern as described for p#d1 ,m#a having two enamel plates 7one anterior and one posterior71 ,m#b same as ,m#a1 ,m#c having three plates 7one anterior1 two lateral on sides of posterior loph1 none posterior72 7#i7 ,m#c subtriangular in cross-section1 distinctly bicolumnar1 two columns marked by shallow re-entrant folds and connected by broad isthmus2 7#aj7 masseteric ridge large1 forming high crest bordering masseteric fossa2 7#aa7 basitemporal fossa shallow2 7#ab7 angular process of mandible short1 its lateral projection barely exceeding that of zygomatic arch4 ,specializations in ,genera ,in relation to the primitive morphotype1 increase in size1 simplification of dentition1 and changes in shape of skull are regarded as specializations4 ,considerable parallelism between the four lineages is seen4 ,but each lineage is distinguished by a combination of specialized features1 and three by a few unique specializations4 ,among trends resulting in simplification of the dentition1 reduction of enamel on the posterior wall of the upper cheek teeth has occurred in various degrees in all lineages of the ,geomyini even to loss of all enamel on the posterior wall of the premolars and molars in two genera4 ,loss of some enamel is more common on ,p#d than on ,m#a-b1 and has occurred in all genera 7see ,figs4 #g and #i47 ,in evolutionary sequence loss of enamel from ,m#a and ,m#b usually occurs after1 but never preceding1 the reduction of enamel on ,p#d4 ,loss of enamel plates from the posterior face of ,m#a and ,m#b is associated with the evolution of an efficient anterotransverse shearing action of the teeth4 ,on the anterior wall of those teeth no reduction of the cutting blade has been observed2 a complete anterior plate is retained in all living ,geomyini4 ,presence of both the posterior and anterior plates decreases the efficiency of transverse shearing1 by providing two upper plates 7anterior plate of one tooth and posterior plate of the preceding tooth7 over which the lower cutting blade simultaneously must pass with each movement4 ,the advantages of shearing over the more common mechanics of planing are largely lost unless the posterior plates are eliminated4 ,also1 none of the living ,geomyini have retained a definitive posterior enamel plate on ,m#c1 the last upper molar2 but two well-developed lateral plates1 that extend almost all of the way back to the posterior apex of ,m#c1 have been retained1 and1 together function as a posterior plate4 ,loss of either or both of the lateral plates of ,m#c is rare1 and occurs only in old individuals4 ,their loss in the final stages of wear may represent the beginning of a new trend in those species where it occurs 7the castanops-group of the subgenus ,cratogeomys74 ,in any case1 reduction of enamel takes place by transverse shortening of the plate through the complete loss of enamel on one end1 the diminution beginning first on the labial end and proceeding by progressive atrophy to the lingual end of the plate4 ,evidently1 when enamel has been eliminated from the labial end of a plate1 the rate of loss decreases markedly1 and the last stages of evolution1 terminating in complete loss of an enamel plate1 occurs more slowly4 ,evolution may be arrested before complete loss has occurred1 and that part of the enamel that remains forms a short1 vestigial plate restricted to the lingual one-fourth or one-third of the wall4 ,the enamel pattern of the lower dentition is the same in all of the diverging lineages1 with no evidence of additional loss of enamel from that which had already occurred in their common ancestor 7see ,figs4 #g and #i74 ,reduction and loss of enamel plates began and was terminated in the lower dentition before reduction began in the upper dentition4 ,other dental specializations have occurred in the shape of the third upper molar and in the pattern of grooving in the upper incisor4 ,unlike ,m#c of the ,thomomyini1 that of the ,geomyini differs in shape from ,m#b1 and its enamel investment differs from that of ,m#b4 ,primitively1 ,m#c was probably subtriangular in cross-section1 and the posterior loph evidently projected posteriorly as a short1 rudimentary heel that formed the apex of the triangle4 ,other shapes of ,m#c are considered to be specializations that have been derived from the primitive form4 ,in addition to the primitive subtriangular pattern1 the ,m#c of living ,geomyini may be suborbicular1 quadriform1 elongate1 or obcordate in shape4 ,usually each lineage is characterized by only one pattern1 but in one genus 7,pappogeomys7 all patterns occur4 ,of the different forms1 the elongate and obcordate seem to be the most highly specialized deviations from the triangular-shaped tooth4 ,the bicolumnar pattern is accentuated in the elongate type 7,fig4 #g;,d1 ,f1 ,h7 by deep lateral re-entrant folds1 on both the lingual and labial sides1 and by the elongation of the posterior loph into a pronounced heel4 ,teeth having this pattern have been illustrated by ,merriam 7#ahie3gf-hb7 in ,figures #bg 7#f and #g71 #bh 7c and d71 #cd 7#g through #ae71 and #ce 7#h74 ,illustration3 ,,fig4 #g4 ,molariform dentitions of the ,tribe ,geomyini4 ,drawings illustrating enamel patterns characteristic of ,pliogeomys1 ,zygogeomys1 and the subgenera of ,orthogeomys 7,orthogeomys1 ,heterogeomys and ,macrogeomys74 #e4 ,a4 ,pliogeomys buisi1 ,no4 #biaeg 7,,ummp71 holotype1 ,buis ,ranch 7,upper ,middle ,pliocene71 ,beaver ,co41 ,oklahoma4 ,right lower1 p#d-m#b 7m#c unknown74 ,b and ,c4 ,zygogeomys trichopus trichopus1 adult female1 ,no4 #eaiga 7,,fmnh71 ,mt4 ,tanctaro1 #aj1ejj ft41 ,michoacn4 ,left upper 7,b71 ,p#d-,m#c2 right lower 7,c71 p#d-m#c4 ,d and ,e4 ,subgenus ,orthogeomys4 ,orthogeomys grandis guerrerensis1 adult female1 ,no4 #cihjg 7,,ku71 #a_/b mi4 ,e ,la ,mira1 #cjj ft41 ,michoacn4 ,left upper 7,d71 ,p#d-,m#c2 right lower 7,e71 p#d-m#c4 ,f and ,g4 ,subgenus ,heterogeomys4 ,orthogeomys hispidus hispidus1 adult female1 ,no4 #bcige 7,,ku71 #d km4 ,w ,tlapacoyan1 #gjj ft41 ,veracruz4 ,left upper 7,f71 ,p#d-,m#c2 right lower 7,g71 p#d-m#c4 ,h and ,i4 ,subgenus ,macrogeomys4 ,orthogeomys heterodus cartagoensis1 adult female1 ,no4 #fjffd 7,,ku71 ,rancho ,redando1 ,volcn ,lroz1 ,prov4 ,san ,jos1 ,costa ,rica4 ,left upper 7,h71 ,p#d-,m#c2 right lower 7,i71 p#d-m#c4 ,the subcordate form is characterized by pronounced anteroposterior compression1 and retention of a distinct labial re-entrant fold4 ,the posterior loph apparently has been rotated in such a way that what was previously its posterior border now lies on the outer margin of the tooth2 therefore1 the axis of the posterior loph is strongly oblique in relation to the anteroposterior bearing of the maxillary tooth-row1 and the median enamel plate also has been rotated and so lies transversely across the posterior wall of the tooth4 ,owing to the rotation of the posterior loph1 the apex of the obcordate tooth is at its lingual side4 ,the subcordate type is illustrated by ,merriam 7loc4 cit47 in ,figures #bg 7#c and #d71 #bh 7a and b71 #cd 7#c and #d71 and #ce 7#e1 #f1 and #g74 ,the suborbicular and quadriform types are less specialized than the two described above4 ,both are characterized by reduction1 often obliteration1 of the bicolumnar pattern of the subtriangular ancestral form1 especially marked by the decrease in depth of the lateral re-entrant folds and the decrease in length of the posterior projection of the posterior loph4 ,with these changes1 the tooth becomes essentially monocolumnar1 its occlusal surface oval in outline in one and squarish in shape in the other4 ,occlusal views of the suborbicular form are presented by ,merriam 7loc4 cit47 in ,figure #cc 7#a1 #e1 #f1 #g1 #aa1 and #ab7 and the quadriform tooth is depicted in ,figure #bi4 ,grooved upper incisors are characteristic of the living ,geomyini1 but variation occurs in the number of grooves1 and1 if only one groove is present1 its position on the anterior face of the tooth varies4 ,except for the previously mentioned 7p4 #dhj7 abnormal tooth having three grooves1 incisors with no more than two grooves are found in these pocket gophers1 and this number of grooves is taken to be primitive4 ,loss of one or the other of the two grooves of the bisulcate pattern1 therefore1 is regarded as specialization4 ,however1 complete loss of both grooves never occurs in the ,geomyini4 ,each of the four major lineages is characterized by one of the three patterns of grooving1 and the particular groove-pattern is remarkably stable in each group4 ,shape of skull varies from dolichocephalic to platycephalic4 ,the morphology of each has been described in foregoing accounts4 ,the dolichocephalic skull is highly specialized for planing1 a grinding action of the teeth2 whereas1 the platycephalic skull is highly specialized for shearing1 a slicing action of the teeth4 ,of course1 concomitant specializations of the dentition1 as described above1 are closely associated with both specialized trends in the skull4 ,most kinds of living ,geomyini have generalized skulls that show no tendency toward either of the specialized conditions4 ,increase in size of body and skull is seen in most ,pleistocene lineages of the ,geomyini4 ,judging from the smallness of the skull in late ,pliocene species1 representing the base of three of these lineages1 the ancestral species of the living assemblage were no larger than the living species of the subgenus ,pappogeomys or the smaller subspecies of ,geomys bursarius4 ,the recorded range of variation in condylobasal length is #cf4a to #de4e in ,pappogeomys bulleri1 including both adult males and females4 ,probably the skulls of the ancestral species were not significantly larger4 ,maximum dimensions of males in living species are #gd4e 7subgenus ,cratogeomys7 and #ge4j 7subgenus ,orthogeomys74 ,these are more than twice the minima observed in ,pappogeomys bulleri4 ,zygogeomys ,this is the least specialized and most primitive of the four lineages1 has a generalized type of skull1 two grooves on the anterior face of each upper incisor1 an enamel plate on the posterior wall of ,p#d1 open or divergent lateral re-entrant angles on the premolars1 and a bicolumnar and elongated ,m#c4 ,all of these features are primitive and essentially as in the ancestral morphotype4 ,no other modern genus retains so much of the primitive structure4 ,phyletic trends in ,zygogeomys are not well documented in the fossil record2 and only a few fossils are known and they are fragmentary as discussed before4 ,the genus is represented in the late ,pliocene 7,z4 minor71 middle ,pleistocene 7,z4 persimilis71 and ,recent 7,z4 trichopus74 ,the living species is a relict population in the mountains of ,central ,mxico4 ,judging from the known material1 the phyletic trends in the genus have been increase in size1 reduction of enamel on the posterior face of ,p#d 7occurring only in the living species7 where a short enamel plate is retained on the lingual side of the tooth 7see ,fig4 #g;,b71 loss of the outer fourth of the enamel blade on the posterior wall of ,m#a and ,m#b 7also occurring only in the living species71 development of a more pronounced heel on the ,m#c by progressive elongation of the posterior loph1 reduction in size of the jugal and its displacement ventrally1 which allows the maxillary and squamosal bones to meet along the dorsal border of the zygomatic arch4 ,the last specialization is seen in at least one taxon of ,orthogeomys 7,orthogeomys cherriei costaricensis74 ,in my opinion1 too much weight has been given to this feature in past classifications4 ,reduction of enamel in the upper dentition evidently occurred in the late ,pleistocene1 since the posterior plates on the upper cheek teeth were complete in specimens from the middle ,pleistocene 7,z4 persimilis74 ,geomys ,geomys1 