,university of ,kansas ,publications ,museum of ,natural ,history ,volume #ab1 ,no4 #b1 pp4 #aee-ahj1 #aj figs4 -----------,july #aj1 #aiei--------------- ,the ,ancestry of ,modern ,amphibia3 ,a ,review of the ,evidence ,,by ,,theodore ,h4 ,,eaton1 ,,jr4 ,university of ,kansas ,lawrence #aiei ,university of ,kansas ,publications1 ,museum of ,natural ,history ,editors3 ,e4 ,raymond ,hall1 ,chairman1 ,henry ,s4 ,fitch1 ,robert ,w4 ,wilson ,volume #ab1 ,no4 #b1 pp4 #aee-ahj ,published ,july #aj1 #aiei ,university of ,kansas ,lawrence1 ,kansas ,,printed ,,in ,,the ,,state ,,printing ,,plant ,,topeka1 ,,kansas #aiei ,illustration #bg-hcfb ,transcriber's ,notes3 ,several typos have been regulated4 ,one typo of ancester for ancestor was corrected4 ,one instance of salamanderlike corrected to salamaner-like4 ,the ,ancestry of ,modern ,amphibia3 ,a ,review of the ,evidence ,,by ,,theodore ,h4 ,,eaton1 ,,jr4 ,,introduction ,in trying to determine the ancestral relationships of modern orders of ,amphibia it is not possible to select satisfactory structural ancestors among a wealth of fossils1 since very few of the known fossils could even be considered possible1 and scarcely any are satisfactory1 for such a selection4 ,the nearest approach thus far to a solution of the problem in this manner has been made with reference to the ,anura4 ,watson's paper 7#aidj71 with certain modifications made necessary by ,gregory 7#aiej71 provides the paleontological evidence so far available on the origin of frogs4 ,it shows that several features of the skeleton of frogs1 such as the enlargement of the interpterygoid spaces and orbits1 reduction of the more posterior dermal bones of the skull1 and downward spread of the neural arches lateral to the notochord1 were already apparent in the ,pennsylvanian ,amphibamus 7,fig4 #a71 with which ,gregory synonymized ,miobatrachus and ,mazonerpeton4 ,but between the ,pennsylvanian and the ,triassic 7the age of the earliest known frog1 ,protobatrachus7 there was a great lapse of time1 and that which passed between any conceivable ,paleozoic ancestor of ,urodela and the earliest satisfactory representative of this order 7in the ,cretaceous7 was much longer still4 ,the ,apoda1 so far as known1 have no fossil record4 ,nevertheless it should be possible1 first1 to survey those characters of modern ,amphibia that might afford some comparison with the early fossils1 and second1 to discover among the known ,paleozoic kinds those which are sufficiently unspecialized to permit derivation of the modern patterns4 ,further circumstantial evidence may be obtained by examining some features of ,recent ,amphibia which could not readily be compared with anything in the fossils2 such are the embryonic development of the soft structures1 including cartilaginous stages of the skeleton1 the development and various specializations of the ear mechanism1 adaptive characters associated with aquatic and terrestrial life1 and so on4 ,,comparison ,,of ,,modern ,,orders ,,with ,,the ,,labyrinthodonts ,,and ,,lepospondyls ,illustration3 ,fig4 #a4 ,saurerpeton 7x #a_/b1 after ,romer1 #aicj1 fig4 #f72 ,amphibamus1 the palatal view x #b-a_/d1 from ,watson1 #aidj1 fig4 #d 7as ,miobatrachus71 the dorsal view x #b-a_/b1 from ,gregory's revised figure of ,amphibamus 7#aiej1 ,fig4 #a72 ,protobatrachus1 x #a1 from ,watson1 #aidj1 fig4 #ah1 #ai4 ,in both ,anura and ,urodela the skull is short1 broad1 relatively flat1 with reduced pterygoids that diverge laterally from the parasphenoids leaving large interpterygoid vacuities1 and with large orbits4 7,these statements do not apply to certain larval or perennibranchiate forms47 ,the skull in both orders has lost a number of primitive dermal bones in the posterior part2 these are3 basioccipital1 supraoccipital1 postparietal1 intertemporal1 supratemporal1 and tabular4 ,the exoccipitals form the two condyles but there are no foramina for the #aath and #abth nerves1 since these are not separate in modern ,amphibia4 ,the opisthotic is missing in all except ,proteidae 7but see discussion of the ear74 ,although the skull is normally autostylic1 a movable basipterygoid articulation is present among ,hynobiid salamanders and in at least the metamorphic stages of primitive frogs1 and therefore should be expected in their ancestors4 ,the vertebrae are1 of course1 complete2 see discussion in later section4 ,the quadratojugal1 lost in salamanders1 is retained in frogs1 and conversely the lacrimal1 absent in frogs1 occurs in a few primitive salamanders4 ,the situation in ,apoda is different1 but postfrontal and jugal should be noted as bones retained in this order while lost in the others4 ,thus1 in spite of minor differences1 the above list shows that there are numerous and detailed similarities between ,anura and ,urodela with respect to the features in which they differ from the ,paleozoic orders4 ,pusey 7#aidc7 listed #bf characters which ,ascaphus shares with salamanders but not with more advanced frogs2 a few of these might be coincidental1 but most of them are of some complexity and must be taken to indicate relationship4 ,the main adaptive specializations of ,anura1 however1 including loss of the adult tail1 extreme reduction in number of vertebrae1 formation of urostyle1 elongation of the ilium and lengthening of the hind legs1 must have appeared at a later time than the separation of that order from any possible common stem with ,urodela1 although they are only partially developed in the ,triassic ,protobatrachus4 ,turning to the ,paleozoic ,amphibia1 there are two groups in which some likelihood of a relationship with modern order exists4 ,in the ,pennsylvanian ,trimerorhachoidea 7,labyrinthodontia1 order ,temnospondyli7 some members1 such as ,eugyrinus1 ,saurerpeton1 and notably ,amphibamus 7,fig4 #a7 had short1 broad heads1 an expansion of palatal and orbital openings1 posterior widening of the parasphenoid associated with divergence of the pterygoids1 a movable basipterygoid articulation1 and reduction in size 7but not loss7 of the more posterior dermal bones of the skull4 ,in recognition of ,watson's 7#aidj7 evidence that these animals make quite suitable structural ancestors of frogs1 ,romer 7#aide7 placed ,amphibamus in an order1 ,eoanura1 but ,gregory 7#aiej7 indicated that it might better be left with the temnospondyls4 ,association of the urodele stem with this