A PHYLOGENY AND CLASSIFICATION OF THE HIGHER CATEGORIES OF

EUGENE S. GAFFNEY

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EUGENE S. GAFFNEY Assistant Curator, Department of Paleontology The American Museum of Natural History Adjunct Professor, Department of Geological Sciences Columbia University

BULLETIN OF THE AMERICAN MUSEUM OF NATURAL HISTORY VOLUME 155: ALRTICLE 5 NEW YORK: 1975 BULLETIN OF THE AMERICAN MUSEUM OF NATURAL HISTORY Volume 155, article 5, pages 387-436, figures 1-27, tables 1-5

Issued July 24, 1975 Price. $2.40

ISSN 0003-0090

This article completes Volume 155.

Copyright © The American Museum of Natural History 1975 C O N T E N T S

Abstract . 391 Introduction. 391 Comparison of the Head in Living Cryptodires and Pleurodires . 392 The Jaw Mechanism . 392

The Palatoquadrate Region ...... 394 Other Cranial Features . 401 Historical Review of the Amphichelydian Concept . 402 The Baenoidea Compared with and ...... 407 Skull Characters. 407 Postcranial Characters. 411 The and Eucryptodira. 416 Relationships within the Eucryptodira . 416 Superfamily Trionychoidea. 416 Superfamily Chelonioidea . 417 Superfamily 420 The Early History of Turtles 420 Classification. 422 Summary. 430 Literature Cited. 433

389

ABSTRACT Shared derived characters of the basicranium that the trochlea evolved independently in provide the basis for a new theory of relation- cryptodires and pleurodires. Cranial arteries and ships and a new classification of the major groups the canals and foramina associated with them of living and extinct turtles. Post- turtles provide characters used to develop hypotheses of are characterized by a jaw-closing mechanism relationship among the Cryptodira. where the main adductor tendon rides over a The taxon "Amphichelydia," characterized trochlea, a condition unique among . by primitive features and supposedly containing A study of the trochlear mechanism and associ- the ancestors of Recent turtles, is rejected and its ated basicranial adaptations for akinesis suggests members distributed to monophyletic taxa.

I N T R O D U C T I O N Matthew (1924, p. 210) said: "I venture to cor, coronoid pm, premaxilla remark that a more careful search for skulls of den, dentary po, postorbital extinct chelonians, and less reliance upon the epi, epipterygoid pr, prootic characters of the carapace and plastron might ex, exoccipital pra, prearticular the fr, frontal pt, pterygoid perhaps aid in clearing up real affinities of ju, jugal qj, quadratojugal both fossil and recent members of the . A mx, maxilla qu, quadrate classification of mammals based primarily upon na, nasal so, supraoccipital the number and relations of the ribs and taking op, opisthotic sq, squamosal no serious account of the skull would probably pa, parietal sur, surangular be as unsatisfactory as are the current classifi- pal, palatine vo, vomer cations of fossil chelonians." pf, prefrontal The purpose of the present paper is to take Matthew's advice and develop a hypothesis of Institutional Abbreviations relationships among the turtles using characters AMNH, Department of Vertebrate Paleontology, obtained, for the most part, from the skull. the American Museum of Natural History Cranial features of turtles have been infrequently AMNH (H.), Department of Herpetology, the used for phylogenetic purposes, yet the potential American Museum of Natural History of the skull as a source of characters has been MCZ, Museum of Comparative Zoology, Harvard known for some time (e.g., Siebenrock, 1897). In University addition, much of the known diversity of extinct UT, Slide collection of Dr. Thomas Parsons, turtles is represented by cranial material, and this Department of Zoology, University of To- adds an important perspective to studies of ronto Recent forms. YPM, Yale Peabody Museum, Yale University I summarize here information from a larger, but as yet unpublished, work on skull METHODOLOGY morphology (Gaffney, MS). More detailed Recent years have witnessed a renewed in- descriptions and other figures will be found terest in self-examination by systematists. The there. The terminology I use is from a figured primary concern in this endeavor involves the glossary (Gaffney, 1972b). philosophic formulation of methodology for the purpose of increasing rigor and objectivity. The Anatomical Abbreviations works of Popper (1968a, 1968b, 1972) have Used in influenced some systematists (e.g., Ghiselin, Figures 2-5, 7, 9-19, 23 1969; Bock, 1973), and his characterization of ang, angular bo, basioccipital science as a series of refutable but not con- art, articular bs, basisphenoid firmable hypotheses has considerable merit as a 391 392 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 155 basis for discussion. Any method of determining has been termed the Bodenaponeurosis by Lakjer relationships (i.e., phylogeny reconstruction in (1926) and the Adduktorensehne by Schumacher the strict sense) should be expressed in the con- (1954) and others. In most this main text of a testable hypothesis. Although there is adductor tendon or Bodenaponeurosis attaches no unanimity as to what particular method is on or near the coronoid process (in mammals the most compatible with Popper's ideas, Hennig's coronoid process is essentially an ossified phylogenetic systematics or cladism (1966) Bodenaponeurosis; see Frazzetta, 1968) and ex- seems to me most fruitful. In any case it is impor- tends posterodorsally into the temporal region. tant to explain the methods used in a study so The greater part of the adductor jaw muscle that other workers will be able to test the hy- fibers extend from bones within the temporal potheses presented using different methods. region to attach onto the Bodenaponeurosis A number of reviews concern the use of (Frazzetta, 1968, fig. 2). Contraction of these shared derived characters in phylogeny recon- fibers pulls the Bodenaponeurosis or main ad- struction and provide extensive discussion: Hen- ductor tendon posterodorsally into the skull and nig, 1966; Brundin, 1966, 1968; Schaeffer, adducts the lower jaw. Recent turtles, as opposed Hecht, and Eldredge, 1972. Briefly, a cladistic to all other tetrapods, have a main adductor ten- phylogeny attempts to express the genealogic don that rides over a pulley or trochlea and relations of taxa in the strict sense without changes its direction of movement within the indicating the degree of morphologic similarity skull (fig. 1). This tendon in turtles contains a or difference (except for shared derived char- cartilage, the cartilago transiliens of Schumacher acters that may be considered similarities). (1956, figs. 3-5), which is developed where the Relationship means relative recency of common tendon passes over the trochlea. The cartilago ancestry, that is, two taxa are more closely transiliens is roughly meniscus-shaped with the related to each other than to a third taxon if the concavity fitting the trochlea. first two share an ancestor that the third does This trochlear system seems to be related to not. Recency of common ancestry is determined the enlargement of the otic chamber in turtles by shared derived characters, characters that are that fills much of the area containing jaw muscu- assumed to have evolved in the common ancestor lature in other . This expanded otic region of two taxa and to have been inherited by them. would interfere with the Bodenaponeurosis of a As with other methods of phylogeny recon- "typical" if the trochlea were absent. The struction the identification of homologous char- mechanism in turtles results in a reorientation of acters and the recognition of parallelism is still a the main adductor musculature and has interest- fundamental problem. ing consequences for the structure of the che- lonian temporal region. Expansion of the muscle COMPARISON OF THE HEAD IN LIVING attachment area extends posteriorly in turtles, CRYPTODIRES AND PLEURODIRES along an unusually well-developed sagittal crest and post-temporal fenestra, rather than postero- The jaw mechanism. Schumacher (1954, dorsally, as in most tetrapods. 1955a, 1955b, 1956) has described the jaw All living turtles possess this trochlear mecha- musculature of turtles in an excellent series of nism but a detailed examination of its morphol- monographs. He demonstrated that living turtles ogy reveals that the trochlear apparatus is con- have a trochlear apparatus that is unique among structed differently in cryptodires and pleuro- vertebrate jaw-closing systems. Most tetrapods dires (Schumacher, 1956). In cryptodires the have the adductor jaw musculature arranged in a cartilago transiliens is found in a true joint, with pinnate manner around one or more tendinous synovial cavity and underlying cartilage, that is sheets (Lakjer, 1926; Edgeworth, 1935; Fraz- formed on the anterodorsal margin of the otic zetta, 1968). There is usually one pinnate ten- chamber, the processus trochlearis oticum (figs. don-muscle system that is the primary lower jaw 1, 2). The processus (Gaffney, 1972b) is usually adductor or at least the largest in the head, and it formed by the quadrate or prootic or both. In 1975 GAFFNEY: TURTLE PHYLOGENY 393