slightly more specialized than ,zygogeomys1 must also be regarded as one of the most primitive of the living genera4 ,primitive features that have been retained are the generalized type of skull1 the bisulcate pattern of grooves on the upper incisor1 and the retention of enamel plates on both the anterior and posterior walls of ,m#a and ,m#b 7see ,fig4 #i;,a74 ,all of these primitive features are shared with ,zygogeomys4 ,in addition1 three other trends1 or specializations1 in evolution characterize the phyletic development of ,geomys4 ,one major trend is toward loss of the enamel plate from the posterior wall of ,p#d4 ,no trace of enamel remains on the posterior wall of this tooth in late ,pleistocene or ,recent species of ,geomys1 and at least one of the earlier species 7quinni7 was also characterized by loss of this enamel plate4 ,secondly1 ,m#c retains only a vestige of the primitive bicolumnar pattern after the initial stages of wear4 ,in most ,recent specimens1 especially of the species ,g4 bursarius1 the lateral re-entrant fold and the heel of ,m#c are small1 and the re-entrant inflection is hardly evident4 ,the lateral fold is more frequently well-developed in ,irvingtonian species than in living species 7,white and ,downs1 #aifa3ac71 illustrating progressive loss of the bicolumnar pattern in ,pleistocene evolution4 ,a third trend involves the modification of the lateral folds of the premolars4 ,primitively the angles of these folds are broadly open or divergently ,v-shaped1 and some of the earliest species of ,geomys1 for example ,g4 quinni1 have retained this feature throughout life4 ,nevertheless1 the main trend is toward progressive compression of the folds resulting in their walls being more nearly perpendicular1 and parallel1 to the long axis of the tooth4 ,obtuse re-entrant angles persist in premolars of young individuals of ,irvingtonian species1 but the adults are characterized by well-compressed folds1 as in ,recent species4 ,remains of ,geomys are abundant1 especially from ,pleistocene deposits of the ,great ,plains1 but in most instances specific assignment is difficult or impossible since only isolated teeth or fragments of skulls have been preserved4 ,estimates of phyletic relationships of the known species of ,geomys are depicted in ,figure #h2 those estimates are useful in discussing the phyletic development of the genus4 ,one of the earliest known species1 ,geomys quinni1 ranges from ,upper ,pliocene to the later stages of the ,lower ,pleistocene 7,aftonian interglacial deposits74 ,the dentition of ,g4 quinni is essentially the same as in the living species except that open lateral re-entrant angles are retained in the premolars4 ,geomys paenebursarius1 also of the early ,pleistocene1 is a smaller species and seems to be more directly in the line of evolution of the modern species4 ,as yet unnamed smaller species of ,geomys from the ,rexroad fauna 7late ,pliocene7 and ,saunders fauna 7latest ,aftonian7 may also be on the main line of evolution4 ,surprisingly1 ,geomys tobinensis and ,geomys garbanii of later ,irvingtonian provincial age are less specialized than either ,geomys quinni or ,geomys paenebursarius4 ,it is likely that ,g4 tobinensis and the unnamed species from the ,dixon are closer to the main line of descent than ,g4 paenebursarius suggesting that the direct ancestral lineage of the living species of ,geomys was more conservative and less specialized than ,geomys paenebursarius of the ,lower ,pleistocene4 ,geomys quinni and ,g4 paenebursarius seem to have acquired specialized dental features in the early ,pleistocene4 ,geomys quinni was successful on the ,great ,plains1 and persisted into the late ,blancan4 ,the main line may be represented in the early ,pleistocene by ,geomys paenebursarius from the ,hancock formation of the ,texas ,trans-,pecos4 ,the structure of ,g4 paenebursarius indicates that it is in or close to the main line of descent1 and probably evolved from one of the more primitive late ,pliocene species of ,geomys from the ,rexroad fauna4 ,illustration3 ,,fig4 #h4 ,tentative arrangement of species of the genus ,geomys1 depicting phylogenetic trends and probable relationships within the genus4 ,isolated teeth1 to which the name ,geomys bisulcatus probably applies1 from ,illinoian deposits on the ,great ,plains1 show that the dentition characteristic of the living ,geomys had been developed by that time4 ,actually1 the ,illinoian material is too fragmentary to show clearly its taxonomic or phyletic affinities with the species of the later ,pleistocene4 ,even so1 the two main stocks of living ,geomys1 ,g4 bursarius and ,g4 pinetis1 had certainly been differentiated by ,sangamon time4 ,the other living species evidently evolved from one or the other of these two stocks in a period of isolation from the main population1 probably in either the ,wisconsin or post-,wisconsin4 ,for example1 ,geomys arenarius clearly differentiated from populations of ,geomys bursarius that were isolated by the eastward retreat of the main population from the southwestern ,united ,states as that region became more arid in the post-,wisconsin4 ,in review1 it seems that the ,recent species1 represented basically by bursarius and pinetis1 evolved from ,illinoian species 7,geomys bisulcatus871 which descended in turn from the more primitive species of the early ,pleistocene1 possibly ,geomys paenebursarius or possibly from descendants of the ,saunders species4 ,actually the ,saunders species may prove to be ,geomys paenebursarius4 ,at any rate1 three trends that took place during the ,pleistocene stage of evolution1 in the direction of the modern species1 were an increase in size1 progressive loss of the posterior enamel plate on ,p#d1 and a decrease in the vertical depth of the enamel cap as a result of which the dentine is reached in the initial phases of attrition on the tooth of a juvenile4 ,geomys garbanii1 occurring at the periphery of the range of the genus1 is regarded as a sterile offshoot of the primitive tobinensis-line of evolution4 ,orthogeomys ,this is one of the more specialized genera of the ,geomyini4 ,save for one record in the late ,pleistocene 7,orthogeomys onerosus71 there is no fossil history of the genus upon which to reconstruct its phylogeny2 therefore1 its phyletic development must be estimated by comparing it and the primitive morphotype of the tribe4 ,results of that comparison suggest that ,orthogeomys has closer affinities with ,zygogeomys than with any of the other genera1 and that ,orthogeomys may have originated in an early dichotomy of primitive ,zygogeomys stock instead of descending from the ancestral stock of the tribe4 ,except for the unisulcate incisors and the longer posterior loph on the third upper molars1 the teeth of the two genera do not differ significantly4 ,as in ,zygogeomys1 the enamel blade on the posterior wall of ,p#d has been reduced to a short plate restricted to the lingual third of the tooth 7see ,fig4 #g;,f and ,h74 ,in ,orthogeomys1 the trend in reduction of enamel is carried to its extreme only in the subgenus ,orthogeomys1 where this plate has been completely lost in most taxa 7see ,fig4 #g;,d74 ,the most significant trends in ,orthogeomys1 and the principal basis for recognizing the genus1 are the dolichocephalic specializations of the skull1 as described elsewhere1 and the adaptive traits that have equipped the genus for living in tropical environments4 ,the dolichocephalic features are more sharply defined in the subgenera ,orthogeomys and ,macrogeomys1 and are less developed in the subgenus ,heterogeomys4 ,aside from the general dolichocephalic specializations1 trends in ,orthogeomys include3 ,increase in size2 loss of the median one of the two grooves on the anterior face of the upper incisor in the ancestral stock2 increase in the anteroposterior length of each of the cheek teeth1 as well as the aforementioned elongation of the posterior loph of ,m#c2 compression of the lateral angles of the premolars2 and the remarkable increase in the size of the rostrum4 ,pappogeomys ,the genus ,pappogeomys1 as it is conceived of in this study1 is comprised of two subgenera2 one1 ,pappogeomys1 is generalized and primitive1 and the other1 ,cratogeomys1 is specialized1 and includes the most highly specialized of the modern pocket gophers4 ,the subgenus ,pappogeomys is regarded as the ancestral lineage1 and the subgenus ,cratogeomys is regarded as an early offshoot1 probably in the early ,pleistocene1 that became progressively more specialized in the course of its subsequent evolution4 ,in the same period of time1 the subgenus ,pappogeomys changed little4 ,it is known only from late ,pliocene fragments and from the living species4 ,the ancestral morphotype is preserved in ,pappogeomys4 ,primitive characters are3 7#a7 ,small size2 7#b7 skull generalized and smoothly rounded2 7#c7 temporal ridges separate 7not uniting into a sagittal crest72 7#d7 enamel plates retained on both anterior and posterior walls of ,m#a and ,m#b2 7#e7 ,m#c bilophate1 its posterior loph short4 ,basic specializations are few and include loss of the inner groove from the anterior face of the upper incisor2 anteroposterior compression of the lateral re-entrant folds of the premolars2 and loss of enamel from the posterior wall of ,p#d4 ,all three features have been perpetuated in the advanced subgenus ,cratogeomys1 suggesting that they were already developed in the early evolution of the subgenus ,pappogeomys before ,cratogeomys diverged4 ,agreement with ,geomys is demonstrated by the lack of enamel on the posterior wall of ,p#d 7see ,fig4 #i7 and by retention of the posterior enamel plate on ,m#a and ,m#b4 ,in ,pappogeomys 7,pappogeomys7 alcorni the enamel from the posterior face of ,m#a has been lost from all but the lingual fourth or so of the posterior wall 7,fig4 #i;,e74 ,reduction of enamel in ,m#a provides an example of parallelism with the more advanced subgenus ,cratogeomys1 discussed below4 ,there is no record as yet of the early evolution of the subgenus ,cratogeomys4 ,the features that characterize the subgenus were already well developed in the first known fossils which are from ,wisconsin deposits of the late ,pleistocene4 ,cratogeomys is not a homogenous assemblage2 instead it is composed of two groups of living species1 the generalized castanops group and the specialized gymnurus group4 ,the castanops group may be survivors of the ancestral lineage that diverged in two different stages in the phyletic development of the main line4 ,even so1 the castanops group has acquired its peculiar specializations4 ,indeed1 ,p4 merriami of the castanops group differs from the hypothetical stem more than does ,p4 castanops4 ,judging from the structure of the living species of the subgenus ,cratogeomys and from the primitive subgenus ,pappogeomys1 the subgenus ,cratogeomys featured five major trends3 7#a7 ,increase in size2 7#b7 formation of sagittal crest by union of the temporal impressions2 7#c7 increase in rugosity and angularity of the skull2 7#d7 progressive development of platycephalic specializations1 including the elongation of the angular process of the mandible2 7#e7 complete loss of enamel plates from the posterior wall of ,m#a and ,m#b4 ,each trend is thought to be adaptive4 ,illustration3 ,,fig4 #i4 ,molariform dentitions of the ,tribe ,geomyini4 ,drawings illustrating enamel patterns characteristic of ,geomys and ,pappogeomys 7including the subgenera ,pappogeomys and ,cratogeomys74 #e4 ,a and ,b4 ,geomys bursarius bursarius1 adult female1 ,no4 #dfbge 7,,ku71 ,elk ,river1 ,sherborne ,co41 ,minnesota4 ,left upper 7,a71 ,p#d-,m#c2 right lower 7,b71 p#d-m#c4 ,c and ,d4 ,subgenus ,pappogeomys4 ,pappogeomys bulleri albinasus1 adult female1 ,no4 #cajjb 7,,ku71 ,w side ,la ,venta1 #ac mi4 ,w and #d mi4 ,n ,guadalajara1 ,jalisco4 ,left upper 7,c71 ,p#d-,m#c2 right lower 7,d71 p#d-m#c4 ,e and ,f4 ,subgenus ,pappogeomys4 ,pappogeomys alcorni1 adult female1 ,no4 #cajea 7,,ku71 holotype1 #d mi4 ,w ,mazamitla1 #ffjj ft41 ,jalisco4 ,left upper 7,e71 ,p#d-,m#c2 right lower 7,f71 p#d-m#c4 ,g and ,h4 ,subgenus ,cratogeomys4 ,pappogeomys gymnurus tellus1 adult female1 ,no4 #cajea 7,,ku71 #a mi4 ,,ne ,tala1 #ddjj ft41 ,jalisco4 ,left upper 7,g71 ,p#d-,m#c2 right lower 7,h71 p#d-m#c4 ,loss of enamel is a trend common to all living genera of the tribe ,geomyini1 but the greatest loss has occurred in ,cratogeomys4 ,it has lost the plates on the posterior walls of ,m#a and ,m#b 7,fig4 #i;,g74 ,if the lateral plates of ,m#c are considered as one functional plate and the lateral plates on either side of ,p#d together as two transverse plates1 then1 the transverse cutting blades in ,cratogeomys number seven in the upper and seven in the lower cheek teeth compared with #aj in the upper and seven in the lower in the primitive morphotype4 ,indeed1 in some species of the subgenus1 one or both of the lateral plates on ,m#c is also lost1 usually in old age1 resulting in even greater reduction of enamel4 ,loss of enamel from the posterior walls of the upper molars may be associated with changes in the mechanics of mastication from anteroposterior planing to anterotransverse shearing1 as discussed elsewhere4 ,merriam 7#ahie3ie-if7 argues convincingly that the posterior cutting blades of the upper molars would hinder efficient shearing action of the teeth2 hence1 selection would favor their reduction and eventual loss4 ,changes in the shape of the skull also seem to be correlated with the shift from a planing to a shearing type of mastication4 ,more efficient shearing action1 which depends upon lateral movement of the jaw1 can be developed if the functional muscles insert farther laterally than is possible in the generalized type of skull4 ,therefore1 platycephalic specializations involved lateral expansion of the braincase and mandible4 ,pronounced lateral expansion has been developed only in the gymnurus group of species1 suggesting that the dental specializations evolved earlier in the evolution of the subgenus than did the platycephalic specializations of the skull1 and that the castanops group separated from the gymnurus group before the common ancestor had developed the more extreme trends in platycephaly4 ,it is interesting to note that the subtriangular ,m#c 7,fig4 #i;,g7 postulated for the ancestral morphotype and that characterizes the subgenus ,pappogeomys is retained also in the gymnurus group4 ,,literature ,,cited ,,alston1 ,e4 ,r4 #ahgf4 ,on the classification of the order ,glires4 ,proc4 ,zool4 ,soc4 ,london1 #ahgf3fa-ih1 #a pl41 ,june4 ,,alvarez1 ,t4 #aifd4 ,nota sobre restos oseos de mamiferos del ,reciente1 encontrados cerca de ,tepeapulco1 ,hidalgo1 ,mexico4 ,publ4 ,inst4 ,nac4 ,antro1 e ,hist41 #ae3a-ae4 #aife4 ,catlago ,paleomastozoolgico ,mexicano4 ,publ4 ,inst4 ,nac4 ,antro1 e ,hist41 #ag3a-gj4 ,,axlerod1 ,d4 ,i4 #aiej4 ,studies in late ,tertiary paleobotany4 ,carnegie ,inst4 ,washington ,publ41 #eij3a-cbb4 #aieh4 ,evolution of the ,madro-tertiary geoflora4 ,bot4 ,rev41 #bd3dcc-eji4 ,,bader1 ,r4 ,s41 and ,,techter1 ,d4 #aiei4 ,a list and bibliography of the fossil mammals of ,illinois4 ,nat4 ,hist4 ,misc41 ,chicago ,acad4 ,sci41 #agb3a-h1 ,october #cj4 ,,baird1 ,s4 ,f4 #aheh4 ,mammals4 ,part ,i4 ,general report upon the zoology of the several ,pacific railroad routes4 ,repts41 explorations and surveys for a railroad route from the ,mississippi ,river to the ,pacific ,ocean4 ,washington1 ,d4 ,c41 vol4 #h1 pp4 xlviii #geg1 #ce figs41 #dc pls41 ,july #ad4 ,,barbour1 ,h41 and ,,schultz1 ,c4 ,b4 #aicg4 ,an early ,pleistocene fauna from ,nebraska4 ,amer4 ,mus4 ,nat4 ,hist4 ,novit41 #idb3a-aj1 ,september #aj4 ,,berry1 ,e4 ,w4 #aicg4 ,tertiary floras of ,north ,america4 ,bot4 ,rev41 #c3ca-df4 ,,black1 ,c4 ,c4 #aifa4 ,rodents and lagomorphs from the ,miocene ,fort ,logan and ,deep ,river ,formations of ,montana4 ,postilla1 ,yale ,peabody ,museum1 #dh3a-bj1 #f figs41 ,january #af4 ,,brandt1 ,j4 ,f4 #ahee4 ,beitrge zur mhern ,kenntiss der ,sugethiere ,russlands4 ,acad4 ,imp4 des ,sciences ,st4 ,petersburg1 #g3gi-ccf1 #aa pls4 ,,brown1 ,b4 #aijh4 ,the ,conard fissure1 a ,pleistocene bone deposit in northern ,arkansas with description of two genera #bj new species of mammals4 ,mem4 ,amer4 ,mus4 ,nat4 ,hist41 #i3aeg-bjh1 #b pls41 #c figs4 #aiab4 ,brachyostracon1 a new genus of glyptodont from ,mexico4 ,bull4 ,amer4 ,mus4 ,nat4 ,hist41 #ca3afg-agg1 ,august #b4 ,,chaney1 ,r4 ,w4 #aidg4 ,tertiary centers and migration routes4 ,ecol4 ,monog41 #ag3aci-adh4 ,,cook1 ,h4 ,j41 and ,,cook1 ,m4 ,c4 #aicc4 ,faunal lists of the ,tertiary ,vertebrata of ,nebraska and adjacent areas4 ,nebraska ,geol4 ,surv41 ,paper ,no4 #e3di4 ,,cope1 ,e4 ,d4 #ahgh4 ,description of new extinct ,vertebrata from the upper ,tertiary and ,dakota formations4 ,bull4 ,u4 ,s4 ,geol4 and ,geog4 ,surv41 #d3cgi-cif4 #ahhd4 ,the ,white ,river and ,john ,day faunae1 pp4 #gei-ajjb1 pl4 #fd1 figs4 #a-i4 ,in ,the ,vertebrata of the ,tertiary formations of the west4 ,book ,i4 ,part second4 ,rept4 ,u4 ,s4 ,geol4 ,surv4 ,terr4 7,f4 ,v4 ,hayden71 vol4 #c4 #ahhi4 ,the vertebrate fauna of the ,equus beds4 ,amer4 ,nat41 #bc3afj-afe4 ,,coues1 ,e4 #ahgg4 ,monographs of ,north ,american ,rodentia4 ,no4 #h1 ,saccomyinae1 pp4 #dhc-edb1 and ,no4 #aj1 ,geomyinae1 pp4 #fja-fbi1 pl4 #g1 ,august4 ,,dalquest1 ,w4 ,w4 #aifb;a4 ,a record of the giant bison 7,bison latifrons7 from ,cooke ,county1 ,texas4 ,texas ,jour4 ,sci41 #ac3da-dd1 ,march4 #aifb;b4 ,the ,good ,creek ,formation of ,texas1 and its fauna4 ,jour4 ,paleont41 #cf3efh-ehb4 #aifd4 ,a new ,pleistocene local fauna from ,motley ,county1 ,texas4 ,trans4 ,kansas ,acad4 ,sci41 #fg3dii-eje1 #d figs41 ,december #aa4 #aife4 ,new ,pleistocene ,formation and local fauna from ,hardeman ,county1 ,texas4 ,jour4 ,paleont41 #ci3fc-gb1 #b figs41 ,january4 ,,dice1 ,l4 ,r4 #aibe4 ,rodents and lagomorphs of the ,rancho ,la ,brea ,deposits4 ,carnegie ,inst4 ,washington ,publ41 #cdi3aai-acj4 ,,davis1 ,w4 ,b4 #aicg4 ,variations in ,townsend pocket gophers4 ,jour4 ,mamm41 #ah3ade-aeh1 ,may #ab4 ,,ellerman1 ,j4 ,r4 #aidj4 ,the families and genera of living rodents4 ,vol4 ,i4 ,rodents other than ,muridae4 ,british ,museum 7,nat4 ,hist471 ,london1 pp4 xxvi #fhi1 #ahi figs41 ,june #h4 ,,elliott1 ,d4 ,g4 #aijc4 ,a list of mammals obtained by ,edmund ,heller from the coast region of northern ,california and ,oregon4 ,field ,columb4 ,mus4 ,publ41 #gf1 zool4 ser4 vol4 #c7aa73age-aig1 ,july #be4 ,,elftman1 ,h4 ,o4 #aica4 ,pleistocene mammals of ,fossil ,lake1 ,oregon1 ,amer4 ,mus4 ,novit41 #dha3a-ba1 #aj figs41 ,july #ad4 ,,franzen1 ,d4 ,s4 #aidg4 ,the pocket gopher1 ,geomys quinni ,mc,grew1 in the ,rexroad fauna1 ,blancan age1 of southwestern ,kansas4 ,trans4 ,kansas ,acad4 ,sci41 #ej3ee-ei4 ,,freudenberg1 ,w4 #aiba4 ,geologie von ,mexiko4 ,berlin1 pp4 viii #bcb4 ,,galbreath1 ,e4 ,c4 #ahdh4 ,an additional specimen of the rodent ,dikkomys from the ,miocene of ,nebraska4 ,trans4 ,kansas ,acad4 ,sci41 #ea3caf-cag4 ,,gazin1 ,c4 ,l4 #aice4 ,annotated list of ,pleistocene ,mammalia from ,american ,falls1 ,idaho1 ,jour4 ,washington ,acad4 ,sci41 #be3big-cjb4 #aidb4 ,the late ,cenozoic vertebrate fauna from the ,san ,pedro ,valley1 ,arizona4 ,proc4 ,u4 ,s4 ,nat4 ,mus41 #ib7caee73dge3eah1 #b pls41 #i figs4 ,,gervais1 ,p4 #ahdi4 ,rongeurs4 ,in ,dictionnaire universel d'historie naturelle1 ,dirig par ,m ,ch4 d',orbigny1 ,paris1 ,m4 ,m4 ,renard1 ,martinet et ,cie1 vol4 #aa3aih-bjd4 ,,gidley1 ,j4 ,w4 #aibb4 ,preliminary report on fossil vertebrates of the ,san ,pedro ,valley1 ,arizona1 with descriptions of new species of ,rodentia and ,lagomorpha4 ,u4 ,s4 ,geol4 ,surv4 ,prof4 ,papers1 #aca3aai-acj1 pls4 #cd and #ce4 ,,gidley1 ,j4 ,w41 and ,,gazin1 ,c4 ,l4 #aicc4 ,new ,mammalia in the ,pleistocene fauna from ,cumberland ,cave4 ,jour4 ,mamm41 #ad3cdc-ceg1 #i figs4 ,,gill1 ,t4 ,h4 #ahgb4 ,arrangement of the families of mammals with analytical tables4 ,smithsonian ,misc4 ,coll41 #aa1 art4 #a1 pp4 vi #ih4 ,,gilmore1 ,r4 ,m4 #aidg4 ,report on a collection of mammal bones from archeologic cave-sites in ,coahuila1 ,mexico4 ,jour4 ,mamm41 #ch3adg-afe1 ,june #a4 ,,gray1 ,j4 ,e4 #ahfh4 ,synopsis of the species ,saccomyinae or pouched mice in the collection of the ,british ,museum4 ,proc4 ,zool4 ,soc4 ,london1 #ahfh3aii-bjf1 ,may4 ,,green1 ,m4 #aief4 ,the lower ,pliocene ,ogallala-,wolf ,creek vertebrate fauna1 ,south ,dakota4 ,jour4 ,paleo41 #cj7a73adf-afi1 #ab figs41 ,january4 ,,gut1 ,h4 ,j41 and ,,ray1 ,c4 ,e4 #aifc4 ,the ,pleistocene vertebrate fauna of ,reddick1 ,florida4 ,quart4 ,jour4 ,florida ,acad4 ,sci41 #bf3cae-cbh4 ,,hall1 ,e4 ,r41 and ,,kelson1 ,k4 ,r4 #aiei4 ,the mammals of ,north ,america4 #b vols41 xxx #ajhc pp41 #eec figs41 #ejj maps1 ,march #ca4 ,,harris1 ,a4 ,h41 and ,,findley1 ,j4 ,s4 #aifd4 ,pleistocene--,recent fauna of the ,isleta ,caves1 ,bernalillo ,county1 ,new ,mexico4 ,amer4 ,jour4 ,sci41 #bfb3aad-abj1 ,january4 ,,hay1 ,o4 ,p4 #aibj4 ,description of some ,pleistocene vertebrates found in the ,united ,states4 ,proc4 ,u4 ,s4 ,nat4 ,mus41 #eg3hc-adf1 #h pls41 #d figs4 #aiba4 ,description of species of ,pleistocene vertebrate types of specimens of most of which are preserved in the ,u4 ,s4 ,national ,museum4 ,proc4 ,u4 ,s4 ,nat4 ,mus41 #ei3eii-fdb4 #aibc4 ,the ,pleistocene of ,north ,america and its vertebrated animals from the states east of the ,mississippi ,river and from the ,canadian provinces east of longitude #ie4 ,carnegie ,inst4 ,washington1 ,publ4 #cbb3 #a-dii1 ,february #bd4 #aibd4 ,the ,pleistocene of the middle region of ,north ,america and its vertebrated animals4 ,carnegie ,inst4 ,washington1 ,publ4 #cbb;,a3#a-cdf4 #aibg4 ,the ,pleistocene of the western region of ,north ,america and its vertebrate animals4 ,carnegie ,inst4 ,wash41 ,publ4 #cbb;,b1 pp4 v #cdf1 #ab pls41 #ba maps1 #aj text figs4 ,,hibbard1 ,c4 ,w4 #aich4 ,an ,upper ,pliocene fauna from ,meade ,county1 ,kansas4 ,trans4 ,kansas ,acad4 ,sci41 #dj3bci-bfe1 #e pls41 #b figs4 #aida;a4 ,the ,borchers fauna1 a new ,pleistocene interglacial fauna from ,meade ,county1 ,kansas4 ,bull4 ,state ,geol4 ,surv4 ,kansas1 #ch3aig-bbj1 #b pls41 ,july #ad4 #aida;b4 ,mammals of the ,rexroad ,fauna from the ,upper ,pliocene of southwestern ,kansas4 ,trans4 ,kansas ,acad4 ,sci41 #dd3bfe-cac1 #d pls4 #aidc4 ,the ,rezabek fauna1 a new ,pleistocene fauna from ,lincoln ,county1 ,kansas4 ,univ4 ,kansas ,sci4 ,bull41 #bi3bce-bdg1 ,october #ae4 #aidd4 ,stratigraphy and vertebrate paleontology of ,pleistocene deposits of southwestern ,kansas4 ,geol4 ,soc4 ,amer4 ,bull41 #ee3gjg-ged1 #c pls41 #bj figs4 #aiej4 ,mammals of the ,rexroad ,formation from ,fox ,canyon1 ,meade ,county1 ,kansas4 ,univ4 ,michigan ,paleo4 ,contrib41 #h7f73aac-aib1 #e pls41 #bc figs4 #aiea4 ,thomomys talpoides 7,richardson7 from a late ,pleistocene deposit in ,kansas4 ,jour4 ,mamm41 #cb3bbi-bcj4 #aieb4 ,vertebrate fossils from late ,cenozoic deposits of central ,kansas4 ,univ4 ,kans4 ,paleont4 ,contrib41 ,vertebrata1 #b3a-ad1 ,march #bj4 #aiec4 ,the ,saw ,rock ,canyon fauna and its stratigraphic significance4 ,papers ,michigan ,acad4 ,sci41 ,arts1 and ,letters1 #ch3chg-daa4 #aied4 ,a new ,pliocene vertebrate fauna from ,oklahoma4 ,papers ,michigan ,acad4 ,sci41 ,arts1 ,letters1 #ci3cci-cei4 #aiee;a4 ,pleistocene vertebrates from the upper ,bercerra 7,bercerra ,superior7 ,formation1 valley of ,tecquixquiac1 ,mexico1 with notes on other ,pleistocene forms4 ,contribution from ,mus4 ,paleo41 ,univ4 ,michigan1 #ab3dg-if1 #i pls41 #e figs41 ,february #ah4 #aiee;b4 ,the ,jinglebob interglacial 7,sangamon87 fauna from ,kansas and