group does not seem to have been proposed hitherto4 ,the other group of ,paleozoic ,amphibia that has been considered probably ancestral to any modern type is the subclass ,lepospondyli1 containing three orders1 ,aistopoda1 ,nectridia and ,microsauria4 ,in these the vertebrae are complete 7holospondylous71 the centra presumably formed by cylindrical ossification around the notochord1 and there is no evidence as to the contributions from embryonic cartilage units4 ,it is important to note at this point that precisely the same statement can be made regarding the vertebrae of adults of all three ,recent orders1 yet for all of them1 as shown in a later section1 we have ample evidence of the part played by cartilage elements in vertebral development4 ,therefore 7a7 we cannot say that there were no such elements in embryonic stages of lepospondyls1 and 7b7 it would take more than the evidence from adult vertebrae to relate a particular modern order 7for example1 ,urodela7 to the ,lepospondyli4 ,vague similarities to ,urodela have been noted by many authors in the ,nectridia1 ,aistopoda and ,microsauria1 but these are not detailed and refer mainly to the vertebrae4 ,the skulls do not show1 either dorsally or in the palate1 any striking resemblance to those of generalized salamanders1 and certainly most known lepospondyls are too specialized to serve as the source of ,urodela4 ,it is true that the elongate bodies1 small limbs1 and apparent aquatic habitus of some lepospondyls accord well with our usual picture of a salamander1 but such a form and way of life have appeared in many early ,amphibia1 including the labyrinthodonts4 ,the family ,lysorophidae 7,fig4 #b71 usually placed among microsaurs1 is sufficiently close in skull structure to the ,apoda to be a possible ancestor of these1 but it probably has nothing to do with ,urodela1 by reason of the numerous morphological specializations that were associated with its snakelike habitus4 ,illustration3 ,fig4 #b4 ,lysorophus tricarinatus1 lateral and posterior views x #b-a_/b1 modified after ,sollas1 #aibj1 ,figs4 #h and #ab1 respectively2 palatal view after ,broom1 #aiah1 x #a-a_/b4 ,for explanation of abbreviations see ,fig4 #c4 ,mc,dowell's 7#aieh7 suggestion that it would be profitable to look among the ,seymouriamorpha for the ancestors of frogs seems to be based upon a few details of apparent resemblance rather than a comprehensive view of the major characters of the animals4 ,in most points which he mentions 7limb girdles1 form of ear1 pterygoid articulation7 the present writer does not see a closer similarity of frogs to ,seymouriamorpha than to ,temnospondyli4 ,still other opinions have been expressed4 ,herre 7#aice71 for instance1 concludes on anatomical1 biological and paleontological grounds that the orders of ,urodela1 ,anura1 ,apoda and ,stegocephali were all independently evolved from fish1 but beyond citing the opinions of a number of other authors he does not present tangible evidence for this extreme polyphyletic interpretation4 ,more notable are the views of several ,scandinavian workers 7,saeve-,soederbergh1 #aicd2 ,jarvik1 #aidb2 ,holmgren1 #aicc1 #aici1 #aidi;a1 b71 of whom ,jarvik1 in a thorough analysis of the ethmoid region1 would derive the ,urodela from ,porolepid ,crossopterygii1 and all other tetrapods from the ,rhipidistia2 ,saeve-,soederbergh and ,holmgren1 the latter using the structure of carpus and tarsus1 see a relationship of ,urodela to ,dipnoi1 but accept the derivation of labyrinthodonts and other tetrapods from ,rhipidistia4 ,all of this work is most detailed and laborious1 and has produced a great quantity of data useful to morphologists1 but the diphyletic theory is not widely adopted2 the evidence adduced for it seems to consist largely of minutiae which1 taken by themselves1 are inconclusive1 or lend themselves to other interpretation4 ,for instance ,holmgren's numerous figures of embryonic limbs of salamanders show patterns of cartilage elements that he would trace to the ,dipnoan type of fin1 yet it is difficult to see that the weight of evidence requires this1 when the pattern does not differ in any fundamental manner from those seen in other embryonic tetrapods1 and the differences that do appear may well be taken to have ontogenetic rather than phylogenetic meaning4 ,further1 the ,dipnoan specialization of dental plates and autostylic jaw suspension1 already accomplished early in the ,devonian1 would seem to exclude ,dipnoi from possible ancestry of the ,urodela1 an order unknown prior to the ,mesozoic1 in which the teeth are essentially similar to those of late ,paleozoic ,amphibia1 and the jaw suspension is not yet in all members autostylic4 ,,the ,,ear ,illustration3 ,fig4 #c4 ,occipital region of skulls of ,megalocephalus brevicornis 7x #c_/aj1 after ,watson1 #aibf1 as ,orthosaurus71 ,dvinosaurus 7x #a_/d1 modified after ,bystrow1 #aich2 the lower figure after ,sushkin1 #aicf71 and ,necturus maculosus 7x #c1 original1 from ,k4 ,u41 ,no4 #cdga74 ,abbreviations ,used in ,figures b'd4c4--basidorsal cartilage 7neural arch7 b'oc4--basioccipital ce4#a-d--;centrale#a-d ch4--ceratohyal clav4--clavicle clei4--cleithrum cor4--coracoid d4c4#a-d--;distal carpal#a-d diap4--diapophysis exoc4--exoccipital ep4--episternum hyost4--hyostapes i4--intermedium ,mk4--,meckel's cartilage n4--notochord om4--omosternum op4--operculum opis4--opisthotic par4--parietal par4 proc4--paroccipital process peri4 cent4--perichordal centrum p'p4--postparietal prep4--prepollex pro4--prootic p'sp4--parasphenoid pt4--pterygoid p4t4f4--post-temporal fossa postzyg4--postzygapophysis qj4--quadratojugal qu4--quadrate ra4--radiale r4hy4--hyomandibular ramus of ,,vii rib-b4--rib-bearer r4md4--mandibular ramus of ,,vii sc4--scapula sc'cor4--scapulocoracoid s'd4--supradorsal cartilage s'd47postzyg47--supradorsal 7postzygapophysis7 soc4--supraoccipital sp4c4--spinal cord sq4--squamosal s'sc4--suprascapula s't4--supratemporal sta4--stapes ster4--sternum tab4--tabular uln4--ulnare v4a4--vertebral artery xiph4--xiphisternum ,i1,,iv--digits ,i and ,,iv ,v1 ,,vii1 ,x1 ,,xii--foramina for cranial nerves of these numbers 7in ,fig4 #d1 ,,vii is the facial nerve7 ,in temnospondylous ,amphibia the tympanum generally occupied an otic notch1 at a high level on the skull1 bordered dorsomedially by the tabular and ventrolaterally by the squamosal4 ,in