A

B

C processus trochlearis pterygoidei FIG. 1. A comparison of the external adductor tendon in nonchelonian reptiles (A), cryptodiran turtles (B), and pleurodiran turtles (C). Size and shape of structures are indicated diagrammatically. pleurodires a different bony element, a postero- trochlea differs with respect to the M. adductor lateral process of the pterygoid, the processus mandibulae internus musculature as indicated by trochlearis pterygoidei (ibid.) bears the cartilago Schumacher (see especially 1954, pls. 11 and transiliens of the main adductor tendon or 12). In pleurodires the trochlea is anterior to this Bodenaponeurosis (figs. 1, 3). Although the musculature, whereas in cryptodires the trochlea trochlea consists of a true joint with synovial is posterior to it. capsule in cryptodires, it is morphologically very These features, summarized below, strongly different in pleurodires. The cartilago transiliens suggest that the trochlear apparatus of crypto- has the same shape, but instead of a synovial dires, as a trochlear mechanism, is not homolo- capsule the "joint" is formed by an infolding of gous to that of pleurodires. the mucous membrane of the mouth (the 1. The bony elements supporting the trochlea ductus angularis oris of Schwartz, 1934, fig. 9) in are nonhomologous, i.e., the pterygoid in pleuro- pleurodires (fig. 13). Also, the position of the dires and the quadrate-prootic in cryptodires. 394 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 155

fenestra ovalis canalis cavernosus FIG. 2. serpentina, AMNH (H.) 9249. Lateral view of a cryptodire skull with a parasagittal section on right side removed to show ethmoid region and processus trochlearis oticum. Hatching indicates cut surfaces; compare with figure 3 (see also Gaffney, 1972b, figs. 5, 6).

2. The morphology of the joint capsules are The palatoquadrate region. Cryptodires and nonhomologous, i.e., a synovial joint in crypto- pleurodires have distinct differences in the rela- dires and folded oral mucosa in pleurodires. tive proportions and positions of the bones mak- 3. The trochlea is in a different morphologic ing up the basicranium. Pleurodires have a medial position with respect to the M. adductor mandib- process of the quadrate that forms the main ulae internus jaw musculature. brace to the braincase, whereas in cryptodires the At the present time I contend that neither jaw pterygoid extends posteriorly to form the brace mechanism type is primitive with respect to the between braincase and quadrate (figs. 10, 11, 18, other but that both are derived and, therefore, 19). The cavum acustico-jugulare is covered are important characters for demonstrating the ventrally (in part) by this posterior extension of strictly monophyletic nature of the Cryptodira the pterygoid in cryptodires but in pleurodires and Pleurodira (as here conceived). this area is not floored by the pterygoid. These 1975 GAFFNEY: TURTLE PHYLOGENY 395

fenestra ovalis FIG. 3. sp., AMNH (H.) 72418. Lateral view of a pleurodire skull with a parasagittal section on right side removed to show ethmoid region and processus trochlearis pterygoidei. Latter structure projects lateral to the plane of the section. Hatching indicates cut surfaces. Compare with figure 2. differences are related to a more general condi- and DeBeer (1937). A relatively generalized con- tion which involves the morphology of the dition of this area can be seen in primitive rep- palatoquadrate, neurocranium, and the inter- tiles, such as Captorhinus (Romer, 1956, fig. 36). vening area, the cranioquadrate space. In these forms, the palatoquadrate is articulated The cranioquadrate passage or space, the ele- to the braincase solely by means of the basiptery- ments of the palatoquadrate, and the primary goid articulation, and the skull is usually con- neurocranium are described and discussed by sidered to be kinetic (Goodrich, 1930; Bock, Goodrich (1930, see especially figs. 339, 493) 1964). In Recent turtles, the basipterygoid 396 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 155

) .:

:, .-

foramen anterius canalis carotici interni FIG. 4. Chelydra serpentina, AMNH (H.) 107387. Lateral view of primary neurocranium in a cryptodire. Hatching indicates sutural contact with palatoquadrate elements above remnants of cranio-quadrate space. Anterior is at left. See figure 5. articulation is fused and the area of the cranio- sutural contact of the braincase (prootic, quadrate space is nearly obliterated by the broad opisthotic) and palatoquadrate (quadrate, ptery- 1975 GAFFNEY: TURTLE PHYLOGENY 397

llateral head vein

es sus interfenestralis bs/ f oa rostrum basisphenoidale VII hyomandibular foramen anterius canalis carotici interni foramen posterius canalis carotici interni canalis caroticus internus FIG. 5. Emydura cf. australis, AMNH (H.) 108957. Lateral view of primary neurocranium in a pleurodire. Hatching indicates sutural contact with palatoquadrate elements above remnants of cranio-quadrate space. Anterior is at left. See figure 4. goid). The akinetic conditions of turtles, then, to the articulation. It is the nature of these sub- not only include fusion of the basipterygoid sidiary contacts that suggests ideas concerning articulation but also the development of these the early history of turtles, because the way in subsidiary contacts anterior, dorsal, and posterior which the fusion has taken place is different in 398 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 155

'AV A

FIG. 6. Chelydra serpentina, AMNH (H.) 107387. Ventral view of pri- mary neurocranium in a cryptodire (cf. figs. 8, 9). Anterior is toward top of page.

cryptodires and pleurodires (I am indebted to of the contact. However, anterior and ventral to S. B. McDowell, who first suggested this notion). the stapedial artery (contained in the canalis I begin an analysis of this region posteriorly, stapedio-temporalis) there are consistent dif- using the processus paroccipitalis of the opis- ferences. The most obvious one has already been thotic as a reference point. The sutural contact mentioned above, the quadrate versus pterygoid of the processus paroccipitalis to the posterior bracing of the palatoquadrate elements. This dif- portion of the quadrate seems to be the same in ference is also correlated with differences in the both cryptodires and pleurodires as there are no structures that run through the remnants of the consistent morphologic differences in the nature cranioquadrate space. In all cryptodires the 1975 GAFFNEY: TURTLE PHYLOGENY 399

A canalis caroticus lal inervi trigemini

foramen anterius canalis carotici interni - canalis caroticus internus- ._

cavum labyrinthicum b

Ihead vein

ll

FIG. 7. Chelydra serpentina, AlMNH (H.) 107387. Key to figure 6. lateral head vein (vena capitis lateralis) and the the skull rather than outside as in pleurodires and hyomandibular branch of the facial (VII) nerve usually exits from the foramen nervi trigemini. (proximal to the origin of the chorda tympani) Although in some cryptodires (the superfamily run together in the canalis cavernosus, whereas in Trionychoidea of this author) the stapedial pleurodires the nerve is more or less separated artery is reduced or absent and the mandibular from the lateral head vein by bone, and there- artery comes off some other artery inside the fore, lies outside the canalis cavernosus. The skull (usually the palatine or internal carotid) the mandibular artery of pleurodires branches from mandibular artery still exits via the foramen nervi the stapedial artery after the latter leaves the trigemini (in Caretta and some the skull via the foramen stapedio-temporale. The mandibular artery is partitioned off from the mandibular artery of most cryptodires (fig. 14), other structures due to subdivision of the however, branches off the stapedial artery inside foramen nervi trigemini). Most cryptodires, 400 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 155

FIG. 8. Emydura cf. australis, AMNH (H.) 108957. Ventral view of primary neurocranium in a pleurodire (cf. figs. 6, 7). Anterior is toward top of page. therefore, have the mandibular artery traversing extension of the quadrate in , and the canalis cavernosus (even in Caretta and Geo- the lateral bracing of the pterygoid in Chelydra. chelone), whereas pleurodires do not have the Most cryptodires have an epipterygoid bone mandibular artery in the canalis cavernosus and it but all pleurodires lack this element (figs. 2, 3). does not exit via the trigeminal foramen. The pleurodire condition may be the result of These differences can be seen in transverse the absence or extreme reduction of the carti- sections through the canalis cavernosus (figs. laginous precursor of the epipterygoid in that 10-17). For example, the canalis cavernosus of group. Dermochelys, a cryptodire lacking an the cryptodire Chelydra contains the hyoman- epipterygoid, does have the cartilaginous pre- dibular nerve, the mandibular artery, and the cursor of that bone but ossification does not take lateral head vein. The canalis cavernosus in the place (DeBeer, 1937, p. 261). Although Fuchs pleurodire Podocnemis, however, contains only (1932) and Schwartz (1934) illustrated a few the lateral head vein, with the hyomandibular cross sections of an embryonic Podocnemis head, nerve separated by bone and the mandibular the embryology of a pleurodire cranium has artery absent. The sections also show the medial never been described, therefore meaningful com- 1975 GAFFNEY: TURTLE PHYLOGENY 401

-foramen nervi.facialis

; interfenestralis

-processus paroccipitalis

FIG. 9. Emydura cf. australis, AMNH (H.) 108957. Key to figure 8. parisons cannot be made at the present time. Although the foramen palatinum posterius of Nonetheless, the absence of an epipterygoid in turtles appears to be homologous to the palatine pleurodires does heighten the distinction be- fenestra of other reptiles (Romer, 1956, p. 71), I tween the palatoquadrate elements of pleurodires have no idea which condition is primitive for and cryptodires. As is the case with the jaw turtles. mechanism, it seems likely that the cryptodire The foramen supramaxillare (Albrecht, 1967; and pleurodire palatoquadrate conditions are Gaffney, 1972b) is present in most cryptodires both derived with respect to each other and that but not in pleurodires (Albrecht, personal one did not give rise to the other. commun.). This foramen conducts an artery into Other cranial features. The position of the the nutrient canals of the maxilla. The signifi- foramen palatinum posterius (fig. 23) and its cance of its absence in pleurodires is not known, relations to the vidian canal differ in cryptodires and it does not appear to be correlated with the and pleurodires. Cryptodires have the foramen palatoquadrate elements. As this structure does palatinum posterius ventral or lateral to the orbit not seem to occur in other reptiles, its presence (except in cheloniids in which it is absent), (or absence) in turtles may be primitive or whereas in pleurodires it is behind the orbit. The derived. anterior exit of the vidian canal lies in or close to In most cryptodires (some trionychids are an the foramen palatinum posterius in cryptodires; exception) the prefrontals possess ventromedial pleurodires either lack the canal (cheliids) or the processes (commonly called descending proc- exit lies on the ventral surface of the pterygoid. esses) that form an anterior wall for the orbit, a 402 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 155