its climatic significance4 ,contrib4 ,mus4 ,paleo41 ,univ4 ,michigan1 #ab3 #agi-bbh1 #b pls41 #h figs41 ,september #a4 #aief4 ,vertebrate fossils from the ,meade ,formation of southwestern ,kansas4 ,papers ,michigan ,acad4 ,sci41 ,arts1 and ,letters1 #da3ade-bjj4 #aieh4 ,summary of ,north ,american ,pliestocene mammalian local faunas4 ,papers of ,michigan ,acad4 ,sci41 ,arts1 and ,letters1 #dc3a-cb4 #aifc4 ,a late ,illinoian fauna from southwestern ,kansas and its climatic significance4 ,papers ,michigan ,acad4 ,sci41 ,arts and ,letters1 #dh3ahg-bba1 #h figs4 ,,hibbard1 ,c4 ,w41 and ,,keenmon1 ,k4 ,a4 #aiej4 ,new evidence of the ,lower ,miocene age of the ,blacktail ,deer ,creek ,formation in ,montana4 ,contrib4 ,univ4 ,michigan ,mus4 ,paleo41 #h3aic-bjd1 #c figs41 #a map1 ,july #bh4 ,,hibbard1 ,c4 ,w41 and ,,mooser1 ,o4 #aifc4 ,a porcupine from the ,pleistocene of ,aguascalientes1 ,mexico4 ,contrib4 ,mus4 ,paleo4 ,univ4 ,michigan1 #ah3bde-bej1 ,november #bb4 ,,hibbard1 ,c4 ,w41 ,,ray1 ,d4 ,e41 ,,savage1 ,d4 ,e41 ,,taylor1 ,d4 ,w41 ,,guilday1 ,g4 ,e4 #aife4 ,quaternary mammals of ,north ,america4 ,in ,quaternary of the ,united ,states4 ,eds4 ,h4 ,e4 ,wright1 ,jr41 and ,d4 ,g4 ,frey4 ,princeton ,univ4 ,press1 ,princeton1 pp4 x #ibb4 ,,hibbard1 ,c4 ,w41 and ,,riggs1 ,e4 #aidi4 ,upper ,pliocene vertebrates from ,keef ,canyon1 ,meade ,county1 ,kansas4 ,geol4 ,soc4 ,amer4 ,bull41 #fj7e73hbi-hfj1 #aa figs41 #e pls4 ,,hibbard1 ,c4 ,w41 and ,,taylor1 ,d4 ,w4 #aifj4 ,two late ,pleistocene faunas from southwestern ,kansas4 ,contrib4 ,univ4 ,michigan ,mus4 ,paleo41 #af7a73a-bbc1 #af pls41 #ah figs4 ,,hibbard1 ,c4 ,w41 and ,,wilson1 ,j4 ,a4 #aiej4 ,a new rodent from subsurface stratum in ,bee ,county1 ,texas4 ,jour4 ,paleo41 #bd3fba-fbc1 ,september4 ,,hooper1 ,e4 ,t4 #aidf4 ,two genera of pocket gophers should be congeneric4 ,jour4 ,mamm41 #bg3cig-cii1 ,november1 #aife4 ,,james1 ,g4 ,t4 #aifc4 ,paleontology and nonmarine stratigraphy of the ,cuyama ,valley ,badlands1 ,california4 ,part ,i4 ,geology1 faunal interpretations1 and systematic descriptions of ,chiroptera1 ,insectivora1 and ,rodentia4 ,univ4 ,california ,publ4 ,geol4 ,sci41 #de3;iv #agj1 #h pls41 #ec figs41 ,june #bf4 ,,johnson1 ,c4 ,s41 and ,,savage1 ,d4 ,e4 #aiee4 ,a survey of various ,late ,cenozoic vertebrate faunas of the ,panhandle of ,texas1 ,part ,i4 ,univ4 ,california ,publ4 ,geol4 ,sci41 #ca3bg-ej4 ,,kendeigh1 ,c4 ,s4 #aifa4 ,animal ,ecology4 ,prentice ,hall1 ,inc41 ,englewood ,clifts1 ,new ,jersey1 pp4 x #dfh4 ,,kurten1 ,b4 #aife4 ,the ,pleistocene ,felidae of ,florida4 ,bull4 ,florida ,state ,mus41 #i7f73bae-bgc1 ,june #h4 ,,leidy1 ,j4 #ahfi4 ,the extinct mammalian fauna of ,dakota and ,nebraska--together with a synopsis of the mammalian remains of ,north ,america4 ,philadelphia1 #dgb pp41 #cj pls4 ,,macdonald1 ,j4 ,r4 #aifc4 ,the ,miocene faunas from the ,wounded ,knee area of western ,north ,dakota4 ,bull4 ,amer4 ,mus4 ,nat4 ,hist41 #abe3ada-cbh1 #cj figs41 ,august #bf4 ,,maldonado-,,koerdell1 ,m4 #aidh4 ,los vertebrados fosiles del ,cuaternario en ,mexico4 ,rev4 ,soc4 ,mex4 ,hist4 ,nat41 #i3a-ce1 ,june4 ,,marsh1 ,o4 ,c4 #ahga4 ,notice of some new fossil mammals and birds from the ,tertiary formations of the west4 ,amer4 ,jour4 ,sci4 and ,art1 #c3abj-abg4 ,,matthew1 ,w4 ,d4 #ahii4 ,a provisional classification of the fresh-water ,tertiary of the ,west4 ,bull4 ,amer4 ,mus4 ,nat4 ,hist41 #ab3ai-ge1 ,march #ca4 #aijb4 ,list of the ,pleistocene fauna from ,hay ,springs1 ,nebraska4 ,bull4 ,amer4 ,mus4 ,nat4 ,hist41 #af3cag-cbb1 ,september #be4 #aiji4 ,faunal lists of the ,tertiary mammalia of the west4 ,bull4 ,u4 ,s4 ,geol4 ,surv41 #cfa3ia-ach4 #aiaj4 ,notes on the osteology and relationships of ,paramys1 and the affinities of the ,ischyromyidae4 ,bull4 ,amer4 ,mus4 ,nat4 ,hist41 #bh3 #dc-gb1 #ai figs41 ,march #bb4 #aibc;a4 ,fossil bones in the rock4 ,the fossil quarry near ,agate1 ,sioux ,county1 ,nebraska4 ,nat4 ,hist41 #bc3ceh-cfi4 #aibc;b4 ,the occurrence of the ,hesperopithecus tooth4 ,amer4 ,mus4 ,novit41 #ec3aa-ac1 ,january #f4 #aibd4 ,third ,contribution to the ,snake ,creek ,fauna4 ,bull4 ,amer4 ,mus4 ,nat4 ,hist41 #ej3ei-baj1 ,july #c4 ,,matthew1 ,w4 ,d41 and ,,cook1 ,h4 ,j4 #aiji4 ,a ,pliocene fauna from western ,nebraska4 ,bull4 ,amer4 ,mus4 ,nat4 ,hist41 #bf3cfa-dad4 ,,mayer-,,oakes1 ,w4 ,j4 #aiei4 ,a stratigraphic excavation at ,el ,risco1 ,mexico4 ,proc4 ,amer4 ,phil4 ,soc41 #ajc3ccb-cgc1 ,june #ae1 #aiei4 ,,mcgrew1 ,p4 ,o4 #aidd4 ,an early ,pleistocene 7,blancan7 fauna from ,nebraska4 ,field ,mus4 ,nat4 ,hist41 ,geol4 ,ser41 #i7b73cc-ff1 ,january #bj4 ,,merriam1 ,c4 ,h4 #ahie4 ,monographic revision of the pocket gophers1 family ,geomyidae 7exclusive of the species of ,thomomys74 ,n4 ,amer4 ,fauna1 #h3a-beh1 #ai pls41 #d maps1 #ha figs41 ,january #ca4 ,,miller1 ,g4 ,s41 ,,jr41 and ,,gidley1 ,j4 ,w4 #aiah4 ,synopsis of the supergeneric groups of rodents4 ,jour4 ,washington ,acad4 ,sci41 #h3dca-ddh1 ,july #ai4 ,,miller1 ,g4 ,s41 ,,jr41 and ,,kellogg1 ,r4 #aiee4 ,list of ,north ,american ,recent mammals4 ,bull4 ,u4 ,s4 ,nat4 ,mus41 #bje3xii #ied1 ,march #c4 ,,mooser1 ,o4 #aiei4 ,la fauna ,cedazo del ,pleistoceno en ,aguascalientes4 ,an4 ,inst4 ,biol4 ,mex41 #bi7a and #b73dji-deb1 #bi figs4 ,,paulson1 ,g4 ,r4 #aifa4 ,the mammals of the ,cudahy fauna4 ,papers ,michigan ,acad4 ,sci41 ,arts1 and ,letters1 #df3abg-aec4 ,,peters1 ,w4 #ahgd4 ,uber die ,taschenmause und eine neue ,art derselben1 ,heteromys adspersus1 aus ,panama4 ,monatsber4 ,k4 ,acad4 ,wissensch4 ,berlin1 pp4 #ced-cei1 #a pl4 ,,ray1 ,c4 ,e4 #aieh4 ,additions to the ,pleistocene mammalian fauna from ,melbourne1 ,florida4 ,bull4 ,mus4 ,comp4 ,zool41 #aai3dba-ddi1 #e figs41 ,november4 ,,russell1 ,r4 ,j4 #aifj4 ,pleistocene pocket gophers from ,san ,josecito ,cave1 ,nuevo ,len1 ,mxico4 ,univ4 ,kansas ,publ41 ,mus4 ,nat4 ,hist41 #i3eci-edh1 ,january #ad4 ,,savage1 ,d4 ,e4 #aiea4 ,late ,cenozoic vertebrates of the ,san ,francisco ,bay ,region4 ,univ4 ,california ,publ4 ,geol4 ,sci41 #bh3bae-cad1 ,march #bc4 ,,schultz1 ,c4 ,b41 and ,,howard1 ,e4 ,b4 #aice4 ,the fauna of ,burnet ,cave1 ,guadalupe ,mountains1 ,new ,mexico4 ,proc4 ,acad4 ,nat4 ,sci4 ,philadelphia1 #hg3bgc-bih1 #cg figs41 #f pls4 ,,schultz1 ,c4 ,b41 ,,lueninghoener1 ,g4 ,c41 and ,,frankforter1 ,w4 ,d4 #aiea4 ,a graphic rsum of the ,pleistocene of ,nebraska4 ,bull4 ,univ4 ,nebraska ,state ,mus41 #c7f73a-da1 ,july4 ,,schultz1 ,c4 ,b41 and ,,stout1 ,t4 ,m4 #aidh4 ,pleistocene mammals and terraces in the ,great ,plains4 ,bull4 ,geol4 ,soc4 ,amer41 #ei3eec-ehi1 ,june4 ,,schultz1 ,c4 ,b41 and ,,tanner1 ,l4 ,g4 #aieg4 ,medial ,pleistocene fossil vertebrate localities in ,nebraska4 ,univ4 ,nebraska ,state ,mus41 #d7d73ei-ha1 ,september4 ,,schultz1 ,g4 ,e4 #aife4 ,pleistocene vertebrates from the ,butler ,springs local fauna1 ,meade ,county1 ,kansas4 ,papers ,michigan ,acad4 ,sci41 ,arts1 and ,letters1 #ej3bce-bfe4 ,,schultz1 ,j4 ,r4 #aich4 ,a late ,quaternary mammal fauna from the tar seeps of ,mc,kittrick1 ,california4 ,carnegie ,inst4 ,washington ,publ41 #dhg3aaa-bae1 ,july #f4 ,,shotwell1 ,j4 ,a4 #aief4 ,hemphillian mammalian assemblage from northeastern ,oregon4 ,bull4 ,geol4 ,soc4 ,amer41 #fg3gag-gch1 #g figs41 ,june4 #aifc4 ,the ,juntura ,basin3 studies in earth history and paleoecology4 ,mammalian fauna of the ,drewsey ,formation1 ,bartlett ,mountains1 ,drinkwater and ,otis ,basin local faunas4 ,trans4 ,amer4 ,phil4 ,soc41 n4s41 #ec7a73a-gg1 ,april4 ,,simpson1 ,g4 ,g4 #aibh4 ,pleistocene mammals from a cave in ,citrus ,county1 ,florida4 ,amer4 ,mus4 ,novit41 #cbh3a-d1 ,october #bf4 #aibi4 ,pleistocene ,mammalian fauna of the ,seminole ,field1 ,pinellas ,county1 ,florida4 ,bull4 ,amer4 ,mus4 ,nat4 ,hist41 #ef3efa-eii4 #aide4 ,the principles of classification and a classification of mammals4 ,bull4 ,amer4 ,mus4 ,nat4 ,hist41 #he3 pp4 xvi #cej1 ,october #e4 #aiec4 ,the major features of evolution4 ,columbia ,univ4 ,press1 ,new ,york1 pp4 xx #dcd1 #eb figs4 ,,sinclair1 ,w4 ,j4 #aije4 ,new ,mammalia from the ,quaternary caves of ,california4 ,bull4 ,dept ,geol4 ,univ4 ,california1 #d3ade-afa1 pls4 #ai and #bc4 ,,skinner1 ,m4 ,f4 #aidb4 ,the fauna of ,papago ,springs ,cave1 ,arizona4 ,bull4 ,amer4 ,mus4 ,nat4 ,hist41 #hj3adc-bbj1 ,november #f4 ,,slaughter1 ,b4 ,h41 and ,,hoover1 ,b4 ,r4 #aifc4 ,sulphur ,river ,formation and the ,pleistocene mammals of the ,ben ,franklin local fauna4 ,jour4 ,grad4 ,resc4 ,center1 #ca7c73acb-adh1 ,june4 ,,slaughter1 ,b4 ,h41 and ,,ritchie1 ,f4 #aifc4 ,pleistocene mammals of the ,clear ,creek local fauna1 ,denton ,county1 ,texas4 ,jour4 ,grad4 ,resc4 ,center1 #ca7c73aag-aca1 ,june4 ,,starrett1 ,a4 #aief4 ,pleistocene mammals of the ,berends fauna of ,oklahoma4 ,jour4 ,paleo41 #cj3aahg-aaib4 ,,stephens1 ,j4 ,j4 #aifj4 ,stratigraphy and paleontology of a late ,pleistocene ,basin1 ,harper ,co41 ,oklahoma4 ,bull4 ,geol4 ,soc4 ,amer41 #ga3afge-agjb1 ,november4 ,,strain1 ,w4 ,s4 #aiff4 ,blancan mammalian fauna and ,pleistocene formations1 ,hudspeth ,county1 ,texas4 ,bull ,texas ,memorial ,mus41 #aj3a-ee1 #h figs41 #ac pls41 ,february4 ,,tamsitt1 ,j4 ,r4 #aieg4 ,peromyscus from the ,late ,pleistocene of ,texas4 ,the ,texas ,jour4 ,sci41 #i7c73cee-cfc1 ,september4 ,,waterhouse1 ,g4 ,r4 #ahci4 ,observations on the ,rodentia1 with a view to point out the groups1 as indicated by the structure of the crania1 in this order of mammals4 ,mag4 ,nat4 ,hist41 new series1 #c3ij-if1 #ahd-ahh1 #bgd-bgi1 #eic-fjj1 #a pl4 #ahda4 ,observations on the ,rodentia4 ,ann4 ,mag4 ,nat4 ,hist41 #h3ha-hd1 pl4 #b4 #ahdh4 ,a natural history of the mammalia4 ,vol4 #b1 containing the order ,rodentia1 or gnawing mammalia4 ,hippolyte ,bailliere1 ,london1 #ejj pp41 #ba pls4 ,,waters1 ,j4 ,h4 #aieg4 ,second find of ,thomomys talpoides from late ,pleistocene in ,kansas4 ,jour4 ,mamm41 #cg3edj-edb4 ,,white1 ,j4 ,a41 and ,,downs1 ,t4 #aifa4 ,a new ,geomys from the ,vallecito ,creek ,pleistocene of ,california1 with notes on variation in ,recent and fossil species4 ,contr4 in ,science1 ,los ,angeles ,co4 ,mus41 #db3a-cd1 ,june #cj4 ,,wilson1 ,r4 ,w4 #aicc;a4 ,pleistocene mammalian fauna from the ,carpinteria asphalt4 ,carnegie ,inst4 ,washington ,publ41 #ddj3ei-gf1 ,november4 #aicc;b4 ,a rodent fauna from the later ,cenozoic beds of southwestern ,idaho4 ,carnegie ,inst4 ,washington ,publ4 #ddj3aag-ace1 #h figs41 #b pls41 ,december4 #aicf4 ,a ,pliocene rodent fauna from ,smith's ,valley1 ,nevada4 ,carnegie ,inst4 ,washington ,publ41 #dgc3ae-cd4 #aicg4 ,pliocene rodents of western ,north ,america4 ,carnegie ,inst4 ,washington ,publ4 #dhg3ba-gc1 ,july #bc4 #aidj4 ,two new ,eocene rodents from ,california4 ,carnegie ,inst4 ,washington ,publ41 #ead3he-ie1 ,june #bg4 #aidi4 ,early ,tertiary rodents of ,north ,america4 ,carnegie ,inst4 ,washington ,publ41 #ehd3fg-afd1 ,june #bb4 ,,winge1 ,h4 #aibd4 ,pattedyr-,slaegter4 ,vol4 #b1 ,rodentia1 ,carnivora1 ,primates4 ,h4 ,hagerups ,forlag1 ,copenhagen1 #cba pp4 ,,wood1 ,a4 ,e4 #aice4 ,evolution and relationship of the heteromyid rodents4 ,ann4 ,carnegie ,mus41 #bd3gc-bfb1 ,may #ac4 #aicf4 ,geomyid rodents from the ,middle ,tertiary4 ,amer4 ,mus4 ,novit41 #hff3a-ca1 ,july #b4 #aiej4 ,a new geomyid rodent from the ,miocene of ,montana4 ,ann4 ,carnegie ,mus41 #ca3cce-cch1 #a fig4 #aiee4 ,a ,revised classification of rodents4 ,jour4 ,mamm41 #cf3afe-ahg1 ,may #bf4 ,,wood1 ,a4 ,e41 and ,,wilson1 ,r4 ,w4 #aicf4 ,a suggested nomenclature for the cusps of the cheek teeth of rodents4 ,jour4 ,paleo41 #aj3chh-cia1 #b figs41 ,july4 ,transmitted ,may #bi1 #aifg4 99 99 99 99 99 ,transcriber's note3 ,all obvious typographical errors were corrected4 ,minor changes were made to standardize the text to match the most prevalent form used4 ,typographical ,corrections ,page ,correction #dgg cumberlandicus cumberlandius #ece breath breadth