this position the tympanum could receive airborne sounds whether the animal were entirely on land or lying nearly submerged with only the upper part of its head exposed4 ,among those ,anura in which the ear is not reduced the same is true1 except that the tabular is lost4 ,in ,temnospondyli 7,fig4 #c7 the posterior wall of the otic capsule was usually formed by the opisthotic1 which extended up and outward as a buttress from the exoccipital to the tabular1 and sometimes showed a paroccipital process for the insertion1 presumably1 of a slip or tendon of the anterior axial musculature4 ,the stapes1 in addition to its foot in the fenestra ovalis and its tympanic or extrastapedial process to the tympanum1 bore a dorsal process 7or ligament7 to the tabular1 an internal process 7or ligament7 to the quadrate or an adjacent part of the squamosal1 and a ligament to the ceratohyal4 ,some of these attachments might be reduced or absent in special cases1 but they seem to have been the ones originally present both phylogenetically and embryonically in ,amphibia4 ,among typical frogs 7,fig4 #d7 the base1 or otostapes1 is present and bony1 the extrastapedial process 7extracolumella1 or hyostapes7 is usually cartilaginous1 the dorsal process 7processus paroticus7 is of cartilage or ligament1 but the other two attachments are absent in the adult4 ,the exoccipital extends laterally1 occupying the posterior face of the otic capsule4 ,between it and the otostapes is a small disc1 usually ossified1 the operculum1 which normally fits loosely in a portion of the fenestral membrane1 and is developed from the otic capsule4 ,the opercularis muscle extends from this disc to the suprascapula1 in many but by no means all families of ,anura4 ,illustration3 ,fig4 #d4 ,diagram of middle ear structures in ,rana 7upper figure1 after ,stadtmueller1 #aicf1 and lower left after ,de,beer1 #aicg71 and ,ambystoma 7lower right1 after ,de,beer1 #aicg72 all x #d4 ,for explanation of abbreviations see ,fig4 #c4 ,among ,urodela 7,fig4 #d7 the middle ear cavity and tympanum are lacking1 and the stapes 7columella7 consists of no more than its footplate and the stylus1 which is attached to the border of the squamosal1 thus corresponding to the internal process4 ,in families in which individuals metamorphose and become terrestrial 7,hynobiidae1 ,ambystomidae1 ,salamandridae1 ,plethodontidae71 an operculum and opercularis muscle appear in the adult1 just as in frogs1 except that in ,plethodontidae1 the most progressive family1 the operculum fuses with the footplate of the stapes4 ,among neotenous or perennibranchiate urodeles there is no separate operculum or opercularis4 ,the evidence given by ,reed 7#aiae7 for fusion of the operculum with the columella in ,necturus appears inconclusive1 in spite of the great care with which his observations were made4 ,on the other hand1 ,necturus and ,proteus alone among living salamanders have a distinct opisthotic on the posterior wall of the otic capsule 7,fig4 #c71 as do the ,cretaceous ,hylaeobatrachus and the ,eocene ,palaeoproteus4 ,probably these ,proteidae should be regarded as primitive in this respect1 although many other features may be attributed to neoteny4 ,there is a contrast between ,anura and most ,urodela in the relative positions of the stapes and facial nerve1 as shown in ,de,beer's 7#aicg7 diagrams4 ,in the latter 7,ambystoma7 the nerve is beneath1 and in the former 7,rana7 above1 the stapes4 ,judging by figures of ,neoceratodus1 ,hypogeophis1 and several types of reptiles and mammals1 the ,urodela are exceptional4 ,necturus1 however1 has the nerve passing above its stapes1 and this may be primitive in the same sense as the persistent opisthotic4 ,there can be1 of course1 no question of the nerve having worked its way through or over the obstructing stapes in order to come below it in salamanders2 rather1 the peripheral growth of neuron fibers in the embryo must simply pursue a slightly different course among the partially differentiated mesenchyme in the two contrasting patterns4 ,although ,de,beer 7#aicg7 shows in his figure of ,hypogeophis 7one of the ,apoda7 an operculum1 this is apparently a mistake4 ,the stapes has a large footplate1 and its stylus articulates with the quadrate1 but no true operculum or opercularis has been described in the ,apoda4 ,the facial nerve passes above the stapes4 ,it does not seem necessary to regard the conditions in this order as related directly to those of either salamanders or frogs1 but a reduction of the stapes comparable to that in salamanders has occurred4 ,the presence in both frogs and terrestrial salamanders of a special mechanism involving the opercularis muscle and an operculum cut out in identical fashion from the wall of the otic capsule behind the stapes seems to require some other explanation than that of a chance convergence or parallelism4 ,although the stapes and otic region are readily visible in a number of labyrinthodonts and lepospondyls1 no indication of an operculum seems to be reported among them4 ,but in the ,triassic ,protobatrachus 7,fig4 #a71 which is unmistakably a frog in its skull1 pelvis and some other features1 ,piveteau 7#aicg7 has shown1 immediately behind the foot of the stapes1 a small bony tubercle1 which he and ,watson 7#aidj7 designated opisthotic4 ,very clearly it served for insertion of a muscle1 and it is equally clear that the bone is a reduced opisthotic1 carrying the paroccipital process already mentioned as characteristic of it in some temnospondyls4 ,since the remainder of the posterior wall of the otic capsule consists of cartilage1 meeting the exoccipital1 it may be that the opisthotic becomes the operculum in frogs4 ,protobatrachus was too far specialized in the ,anuran direction1 although it still had a tail1 and the forelegs and hind legs were nearly the same size1 to be considered a possible ancestor of the ,urodeles4 ,but at one stage in the general reduction of the skull in the ancestry of both groups1 a condition similar to that in ,protobatrachus may have characterized the otic region1 long before the ,triassic4 ,in the argument thus far we have considered terrestrial1 adult amphibians1 since it is only in these that either the normal middle ear and tympanum1 or the opercular apparatus1 is present4 ,but among the urodeles several neotenic types occur 7this term applies also to the