I cavum tympani

/-1,stapedial artery cavum labyrinthicum 11 ,canalis cavernosus -lateral head vein

- columella auris

qu

pt VII hyome internal carotid artery CHELYDRA

FIG. 10. Chelydra serpentina, UT Chely 68. Transverse section through ear region of a cryptodire. Quadrate stippled. Skull midline on left. See figure 11. posterior wall for the fossa nasalis, and an articu- In 1884, Dollo (p. 75) suggested that some of lation with the vomer. Pleurodires lack the the turtles belong to a group, the "Tha- descending processes and have a fossa nasalis that lassemydes," which, he argued, was the common is largely or entirely open posteriorly. As with ancestor of all living turtles. He thought that the preceding character, I do not know its primi- these forms were neither cryptodires nor pleuro- tive or derived condition. dires but morphologically intermediate. A few years later, in 1889, Lydekker erected the HISTORICAL REVIEW OF THE "Amphichelydia" on a similar basis. In both AMPHICHELYDIAN CONCEPT cases the specimens involved were Jurassic and had plastra with paired indentations, sup- One of the more obvious novelties of the posedly sutures for the pubis, on the dorsal sur- classification proposed here is the absence of the face of the xiphiplastra. These indentations were Amphichelydia, a prominent higher category of supposed to represent an intermediate stage be- most turtle classifications. It seems appropriate tween the cryptodire condition with a free pelvis to include at this point a brief historical review and the pleurodire condition with both pubis and of this taxon. ischium sutured to the xiphiplastron. In fact, the 1975 GAFFNEY: TURTLE PHYLOGENY 403

I

I

k

cavum labyrinthicum

cavum tympani Istapedial artery k -canalis cavernosus VIl hyomandibular- lateral head vein columella auris

'qu @

internal carotid artery condJylus mandibularis PODOCNEMIS FIG. 1 1. Podocnemis expansa, UT POD III 211. Transverse section through ear region of a pleurodire. Quadrate stippled. Skull midline on left. See figure 10. indentations occur in most baenoids and appear of Cryptodira and Pleurodira. The quadrate to represent facets for a movable articulation resembles mostly that of the Pinnata [the living with the pelvis. Other evidence advanced by sea turtles], the whole arrangement of palate, Lydekker in support of the Amphichelydia was pterygoid, basisphenoid is that of Cryptodira, the the presence of mesoplastra and intergular scutes. presence of the epipterygoid is also a character of These elements are lost in many later turtles and the Cryptodira and so is the union of the appear to represent a primitive condition. descending processes of the prefrontal with the Baur (1891) described the first amphi- vomer. But the free nasals, the suturally united chelydian specimen with an associated skull, dentary bones, and the absence of the produc- () plicatulus (YPM 1357) tion of the petrosal are characteristic of the from the of Wyoming. He sup- Pleurodira" (1891, p. 414). Baur also compared ported the Amphichelydia as common ancestors the vertebrae of Glyptops with living turtles and of cryptodires and pleurodires and concluded as concluded that the cervicals of Glyptops were follows: "The skull as a whole shows characters closer to those of pleurodires than to cervicals of which we would expect to find in the ancestors cryptodires. 404 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 155

V2 external adductor tendon

Vil I superficial is

- pterygoideus

trachea

- .V<9 FIG. 12. Chelydra serpentina, UT Chely 49. Transverse section through anterior part of fossa temporalis in a cryptodire. This section is in about the same morphologic position as that in figure 13. Skull mid- line on left. Hay (1905) presented an extensive discussion shows, it seems to the writer, that where the of the Amphichelydia and the phylogeny of tur- characters are not primitive they are wholly, or tles. In this work, he utilized all aspects of the almost wholly, cryptodiran." Although Hay did morphology but stressed the shell. He criticized not diagnose the Amphichelydia in 1905, he did Baur's description of Glyptops, in particular so later (1908, pp. 43-44) when he said: "The- pointing out that Glyptops has no real pleuro- cophorous turtles having a carapace composed of diran characters (nasals are found in toxochelyid neural, costal, and peripheral bones and a plas- cryptodires but not in pelomedusid pleurodires, tron in which the epiplastra are in contact with the dentaries of Glyptops are fused, and some the hyoplastra. Mesoplastra usually, perhaps cryptodires have a processus trochlearis oticum always, present. Intergular and inframarginal as poorly developed as in Glyptops). Further- scutes probably always developed. Skull es- more, Hay (1905, p. 139) described some new sentially cryptodiran in structure, but with skull material of Amphichelydia that had been various primitive elements. Neck short, the verte- discovered recently: "An examination of the brae little differentiated. Limbs, so far as known, skulls of Compsemys (= Glyptops) and (= fitted for walking." Chisternon and Eubaena of Gaffney, 1972a) Hay's characterization relies entirely on the 1975 GAFFNEY: TURTLE PHYLOGENY 405