perennibranchs74 ,for most of these there is nothing about the otic region that would be inconsistent with derivation1 by neoteny1 from known families in which adults are terrestrial2 for example1 ,cryptobranchus could have had a ,hynobiid-like ancestor4 ,but this1 as mentioned above1 does not hold for the ,proteidae1 which possess an opisthotic of relatively large size1 distinctly separate from the exoccipital and prootic4 ,either this bone is a neomorph1 which seems improbable1 or there has not been in the ancestry of this particular family an episode of reduction comparable to that seen in the terrestrial families1 where there is an operculum instead of a normal opisthotic4 ,therefore the ,proteidae probably are not derived from the general stem of other salamanders1 but diverged sufficiently long ago that the bones of the otic region were reduced on a different pattern4 ,they need not be removed from the order1 but1 in this respect1 recognized as more primitive than any other existing ,urodela or ,anura4 ,a recent paper by ,hecht 7#aieg7 discusses many features of ,necturus and ,proteus1 and shows that they are remote from each other2 his evidence does not seem to prove1 however1 that they were of independent origin or that they need be placed in separate families4 ,,vertebrae ,,and ,,ribs ,development of the vertebrae and ribs of ,recent ,amphibia has been studied by ,gamble 7#aibb71 ,naef 7#aibi71 ,mookerjee 7#aicj a1 b71 ,gray 7#aicj7 and ,emelianov 7#aicf71 among others4 ,mac,bride 7#aicb7 and ,remane 7#aich7 provide good summaries4 ,in this section reference will be made to the embryonic vertebral cartilages by the names used for them in these studies1 although the concept of arcualia is currently considered of little value in comparative anatomy4 ,illustration3 ,fig4 #e4 ,development of ,anuran vertebrae4 ,upper left1 late tadpole of ,xenopus laevis2 lower left1 same just after metamorphosis2 upper right1 diagram of general components of primitive ,anuran vertebra4 7,after ,mac,bride1 #aicb1 ,figs4 #ce1 #ch1 #dg;,d1 respectively47 ,lower right1 section through anterior portion of urostyle1 immediately posterior to sacral vertebra1 in transforming ,ascaphus truei 7original1 from specimen collected on ,olympic ,peninsula1 ,washington74 ,all x #bj approx4 ,for explanation of abbreviations see ,fig4 #c4 ,the centrum in ,anura 7,fig4 #e7 is formed in the perichordal sheath 7,rana1 ,bufo7 or only in the dorsal portion thereof 7,bombinator1 ,xenopus74 ,the neural arch develops from the basidorsal cartilages that rest upon1 and at first are entirely distinct from1 the perichordal sheath4 ,ribs1 present as separate cartilages associated with the #bnd1 #crd and #dth vertebrae in the larvae of ,xenopus and ,bombinator1 fuse with lateral processes 7diapophyses7 of the neural arches at metamorphosis1 but in ,leiopelma and ,ascaphus the ribs remain freely articulated in the adult4 ,basiventral arcualia have been supposed to be represented by the hypochord1 a median rod of cartilage beneath the shrinking notochord in the postsacral region1 which at metamorphosis ossifies to produce the bulk of the urostyle4 ,fig4 #e1 lower right1 a transverse section taken immediately posterior to the sacral ribs in a transforming specimen of ,ascaphus1 shows that the hypochord is a mass of cartilage formed in the perichordal sheath itself1 and very obviously is derived from the ventral part of postsacral perichordal centra2 there are1 then1 no basiventral arcualia1 and the discrete hypochord shown in ,mac,bride's diagram 7,fig4 #e1 upper right7 of a frog vertebra does not actually occur below the centrum1 but only below the notochord in the postsacral region4 ,illustration3 ,fig4 #f4 ,development of ,urodele vertebrae4 ,upper figures1 ,triton3 at left1 larva at #bj mm41 at right1 diagram of components of vertebra 7from ,mac,bride1 #aicb1 figs4 #ag1 #dg;,c74 ,middle figures1 ,molge vulgaris larva3 left1 at #ah mm42 middle1 at #bj-bb mm42 right1 at #be mm4 7from ,emelianov1 #aicf1 figs4 #cc1 #cf1 #ch respectively74 ,lower figures1 ,necturus maculosus larva3 left1 at #ba mm42 right1 at #bj mm4 7from ,mac,bride1 #aicb1 figs4 #da4e1 #da4c respectively1 after ,gamble1 #aibb74 ,all x #bj approx4 ,for explanation of abbreviations see ,fig4 #c4 ,in ,urodela 7,fig4 #f7 the pattern of vertebral and rib development is more complex1 and there has been much controversy over its interpretation4 ,neural arches and perichordal centra form in the same manner as in frogs1 but with the addition in certain cases 7,triton7 of a median supradorsal cartilage1 which gives rise to the zygapophyses of each neural arch4 ,difficulty comes1 however1 in understanding the relationship of the ribs to the vertebrae4 ,each rib1 usually two-headed1 articulates with a transverse process that in its early development seems to be separate from both the vertebra and the rib1 and is therefore known1 noncommittally1 as rib-bearer4 ,this lies laterally from the centrum1 neural arch1 and vertebral artery2 upon fusing with the vertebra it therefore encloses the artery in a foramen separate from the one between the capitulum and tuberculum of the rib 7the usual location of the vertebral artery74 ,at least four different interpretations of these structures have been suggested3 7#a7 ,naef 7#aibi7 considered the rib-bearer a derivative of the basiventral1 which1 by spreading laterally and dorsally to meet the neural arch1 enclosed the vertebral artery4 ,he then supposed that by reduction of the rib-bearer in other tetrapods 7frogs and amniotes7 the vertebrarterial foramen and costal foramen were brought together in a single foramen transversarium4 ,the implication is that the ,urodele condition is primitive1 but it cannot now be supposed that ,urodela are ancestral to any other group1 and the rib-bearer is most probably a specialization limited to salamanders4 ,this does not1 of course1 invalidate the first part of his interpretation4 7#b7 ,remane 7#aich71 noting that rib insertions of early ,amphibia are essentially as in ,amniota1 argued that the rib-bearer is not from the basiventral but is a neomorph which originates directly from the neural arch and grows ventrally4 ,this he inferred mainly from ,gamble's 7#aibb7 observation on ,necturus1 but his assumption that ,necturus is more primitive than other salamanders 7such as the ,salamandridae71 where the pattern differs from this1 is not necessarily correct4 ,rather1 the perennibranchs are distinguished mainly by their neotenous features1 and their development is likely to show simplifications which are not necessarily primitive4 ,the suggestion of a neomorph ought not to be made except as a last resort1 for it is simply an acknowledgment that the author does not recognize homology with any structure already known2 sometimes further information will make such recognition possible4 7#c7 ,gray 7#aicj71 using ,molge taeniatus1 concluded that the normal capitulum of the rib was lost1 but that the tuberculum bifurcated to make the two heads seen in ,urodela1 thus accounting for the failure of the costal foramen to coincide with that of the vertebral artery4 ,this answer1 too1 seems to entail an unprovable assumption which should not be made without explicit evidence4 7#d7 ,finally1 ,emelianov 7#aicf7 regarded the rib-bearer as a rudimentary ventral rib1 on account of its relationship to the vertebral artery1 and considered the actual rib to be a neomorph in the dorsal position characteristic of tetrapod ribs in general4 ,this argument would fit the ontogenetic picture satisfactorily1 provided that 7a7 there were some evidence of ventral1 rather than dorsal1 ribs in early ,amphibia1 and 7b7 we accept the invention of another neomorph in modern ,amphibia as an unavoidable necessity4 ,emelianov's conclusion 7p4 #beh7 should be quoted here 7translation73 ,the ribs of ,urodela are shown to be upper ribs1 yet we find besides these in ,urodela rudimentary lower ribs fused with the vertebral column4 ,the ribs of ,apoda are lower ribs4 ,in ,anura ribs fail to develop fully1 but as rare exceptions rudiments of upper ribs appear4 ,of these various interpretations1 that of ,naef seems to involve the minimum of novelty1 namely1 that the rib-bearer is the basiventral1 expanded and external to the vertebral artery4 ,it is not necessary to take this modification as the ancestral condition in tetrapods1 of course4 ,the basiventral 7intercentrum7 would merely have expanded sufficiently to provide a diapophysis for the tuberculum as well as the 7primitive7 facet for the capitulum4 ,no neomorph appears under this hypothesis1 which has the distinct advantage of simplicity4 ,figures of early stages in vertebral development by the authors mentioned show that the basidorsals chondrify first1 as neural arches1 while a separate mass of mesenchyme lies externally and ventrally from these4 ,this mesenchyme may chondrify either in one piece 7on each side7 or in two2 in ,molge the part adjacent to the centrum is ossified in the #bj-mm4 larva1 and subsequently unites with the more dorsal and lateral cartilaginous part1 while the rib1 appearing farther out1 grows inward to meet this composite rib-bearer4 ,in ,necturus the mesenchyme below the neural arch differentiates into a cartilage below the vertebral artery 7position proper to a basiventral71 a bridge between this and the neural arch1 and a rib1 the latter two chondrifying later than the basiventral proper4 ,in the axolotl 7presumably ,ambystoma tigrinum7 the rib-bearer grows downward from its first center of chondrification at the side of the neural arch 7,emelianov1 #aicf74 ,thus it appears that the simplest hypothesis to account for the rib-bearer is that 7a7 it is the basiventral1 7b7 it is recognizable just before chondrification as a mass of mesenchyme in contact with both the notochordal sheath and the basidorsal cartilage1 7c7 it may chondrify or ossify first in its ventral portion or in its dorsal portion1 the two then joining before it fuses with the rest of the vertebra1 7d7 the enclosure of the vertebral artery is a consequence of the extension of the basiventral beyond the position occupied by it in primitive ,amphibia1 and 7e7 there is no indication that this took place in other orders than the ,urodela4 ,it seems that the vertebrae in ,urodela have at least the following components3 perichordal centra1 separate basidorsal cartilages1 and basiventrals1 which are somewhat specialized in their manner of development4 ,the vertebrae of ,anura develop in the fashion just described except that basiventrals are lacking4 ,it would seem no more difficult to accept the derivation of salamander vertebrae from the temnospondylous type than it is in the case of frogs1 if other evidence points to such an ancestry4 ,illustration3 ,fig4 #g4 ,vertebrae of ,eusthenopteron 7x#a7 and ,ichthyostega 7x#b_/c1 after ,jarvik1 #aieb71 ,trimerorhachis 7x#a-a_/b1 after ,case71 and ,amphibamus 7x#aj1 after ,watson1 #aidj7 in lateral and end views2 the two lower right-hand figures are from ,watson 7#aidj1 as ,miobatrachus72 the lower left is from a cast of the ,miobatrachus specimen in ,chicago ,natural ,history ,museum1 ,no4 #bjjj1 in the presacral region 7original1 x#aj74 ,fig4 #g1 lower right1 is ,watson's 7#aidj7 illustration of the anterior trunk vertebrae of ,amphibamus 7,miobatrachus71 in which the intercentrum is shown as a single median piece4 ,fig4 #g1 lower left1 shows two of the more posterior trunk vertebrae seen as impressions in a cast of the type of ,miobatrachus romeri2 evidently the inter-centra were paired at about the level of the #afth vertebra1 and relatively large4 ,gregory's 7#aiej7 figure of the type specimen of ,mazonerpeton 7also equivalent to ,amphibamus7 shows the anterior trunk vertebrae in relation to the ribs essentially as they appear to me in the cast of ,miobatrachus1 and rather differently from ,watson's figure of the latter4 ,gregory is probably right in considering the specimens to represent various degrees of immaturity4 ,so far as present information goes1 then1 the vertebrae of salamanders and frogs show no clear evidence of derivation from those of any particular group among the early ,amphibia1 but their features are not inconsistent with a simplification of the pattern of ,temnospondyli4 ,illustration3 ,fig4 #h4 ,pectoral girdles of ,protobatrachus 7after ,piveteau1 #aicg71 ,notobatrachus 7after ,stipanicic and ,reig1 #aief71 ,ascaphus 7after ,ritland1 #aiee a7 and ,rana 7original72 all x#b4 ,for explanation of abbreviations see ,fig4 #c4 ,,pectoral ,,girdle ,hecht and ,ruibal 7,copeia1 #aibh3bdb7 make a strong point of the nature of the pectoral girdle in ,notobatrachus1 as described recently by ,stipanicic and ,reig 7#aiee1 #aief7 from