FIG. 13. Podocnemis expansa, UT POD III 149. Transverse sec- tion through anterior part of fossa temporalis in a pleurodire. This section is in about the same morphologic position as that in figure 12. Skull midline on left. postcranial elements, primarily on the presence In 1938 (pp. 251-252) Simpson summarized of mesoplastra and an intergular scute in the this concept of the Amphichelydia in a descrip- shell, and the absence of cervical vertebrae tion of the meiolaniid Crossochelys (, specializations. At the time, many Jurassic turtles Patagonia): "The Suborder Amphichelydia, to were being placed rather arbitrarily in either the which the , , and some Cryptodira or the Pleurodira. Apparently, Hay other ancient forms are now generally referred, is used the Amphichelydia as a taxonomically an essentially horizontal division for a divergent "practical" solution to the problem of deter- group of early phyla, mostly Mesozoic, which are mining the phylogeny of many forms that were distinguished from later forms and united with too far removed from living groups to be identi- each other by primitive characters. A strictly fied adequately. The evidence of the skull phyletic classification, were such possible, would morphology was ignored in favor of the post- reject this suborder as generally defined, but, as cranial evidence, but, at the time, the systematics so often happens in practical , it is now of turtles was based almost entirely on the post- most convenient if not necessary to recognize cranial morphology. it." 406 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 155

geniculate ganglion VII

FIG. 14. Chelydra serpentina, UT Chely 65. Transverse section through fossa acustico-facialis in a cryptodire. This section is in about the same morphologic position as that in figure 15. Skull midline on left. Romer (1956, pp. 497-498) also recognized very primitive Triassic types; the pleurosternoids, the horizontal nature of the Amphichelydia but typical amphichelydians; and baenoids, advanced he emphasized the supposed intermediate posi- forms." tion of the group, that is, as common ancestors Parsons and Williams (1961) presented a of the Cryptodira and Pleurodira: "A third major detailed morphologic study of two Jurassic group, the Amphichelydia, is essentially a Meso- amphichelydian skulls with a review of the origin zoic one, comprising primitive forms ancestral to of turtles based on an examination of the Triassic both the living suborders. ... This suborder was specimens from Germany. They concluded that erected to contain the older and more primitive the Jurassic skulls were "modern" in the sense turtles, almost entirely Mesozoic in age, which that they give no indication of the early stages of lack the distinctive features of either cryptodires the evolution of the turtle skull from nonche- or pleurodires. Certain of them are transitional in lonian ancestors. Their re-examination of the structure to these advanced groups, and the Triassic turtle, , demonstrated that group boundaries have varied from author to this form was much more primitive than any author. They are here arranged, in superfamilies, other known turtle and suggested that it be in three successive stages: the proganochelyoids, separated from all other turtles (ibid., p. 92). 1975 GAFFNEY: TURTLE PHYLOGENY 407

adductor mandibulae externus pars profundus

processus inferior parietalis-

FIG. 15. Podocnemis expansa, UT POD III 201. Transverse section through fossa acustico-facialis in a pleurodire. This section is in about the same morphologic position as that in figure 14. Skull midline on left.

This suggestion was followed by Romer (1966, p. phologic criteria usually thought to represent 365) to the extent that he elevated the Triassic primitive character states. to the subordinal level and recognized the Suborders Proganochelydia, Amphichelydia, Cryptodira, and Pleurodira. In Romer's classifi- THE BAENOIDEA COMPARED WITH cation the Triassic turtles are excluded from the CRYPTODIRA AND PLEURODIRA Amphichelydia but in another recent classifi- Skull Characters. Table 3 summarizes the cri- cation (Zangerl, 1969) the Amphichelydia con- teria most useful in differentiating living crypto- sists primarily of the Triassic forms. In fact, there dires and pleurodires. Each of these are discussed is only one common to the Amphichelydia in relation to baenoids. of Romer and Zangerl. Although a consensus 1. One of the main osteologic indications of hardly exists, it would seem that most authors the type of jaw mechanism in a turtle is the posi- have used the Amphichelydia as a paraphyletic tion of the trochlea for the sliding cartilage taxon at best, characterized by variable mor- (cartilago transiliens) in the Bodenaponeurosis 408 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 155

cavum labyrinthicum

qu lateral head vein cavum tympani VII hyomandibular facial artery

Vlill posterior X = , _ | basis columelae eustachian tube

X ~~~~internal carotid artery trachea

FIG. 16. Chelydra serpentina, UT Chely 76. Transverse section through base of columella auris and fenestra ovalis in a cryptodire. This section is in about the same morphologic position as that in figure 17. Skull midline on left.

(main adductor tendon). In baenoids this involved in flooring the remnants of the cranio- trochlea is invariably in the same position as it is quadrate space (figs. 20-22). Furthermore, one of in cryptodires (fig. 23). There is no indication of the more prominent features of the cryptodiran a lateral process on the pterygoid for a trochlea akinetic condition involves the bracing of the as in pleurodires, and no structure is present that quadrate to the braincase by means of the ptery- could be considered intermediate to the pleuro- goid. A posterior expansion of the pterygoid diran condition. It can be concluded with a high forms this brace in both Recent cryptodires and degree of probability that the jaw mechanism of baenoids. living cryptodires and baenoids is identical. 3. Another feature related to the palato- 2. In discussing the differences between quadrate differences in cryptodires and pleuro- cryptodires and pleurodires the structure of the dires is the position of the hyomandibular branch palatoquadrate elements was stressed because of the facial nerve (VII). Baenoids lack a separate this area contains significant shared derived char- canal for the passage of this nerve as is found in acters. The structure of the pterygoid is par- pleurodires. There is complete agreement be- ticularly sensitive to these differences as it is tween cryptodires and baenoids in this feature 1 975 GAFFNEY: TURTLE PHYLOGENY 409

adductor mandibulae externus pars profundus

external adductor tendon

adductor mandibulae ) x externus pars superficialis

fl Aaantrum postoticum

ftrachea '~~~r' internal carotid artery

FIG. 17. Podocnemis expansa, UT POD III 227. Transverse sec- tion through base of columella auris and fenestra ovalis in a pleuro- dire. This section is in about the same morphologic position as that in figure 16. Skull midline on left. with no indication of a tendency toward the pterygoid (this is not completely certain, how- pleurodire condition in baenoids. ever) but in the Baenidae no sutures are visible. 4. The position of the mandibular artery is The fossa cartilaginis epipterygoidei is always not determinable in the fossil material. present in the Baenidae, however, and this sug- 5. The living cryptodires (with the ex- gests that the epipterygoid is either reduced and ception of Dermochelys) have an ossified epi- unossified in the adult (as in Dermochelys) or pterygoid that is usually well developed but is that it has become fused to the parietal. In any sometimes reduced. Pleurodires all lack epiptery- case, the condition seems to be very similar to goids. In addition, cryptodires characteristically that of other Cryptodira, since in the Pleurodira have a persistent part of the pterygoid cartilage the cartilage is reduced and apparently does not that occupies a small fossa cartilaginis epiptery- persist to maturity. goidei at the posterior end of the epipterygoid 6. Baenoids and testudinoids have very (see Gaffney, 1972b). Pleurodires also lack this similar articular surfaces, the area articularis man- structure. Glyptops seems to have a free epi- dibularis of chelydrids and baenoids being partic- 410 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 155