the ,jurassic of ,patagonia1 and quite rightly recommend that the significance of the arciferal and firmisternal types of girdle be restudied4 ,that of ,notobatrachus is said to be firmisternal2 in view of the arciferal condition in the supposedly primitive ,leiopelma1 ,ascaphus1 ,bombinator1 etc41 this comes as a surprise4 ,is the firmisternal girdle1 as seen in ,rana1 ,bufo1 and others1 actually the ancestral type1 and has the arciferal been derived from something like this8 ,in the figures given by ,stipanicic and ,reig the ossified parts of the girdle are figured in detail 7,fig4 #h7 and ,reig's discussion of it is thorough4 ,the decision to call it firmisternal was taken with some hesitancy1 for no median elements are indicated1 and the position and shape of those seen is closely similar to the ossified parts in ,ascaphus and ,leiopelma2 there is no bony sternum or omosternum4 ,it is safe to suppose that some cartilage lay in the midline between the clavicles and coracoids1 but there is no evidence as to its extent1 rigidity1 or degree of overlapping if any4 ,apparently1 then1 there is not sufficient reason to infer that this ,jurassic frog had a pectoral girdle comparable with the modern firmisternal type4 ,piveteau 7#aiee3bfa7 remarks that the only living ,anuran that can be compared usefully with ,protobatrachus 7,triassic7 with regard to its pectoral girdle is ,ascaphus4 ,again1 the extent of cartilage in ,protobatrachus 7,fig4 #h7 can only be inferred1 and there are no median elements4 ,the agreement with ,ascaphus includes the presence1 in both1 of a separate coracoid ossification situated posterior to the ossified scapulocoracoid 7actually scapula74 ,this ossification is evidently that shown in ,notobatrachus as coracoid4 ,direct comparison of the three genera with one another suggests that if we use the term arciferal for any1 we should use it for all4 ,in the remote predecessor of ,anura1 ,amphibamus of the ,pennsylvanian1 the pectoral girdle was less substantial than in many of its contemporaries1 but it contained the primitive median interclavicle in addition to the clavicle1 cleithrum1 and scapulocoracoid4 7,the figure of ,watson1 #aidj1 and that by ,gregory1 #aiej1 are of individuals of different ages1 the latter being older47 ,it is clear that the paired elements of such a girdle were held rigid by their attachment to the interclavicle1 via the clavicles4 ,subsequent elimination of the interclavicle in the ,anuran line of descent1 and decrease of ossification1 left a girdle like that of ,protobatrachus1 ,notobatrachus1 ,ascaphus and ,leiopelma4 ,but in several advanced families a more rigid median sternum1 of one or two bony pieces plus cartilage1 is developed secondarily1 possibly 7as ,cope1 #ahhi3 #bdg1 suggested7 in correlation with axillary amplexus4 ,among ,urodela no dermal bones occur in the pectoral girdle4 ,there is usually a scapulocoracoid ossified as a single piece1 from which a thin cartilaginous suprascapula extends dorsally and a broad cartilaginous coracoid plate extends medially1 overlapping the one from the opposite side2 a precoracoid lobe of this reaches forward on either side1 and a median1 posterior sternum of cartilage may make contact with the edges of the two coracoids4 ,in ,siren and ,amphiuma two centers of ossification are found for each scapulocoracoid1 and in ,triton and ,salamandra three4 ,probably the more dorsal and lateral of these represents the primitive scapula and the other one 7or two7 the primitive coracoid4 ,comparing the girdle of a salamander with that of a frog1 the closest similarity can be seen between ,ascaphus and a salamander in which the scapula and coracoid ossify separately4 ,both have the median sternum in contact with the coracoid plates4 ,the major difference1 of course1 is the lack of clavicle and cleithrum in the salamander4 ,,carpus ,,and ,,tarsus ,in ,ascaphus 7,ritland1 #aiee;a2 cleared and stained specimens of nearly grown males7 distal carpals #a1 #b1 #c and #d are present and separate1 increasing in size in the order given 7,fig4 #i74 ,a prepollex rests against centrale #a2 centralia #b and #c are fused2 the radiale fuses with centrale #d1 and the intermedium fuses with the ulnare2 radius and ulna are fused with each other as in other frogs4 ,the digits 7and metacarpals7 are considered by ,ritland to be #a-d1 in addition to the prepollex1 rather than #b-e4 ,illustration3 ,fig4 #i4 ,skeleton of fore foot of ,notobatrachus 7after ,stipanicic and ,reig1 #aief1 terminology revised7 and ,ascaphus 7after ,ritland1 #aiee a72 all x#e4 ,for explanation of abbreviations see ,fig4 #c4 ,in the ,jurassic ,notobatrachus ,stipanicic and ,reig 7#aief7 have shown the carpus with surprising clarity 7,fig4 #i74 ,if their nomenclature of the parts be revised1 we obtain a fairly close resemblance to ,ascaphus1 except that centralia #b and #c are not fused1 distal carpals #a and #b do not show 7which would easily be understood if they were of the size of those in ,ascaphus1 or not ossified71 and the intermedium remains separate from the ulnare4 ,in ,salamandra 7,francis1 #aicd2 ,nauck1 #aich7 distal carpals #a and #b are fused in both larva and adult1 and #c and #d are separate2 the radiale1 intermedium and ulnare are separate in the larva but the latter two fuse in the adult2 centrale #a 7labelled prepollical cartilage by ,francis7 and centrale #b are separate4 ,francis considers the digits 7and metacarpals7 to be #a-d4 ,apparently the arrangement here indicated for the larva is characteristic of other larval salamanders1 except where further reduced1 and reduction below the number given for the adult is common in other terrestrial forms4 ,the radius and ulna are1 of course1 separate4 ,the ossification of carpals is more likely to be complete in adult frogs than in salamanders1 but some ossification of all parts named is found in several of the latter4 ,a common ancestor of frogs and salamanders could be expected to have the following elements present and ossified in the adult3 distal carpals #a-d separate2 #c centralia2 radiale1 intermedium and ulnare separate4 ,comparison with fossils older than ,notobatrachus is fruitless on these points1 unless we go back to forms too distant to have any special value1 such as ,eryops4 ,this is because of inadequate preservation and because the elements are not fully ossified in many immature specimens4 ,for the purpose of this review there is no special value in a comparison of the tarsi of frogs and salamanders1 since the leaping adaptation of the former leaves very little common pattern between them4 ,even in ,protobatrachus1 where the legs were not yet conspicuously lengthened1 the tibiale and fibulare 7astragalus and calcaneum respectively7 were already considerably elongated4 ,the carpus and tarsus of ,amphibamus are as yet undecipherable4 ,,the ,,larva ,considering the postembryonic developmental stages of modern ,amphibia1 there can be no doubt that a gill-bearing1 four-legged larva of a salamander1 in which lateral line pores and a gular fold are present1 represents much more closely the type of larva found in labyrinthodonts than does the limbless1 plant-nibbling tadpole of the ,anura4 ,salamander-like larvae of labyrinthodonts are well known1 especially those formerly supposed to comprise the order ,branchiosauria4 ,many1 perhaps the majority of1 labyrinthodonts show some features associated with aquatic life even when full-grown1 as do the lepospondyls4 ,these features may include impressions of sensory canals on the dermal bones of the skull1 persistence of visceral arches1 reduction in size of appendages1 and failure of tarsal and carpal elements to ossify4 ,in fact1 it appears that very few of the ,paleozoic ,amphibia were successful in establishing themselves as terrestrial animals even as adults4 ,nevertheless1 in the ancestry of ,anura1 and that of at least the ,hynobiid1 ,ambystomid1 ,salamandrid and ,plethodontid salamanders1 there must certainly have been a terrestrial adult1 transforming from an aquatic larva4 ,the leaping mechanism of ,anura1 shown in so many features of their anatomy1 is perhaps to be explained as a device for sudden escape from land into the water1 but it was not yet perfected in the ,triassic ,protobatrachus or the ,jurassic ,notobatrachus4 ,the middle ear1 its sound-transmitting mechanism1 and the tympanum1 well developed in most ,anura1 are readily derived from those of early labyrinthodonts1 and are presumably effective for hearing airborne sounds whether on land or while floating in the water4 ,reduction of these organs in ,urodela may be correlated with their customary restriction to subsurface habitats and inability to maintain a floating position while in water4 ,some light may be shed on the significance of the tadpole of ,anura by considering the early stages of the ribbed frogs1 ,liopelmidae4 ,leiopelma and ,ascaphus are so closely similar in the adult that there is no doubt that they belong in one family1 primitive in some respects 7including articulated ribs2 pyriformis and caudalipuboischiotibialis muscles7 but not in others 7absence of tympanum and middle ear74 ,in both genera the eggs are large1 #e mm4 in ,leiopelma1 #d4e mm4 in ,ascaphus1 and unpigmented2 but at this point the resemblance ends4 ,illustration3 ,fig4 #aj4 ,leiopelma hochstetteri larva1 lateral and ventral 7after ,stephenson1 #aiee71 x#d4 ,stephenson 7#aiee7 showed that embryos of ,l4 hochstetteri develop equally well on land 7in damp places7 or in the water1 and that embryos prematurely released from egg capsules develop successfully in the water4 ,the larvae possess both pairs of legs 7,fig4 #aj7 and a broad gular fold similar to that of larval salamanders4 ,in ,l4 hochstetteri the fold grows back over the forelegs temporarily1 but remains free from the body and presently the legs reappear1 whereas in ,l4 archeyi the forelegs are not covered at any time4 ,no branchial chamber or spiracle is formed4 ,of course direct development1 without a tadpole1 occurs in several other groups of ,anura1 but in each case terrestrial adaptations are obvious4 ,this is not true of ,leiopelma1 which ,stephenson regards as more nearly comparable with ,urodela in its development than with other ,anura1 and he sees in it a primary and amphibious mode instead of a terrestrial specialization4 ,the ,ascaphus tadpole bears no outward resemblance to the larva of ,leiopelma1 but is a normal tadpole in form1 although sluggish in activity4 ,its greatly expanded labial folds bear numerous rows of horny epidermal teeth1 which1 with the lips1 serve to anchor the tadpole to stones in the swift water of mountain brooks4 ,noble 7#aibg7 noticed that particles of food were taken in through the external nares1 and that a current of water passed through these openings and out by way of the median spiracle4 ,it appears that any action by the teeth and jaws in scraping algae from the rocks 7which were bare in the stream where ,i have collected ,ascaphus7 would be quite incidental1 and that the lips and teeth must be primarily a clinging mechanism4 ,certain other mountain brook tadpoles 7for example1 ,borborocoetes7 show similar devices1 but these are developed independently1 as specializations from the usual sort of tadpole4 ,may it not be that closure of the gill-chamber by the opercular 7gular7 fold1 retardation of limb development1 expansion of the lips1 growth of parallel rows of horny teeth1 and other correlated features that make a tadpole1 were brought about as an adaptation of the primitive ,anuran larva to a swift-stream habitat1 and that this basic patent then later served to admit the tadpoles of descendant types to an alga-scraping habit in quiet water as well8 ,the tadpole1 as a unique larval type among vertebrates1 bears the hallmarks of an abrupt adaptive shift1 such as might have occurred within the limits of a single family1 and it seems difficult to imagine the enclosed branchial chamber1 the tooth-rows1 and lips of a familiar tadpole as having evolved without some kind of suctorial function along the way4 ,,summary ,the ,anura probably originated among temnospondylous labyrinthodonts1 through a line represented approximately by ,eugyrinus1 ,amphibamus1 and the ,triassic frog ,protobatrachus1 as shown by ,watson1 ,piveteau and others4 ,the known ,paleozoic lepospondyls do not show clear indications of a relationship with ,urodela1 but ,lysorophus may well be on the ancestral stem of the ,apoda4 ,between ,urodela and ,anura there are numerous resemblances which seem to indicate direct relationship through a common stock3 7#a7 a similar reduction of dermal bones of the skull and expansion of palatal vacuities2 7#b7 movable basipterygoid articulation in primitive members of