foramen palatinum posterius

,externus processus inferior

canalis cavernosus

foramen posterius canalis carotici interni

FIG. 18. Chelydra sepentina, AMNH (H.) 10446. Ventral view of a cryptodire with right pterygoid removed; stippling shows sutural areas and structures covered by pterygoid. Processus interfenestralis of opisthotic indicated by diagonal lines for a landmark. See figure 19. ularly similar. Baenoids are not known to have baenoids and cryptodires is in or near the poste- any features in this area that could be considered rior wall of the foramen palatinum posterius. In intermediate between cryptodires and pleuro- pleurodires the canal does not exit into the dires. foramen (the canal is absent in cheliids and exits 7. The foramen palatinum posterius, which on the ventral surface of tile pterygoid in pelo- transmits the inframaxillary artery from the medusids). interior of the skull to the ventral surface of the 9. The foramen supramaxillare of baenoids palate, is situated behind the orbit in pleurodires, is in the same morphological position as the apparently in conjunction with the development foramen supramaxillare of cryptodires. Pleuro- of a bony wall behind the orbit. Baenoids have dires lack the foramen, therefore, baenoids agree the foramen palatinum posterius ventral or with cryptodires in this feature. lateral to the orbit, the same position as it is in 10. Baenoids possess a prefrontal with a small cryptodires (with the exception of cheloniids in dorsal plate and only the ventral process remains. which the foramen is absent). There is no indi- Pleurodires lack the ventral process and have a cation in baenoids of a condition intermediate dorsal plate (which may also be small in cheliids). between cryptodires and pleurodires. The ventral process of most cryptodires is iden- 8. The anterior exit of the vidian canal in tical to the ventral process in baenoids. However, 1975 GAFFNEY: TURTLE PHYLOGENY 411

apertura narium interna

-foramen palatinum posterius

processusprocessusinferior parietalisparietalisIa 1 0 t1 foramen posterius canalis carotici interni ,: bs p

processus interfenestralis

FIG. 19. sp., AMNH (H.) 108954. Ventral view of a pleurodire with right pterygoid removed; stippling shows sutural areas and structures covered by pterygoid. Processus interfenestralis of opisthotic indicated by diagonal lines for a landmark. See figure 18. some trionychids have lost the ventral process so Russell, "1934" [1935]; Case, 1939; Gaffney, the agreement is not total, so far as cryptodires 1972a). A careful comparative study of baenoid are concerned. Nonetheless, baenoids could not and other fossil turtle neck vertebrae has yet to be considered intermediate or even tending be published but at the present time it seems toward pleurodires in this feature. most likely that the baenoid conditions represent Postcranial Characters. The cervical retraction primitive states in comparison with the mechanism in living turtles has been the most Eucryptodira. widely accepted and utilized character complex All known pleurodires have the pelvis sutured for the differentiation of higher categories of to the shell, whereas no cryptodire has this con- chelonians. The absence of a well-developed re- dition. Baenoids characteristically have a small traction device in Mesozoic forms has been one facet for the pubis on the xiphiplastron and this of the primary reasons for the recognition of the condition has been cited as an intermediate fea- Amphichelydia. Baenoids lack the cervical ture between cryptodires and pleurodires specializations of either living cryptodires or (Lydekker, 1889, pp. 517-518). However, this pleurodires. Older baenoids (Glyptops, Hay, does not appear to be even similar to the pelvis- 1908; Trinitichelys, Gaffney, 1 972a) have amphi- plastron relationship in pleurodires. The baenoid coelous cervical vertebrae but later forms have pubis lacks the ventral expansion seen in pleuro- formed articulations (Hay, 1908; Wiman, 1933; dires, and it seems to have had only a ligamen- 412 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 155

foramen nervi vidiani

foramen caroticum laterale - processus pterygoideus externus sulcus cavernosus -

foramen pro ramo nervi vidiani- foramen nervi vidiani

canalis caroticus internus internal carotid artery

foramen posterius canalis carotici interni FIG. 20. Chelydra serpentina, AMNH (H.) 107388. Dorsal view of right ptery- goid in a eucryptodire. See figures 21, 22. tous attachment with no sutural contact between only difference being the possibly movable ar- the pelvis and the plastron. The whole structure ticulation between the pubis and the plastron. is nearly the same as in a living cryptodire, the Pleurodires usually have an intergular scute 1975 GAFFNEY: TURTLE PHYLOGENY 413

processus pterygoideus externus

canalis caroticus lateralis

sulcus cavernosus

cristapterygoidea

foae nervi_trgmn canalis caroticus internus * foramen cavernosum foramen posterius canalis carotici >t 8 < foramen pro ramo nervi vidiani

internal carotid artery _ 2

\\\~~~foramenlateral head vein FIG. 21. Family Baenidae, genus indeterminate, Late , MCZ 3563 with added information from MCZ 3566. Dorsal view of right pterygoid in a paracryptodire. See figures 20, 22. between the paired gular scutes on the plastron, noids and in pleurodires (as well as in cheloniid whereas many cryptodires do not. Baenoids cryptodires) of an intergular scute probably usually have paired intergular scutes, but this represents the retention of a primitive character area is highly variable in individual shells as well and does not demonstrate a special relationship as between different taxa. The presence in bae- between them. 414 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 155

FIG. 22. Pelomedusa subrufa, AMNH (H.) 63581. Dor- sal view of right pterygoid in a pleurodire. See figures 20, 21. Baenoids and pelomedusid pleurodires possess bution of derived characters that baenoids have paired mesoplastral bones in the plastron, but no an ancestor in common with the Recent crypto- living cryptodire has these bones. However, it dires (Eucryptodira) that they do not share with seems likely that these elements are primitive other turtles. The following section deals with features of turtles and are not useful as shared relationships among the forms here recognized as derived characters in this context. cryptodires. In summary, I conclude from the above distri- 1975 GAFFNEY: TURTLE PHYLOGENY 415

processus trochlearis oticum B A

C internal carotid artery FIG. 23. Comparison of canalis caroticus internus (in black) in three major groups of turtles: A, Eucryptodira (Chelydra serpentina); B, Paracryptodira (Eubaena cephalica); C, Pleurodira ( sp.). The diameter of the canal is exaggerated for clarity. 416 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 155