both orders2 7#c7 an operculum formed in the otic capsule1 with opercularis muscle2 7#d7 many details of cranial development1 cranial muscles1 and thigh muscles1 especially between ,ascaphus and the ,urodela1 as shown by ,pusey and ,noble2 7#e7 essentially similar manner of vertebral development1 quite consistent with derivation of both orders from ,temnospondyli2 7#f7 presence in the larva of ,leiopelma of a salamander-like gular fold1 four limbs1 and no suggestion of modification from a tadpole 7,stephenson74 ,,literature ,,cited ,broom1 ,r4 #aiah4 ,observations on the genus ,lysorophus ,cope4 ,ann4 ,mag4 ,nat4 ,hist41 7#i7b3bcb-bci4 ,bystrow1 ,a4 ,p4 #aich4 ,dvinosaurus als neotenische ,form der ,stegocephalen4 ,acta ,zool41 #ai3bji-bie4 ,case1 ,e4 ,c4 #aice4 ,description of a collection of associated skeletons of ,trimerorhachis4 ,contrib4 ,mus4 ,pal4 ,univ4 ,michigan1 #d3bbg-bgd4 ,cope1 ,e4 ,d4 #ahhi4 ,the ,batrachia of ,north ,america4 ,bull4 ,u4 ,s4 ,nat4 ,mus41 #cd3a-ebe4 de ,beer1 ,g4 ,r4 #aicg4 ,the development of the vertebrate skull4 ,pp4 xxiii #eeb4 ,oxford1 ,clarendon ,press4 de ,villiers1 ,c4 ,g4 ,s4 #aicd4 ,studies of the cranial anatomy of ,ascaphus truei ,stejneger1 the ,american ,liopelmid4 ,bull4 ,mus4 ,comp4 ,zool41 #gg3a-ch4 ,emelianov1 ,s4 ,w4 #aicf4 ,die ,morphologie der ,tetrapodenrippen4 ,zool4 ,jahrb4 7,anat471 #fb3agc-bgd4 ,francis1 ,e4 ,t4 ,b4 #aicd4 ,the anatomy of the salamander4 ,pp4 xxxi #cha4 ,oxford1 ,clarendon ,press4 ,gamble1 ,d4 ,l4 #aibb4 ,the morphology of the ribs and the transverse processes of ,necturus maculatus4 ,jour4 ,morph41 #cf3ecg-eff4 ,gray1 ,p4 #aicj4 ,on the attachments of the ,urodele rib to the vertebra and their homologies with the capitulum and tuberculum of the ,amniote rib4 ,proc4 ,zool4 ,soc4 ,london1 #aicj7aica73ijg-iaa4 ,gregory1 ,j4 ,t4 #aiej4 ,tetrapods from the ,pennsylvanian nodules from ,mazon ,creek1 ,illinois4 ,am4 ,jour4 ,sci41 #bdh3hcc-hgc4 ,hecht1 ,m4 ,e4 #aieg4 ,a case of parallel evolution in salamanders4 ,proc4 ,zool4 ,soc4 ,calcutta1 ,mookerjee ,mem43#bhc-bib4 ,holmgren1 ,n4 #aicc4 ,on the origin of the tetrapod limb4 ,acta ,zool41 #ad3ahe-bie4 #aici4 ,contributions to the question of the origin of the tetrapod limb4 ,acta ,zool41 #bj3hi-abd4 #aidi;a4 ,contributions to the question of the origin of tetrapods4 ,acta ,zool41 #cj3dei-dhd4 #aidi;b4 ,on the tetrapod limb problem again4 ,acta ,zool41 #cj3dhe-ejh4 ,herre1 ,w4 #aice4 ,die ,schwanzlurche der mitteleocaenen 7oberlutetischen7 ,braunkohle des ,geiseltales und die ,phylogenie der ,urodelen unter ,einschluss der fossilen ,formen4 ,zoologica1 #cc3hg1 #a-e4 ,jarvik1 ,e4 #aidb4 ,on the structure of the snout of ,crossopterygians and lower gnathostomes in general4 ,zool4 ,bidrag fran ,upsala1 #ba3bce-fge4 #aieb4 ,on the fish-like tail in the ,ichthyostegid ,stegocephalians4 ,meddelelser on ,gronland1 #aad7ab73a-ij4 ,mookerjee1 ,h4,k4 #aicj;a4 ,on the development of the vertebral column of the ,urodela4 ,phil4 ,trans4 ,roy4 ,soc4 ,london1 ,b #bah3dae-ddf4 #aicj;b4 ,on the development of the vertebral column of the ,anura4 ,philos4 ,trans4 ,royal ,soc4 ,london1 ,b #bai3afe-aif4 ,mac,bride1 ,e4,w4 #aicb4 ,recent work on the development of the vertebral column4 ,cambridge1 ,biol4 ,rev41 #g3ajh-adh4 ,mc,dowell1 ,s4,b4 #aieh4 ,are the frogs specialized seymouriamorphs8 7,abstract7 ,anat4 ,rec41 #acb7c73dgb4 ,naef1 ,a4 #aibi4 ,notizen zur ,morphologie und ,stammesgeschichte der ,wirbeltiere4 #ae4 ,dreissig ,thesen ueber ,wirbelsaeule und ,rippen1 insbesondere bei den ,tetrapoden4 ,zool4 ,jahrb41 #ej3eha-fjj4 ,noble1 ,g4 ,k4 #aibb4 ,the phylogeny of the ,salientia2 ,i4 ,the osteology and the thigh musculature2 their bearing on classification and phylogeny4 ,bull4 ,amer4 ,mus4 ,nat4 ,hist41 #df3a-hg4 #aibg4 ,the value of life-history data in the study of the evolution of the ,amphibia4 ,annals ,new ,york ,acad4 ,sci41 #cj3ca-abh4 ,piveteau1 ,j4 #aicg4 ,un ,amphibien du ,trias inferieur4 ,essai sur l'origine et l'evolution des ,amphibiens ,anoures4 ,annales de ,paleontologie1 #bf3ace-agf4 #aiee4 ,anoura4 ,in3 ,traite de ,paleontologie1 #e3bej-bgd4 ,j4 ,piveteau1 ,masson et ,cie1 ,paris4 ,pusey1 ,h4 ,k4 #aidc4 ,on the head of the liopelmid frog1 ,ascaphus truei4 ,i4 ,the chondrocranium1 jaws1 arches1 and muscles of a partly grown larva4 ,quart4 ,jour4 ,micr4 ,sci41 #hd3aje-ahe4 ,reed1 ,h4 ,d4 #aiae4 ,the sound-transmitting apparatus in ,necturus4 ,anat4 ,rec41 #i3eha-eij4 ,remane1 ,a4 #aicf4 ,wirbelsaeule und ihre ,abkoemmlinge4 ,in3 ,handbuch der vergleichenden ,anatomie der ,wirbeltiere1 ,l4 ,bolk et al41 #d3a-bjf4 ,urban and ,schwarzenberg1 ,berlin1 ,vienna4 ,ritland1 ,r4 ,m4 #aiee;a4 ,studies on the post-cranial morphology of ,ascaphus truei4 ,i4 ,skeleton and spinal nerves4 ,jour4 ,morph41 #ig3aai-agd4 #aiee;b4 ,studies on the post-cranial morphology of ,ascaphus truei4 ,,ii4 ,myology4 ,jour4 ,morph41 #ig3bae-bhb4 ,romer1 ,a4 ,s4 #aide4 ,vertebrate paleontology4 #bnd edition4 ,pp4 viii #fhg4 ,univ4 ,chicago ,press4 #aidg4 ,review of the ,labyrinthodontia4 ,bull4 ,mus4 ,comp4 ,zool41 #ii3c-cfh4 ,saeve-,soederbergh1 ,g4 #aicd4 ,some points of view concerning the evolution of the vertebrates and the classification of this group4 ,arkiv foer ,zoologi1 #bf;,a3#a-bj4 ,stadtmueller1 ,f4 #aicf4 ,kranium und ,visceralskelett der ,stegocephalen und ,amphibien4 ,in3 ,handbuch der vergleichenden ,anatomie der ,wirbeltiere1 by ,l4 ,bolk et al41 #d3eja-fih4 ,stephenson1 ,n4 ,g4 #aiee4 ,on the development of the frog1 ,leiopelma hochstetteri ,fitzinger4 ,proc4 ,zool4 ,soc4 ,london1 #abd7d73ghe-gie4 ,stipanicic1 ,p4 ,n4 and ,reig1 ,o4 ,a4 #aiee4 ,breve noticia sobre el hallazgo de anuros en el denominado ,complejo ,porfirico de la ,patagonia ,extraandina1 con consideraciones acerca de la composicion geologica del mismo4 ,revista de la ,asoc4 ,geol4 ,argentina1 #aj7d73bae-bcc4 #aief4 ,el complejo porfirico de la ,patagonia extraandina y su fauna de ,anuros4 ,acta ,geol4 ,lilloana 7,univ4 ,nac4 del ,tucuman71 #a3ahe-big4 ,sushkin1 ,p4 ,p4 #aicf4 ,notes on the pro-,jurassic ,tetrapoda from ,u4 ,s4 ,s4 ,r4 ,,iii4 ,dvinosaurus ,amalitzky1 a perennibranchiate stegocephalian from the ,upper ,permian of ,north ,dvina4 ,trav4 ,inst4 ,pal4 ,acad4 ,sci4 ,,urss1 #e3dc-ia4 ,watson1 ,d4 ,m4 ,s4 #aidj4 ,the origin of frogs4 ,trans4 ,roy4 ,soc4 ,edinburgh1 #dj7g73aie-bca4 ,transmitted ,april #g1 #aiei4