THE PARACRYPTODIRA AND feature appears to have arisen independently in EUCRYPTODIRA the pelomedusid pleurodires. Some eucryptodires (e.g., toxochelyids, plesiochelyids) retain nasals When baenoids are compared with other fossil and some (, Collins, 1970;Desmato- and Recent cryptodires (table 4) certain con- chelys, Zangerl and Sloan, 1960) have prefrontals sistent characters emerge suggesting that most that do not meet in the midline. The post- nonbaenoid cryptodires are a monophyletic group. cranium of baenoids also has retained primitive The posterior flange on the pterygoid, charac- features: the cervical vertebrae are not modified teristic of cryptodires, is intimately involved with for neck retraction to the extent seen in most the path of the internal carotid artery. The eucryptodires, and mesoplastra and intergular position of the foramen posterior canalis carotici scutes are usually retained in baenoids but lost in interni is about midway along the length of eucryptodires. the pterygoid-basisphenoid suture in baenoids, whereas in the other cryptodires the foramen lies RELATIONSHIPS WITHIN THE at or near the posterior margin of the pterygoid EUCRYPTODIRA (fig. 23). Both arterial conditions are here con- The past 20 years have witnessed the general sidered to be derived with respect to the Crypto- recognition of three main groups of living cryp- dira as a whole but the primitive condition, as I todires: sea turtles, soft shell turtles (triony- interpret it, is unknown. However, a hypothetical chids), and plus the remaining fresh- ancestral condition can be speculated upon. I water forms. Wermuth and Mertens (1961) for- suggest that the two cryptodire groups diverged mally recognized these groups as superfamilies: before the posterior flange was completely de- Chelonioidea, Trionychoidea, and Testudinoidea. veloped, but after the development of a dif- The main departure from this sort of classifica- ference in positiop of the carotid artery. During tion has been the maintenance of separate super- further extension of the flange the carotid families for the highly derived living (plus became fixed in position. a few presumed fossil relatives) Dermochelys An alternative hypothesis is to consider one of coriacea and Carettochelys insculpta beginning -the known carotid positions primitive and the with Williams (1950) and continued by Romer other derived. The age and association of other (1956, 1966). Wermuth and Mertens include primitive characters with the baenoids suggest these forms in the Chelonioidea and Triony- consideration of the baenoid carotid pattern as choidea respectively, and in this section I present primitive with respect to the eucryptodires, but arguments that these two superfamilies (as con- the morphology does not substantiate this alter- strued by Wermuth and Mertens) are strictly native. Although the more anterior position of monophyletic. As with the preceding parts of the foramen posterior canalis carotici intemi in this paper, I am developing these hypotheses pri- baenoids agrees with the pleurodire condition marily on the basis of shared derived characters rather than with the eucryptodire condition, the in the skull. Nonetheless, postcranial features are bones forming the foramen are different (ptery- dealt with to some extent but this is mostly done goid and basisphenoid rather than prootic) and from the literature. the baenoid condition is not a structural inter- mediate between the pleurodire and eucryptodire conditions. Morphologic intermediates between SUPERFAMILY TRIONYCHOIDEA baenoid and eucryptodire carotid states are also McDowell (1961) and Albrecht (1967) stud- not known. ied the cranial arterial patterns in living turtles Other characters tend to support the con- with special reference to kinosternids and triony- tention that eucryptodires are the more derived chids. More recently Albrecht (unpublished ms) (or apomorphic) of the two groups. The nasals has increased the taxonomic breadth of the work. are usually lost and the prefrontals usually have and the major cranial arteries of turtles are now an expanded dorsal lappet that meets in the mid- relatively well known. The following shared de- line and occupies the position of the nasals. This rived character analysis of the arterial patterns 1975 GAFFNEY: TURTLE PHYLOGENY 417 agrees with some of the above authors' conclu- linked trionychids with kinosternids. I examined sions but not with others. Zug's morphologic descriptions and although it is In general two basic patterns of relative diam- difficult to determine primitive and derived eter size exist in the internal carotid system of states for most of the musculature characters, I living turtles (fig. 25). In one pattern (found in did find one character shared by kinosternids, trionychids, carettochelyids, kinosternids, and Dermatemys, and trionychids that is not found dermatemydids) the stapedial artery is distinctly in other turtles. The caudifibularis muscle exists smaller and a more medial branch of the internal only in those groups and would appear to be a carotid is larger, whereas in the other pattern good shared derived character (also noted by (found in all other turtles except living che- Frair, 1972). loniids) the stapedial artery is distinctly larger In view of the hypothesis that derma- and the more medial branches of the internal temydids, kinosternids, carettochelyids, and tri- carotid are smaller. McDowell (1961) and Al- onychids are a monophyletic group, I would brecht (1967) suggested that the pattern seen in extend the superfamily Trionychoidea to include living cheloniids, in which both arterial branches these families. Within this superfamily two sub- have about the same diameter, was primitive for groups may be recognized also on the basis of the turtles and that later turtles enlarged one or the arterial pattern. The kinosternids and Der- other branch. Comparison with other reptiles and matemys have enlarged the palatine artery while other turtle groups, however, does not substanti- the trionychids and Carettochelys have enlarged ate this notion. To begin with, other chelonioids, a more medial branch of the internal carotid (Zangerl, 1953, pl. 9 and personal (termed by Albrecht the pseudopalatine artery, observ.), (Casier, 1968, fig. 6 and per- but which appears to be in the same morphologic sonal observ.), and (personal ob- position as the orbital artery of kinosternids and serv.), have a small foramen caroticum laterale as testudinids). in testudinoids, and this indicates that the medial branch is reduced with respect to the stapedial SUPERFAMILY CHELONIOIDEA branch. More importantly, however, baenoids, pleurodires, and most living reptiles also have a Determining shared derived characters for liv- smaller palatine artery and a larger stapedial ing chelonioids (cheloniids and Dermochelys) is artery strongly suggesting that the cheloniid con- not too difficult. Nick (1912) and later workers dition is derived and not primitive for cryp- (Pehrson, 1945; Wegner, 1959; see their refer- todires or all turtles. The enlargement of the ences) have produced extensive studies of the medial internal carotid branch and the reduction head of Dermochelys comparing it with other of the stapedial artery then would appear to be a turtles, particularly cheloniids, and a number of derived character shared by dermatemydids, the characters presented may be used as shared kinosternids, trionychids, and carettochelyids derived characters for the group cheloniids plus and would imply that these groups share a com- Dermochelys. As opposed to the trionychoids mon ancestor not shared by other turtles. and the testudinoids, however, examination of A recent phenetic analysis of turtle hind-limb the fossil record reveals a considerable diversity morphology (Zug, 1971) also supports this of forms possibly related to the living chelonioids theory of relationships. Zug obtained measure- (see Romer, 1956, pp. 507-512, for a summary). ments of the distribution of muscle attachment Although much of this fossil material is repre- sites and osteology of the pelvic girdle and hind sented by skulls with well-preserved basicrania, limb in a series of modern turtles. He then very little of it is prepared to the extent neces- entered this information into a computer pro- sary for comparisons to be made using the cri- gram designed to determine overall phenetic simi- teria developed for the living forms. Further- larity between the included taxa for these charac- more, the most derived of the living forms, ters. Even though the trionychids and Derma- Dermochelys, has apparently utilized neoteny as temys are categorized as swimmers and the kino- a modifying mechanism, and the cartilaginous sternids as bottom walkers, the similarity method nature of much of the skull makes comparison 418 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 155 with fossil forms difficult, since cartilage is usu- ally not preserved in fossils. The region around the basisphenoid appears to offer the best derived characters applicable tb fossil and Recent chelonioids. Nick (1912), Pehrson (1945), and Zangerl (1953) have been the principal developers of these criteria, and I think that together with considerations of post- cranial morphology (see below) they offer a good complex of shared derived characters. 1. The ossified trabeculae lie close together for their whole length and are partially or com- pletely fused to form a rostrum basisphenoidale. 2. The foramina anterius canalis carotici interni are close together and separated by a rela- tively thin bar of bone. 3. The sella turcica is reduced or absent due to approximation of the trabeculae or ossifica- FIG. 24. Diagrammatic dorsal view of a turtle tion of the taenia intertrabecularis (see below). head showing relative diameters and positions of 4. The dorsum sellae is high and separated branches of the internal carotid artery. The ar- from the sella turcica and foramina anterius terial pattern shown here is suggested as the canalis carotici interni by a prominent bone sur- primitive condition for turtles and is repeated as face that usually has a sagittal ridge. In the other A in figure 25. superfamilies the dorsum sellae overhangs the sella turcica. able for fossil chelonioids and the following The state of the above characters is relative forms are known to possess the above characters: and their condition is meaningful only in com- Toxochelys moorevillensis (Zangerl, 1953), Tox- parison to the other cryptodire superfamilies. ochelys latiremis (AMNH 1042 and 1835), The above features are seemingly interrelated and Ctenochelys tenuitesta (Zangerl, 1953), Rhino- may be explained by the presence of a structure, chelys sp. (Collins, 1970), Eochelone brabantica the taenia intertrabecularis, that Nick (1912) and (Casier, 1968), Puppigerus camperi (Moody, Pehrson (1945) described. This structure, a rod- 1974), Corsochelys haliniches (Zangerl, 1960), like element positioned in the midline just above and Notochelone costata (Queensland Museum the trabeculae and anterior to the dorsum sellae, F6587). is found only in the cheloniids and Dermochelys As I interpret the postcranial characters used among living turtles. In Dermochelys it does not by previous workers, two character complexes, ossify (as is the case with much of the basicranial the forelimbs and the shell, emerge as potential morphology) and must be studied in cartilagi- derived characters for the Chelonioidea. The nous preparation (or sections, as provided by development of a flipper-type locomotion in the Nick). In living cheloniids the taenia intertra- front limbs has involved a series of changes that becularis ossifies as part or all of the rostrum are recognizable to a varying degree. For ex- basisphenoidale resulting in the obliteration of ample, Zangerl has argued (1953) that although the sella turcica. The actual presence of a taenia toxochelyid front limb and girdle elements lack intertrabecularis in fossils is difficult to demon- the extreme modifications seen in the living strate because developmental information is cheloniids, they do possess changes in a flipper really necessary for its identification but in any direction in comparison to Chelydra and other case the list of characters is valid whether or not testudinoids. Zangerl and Sloan (1960, pp. they are related to the taenia intertrabecularis. 34-38) use features of the limb complex as the Some information on the basicranium is avail- primary basis for a diagnosis of the Chelonioidea 1975 GAFFNEY: TURTLE PHYLOGENY 419

,~~~~~~~~~~~,.II

4A

I AI

FIG. 25. A cladogram showing relationships of trionychoid turtles based on arterial patterns in the head. A, primitive condition for turtles; B, pattern found in and ; C, pattern found in Carettochelyidae and . See figure 24 for identification of arteries. and consider that the families Toxochelyidae, but here the determination of homologous fea- , , and tures appears more difficult than with the fore- possess these features in varying degrees. limb. Strictly speaking one can assume that fon- Shell morphology has also been a classic tanelle development is derived with respect to a source of characters for differentiating sea turtles solid shell for all turtles, but further use of shell 420 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 155

q0 0F 0, \NO~~~~~~A1/ a

Internal carotid artery enters skull at posterior Internal carotid artery end of pterygoid enters skull midway along- pterygoid-basisphenoid suture Jaw muscle trochlea on Jaw muscle trochlea on -otic chamber, pterygoid pterygoid, quadrate braces braincase braces braincase Closed interpterygoid --vacuity, middle ear with lateral wall formed by quadrate

Shell, loss of teeth, middle -ear hypertrophy, (?) akinesis FIG. 26. A theory of relationships among the higher categories of turtles. This cladogram indicates the relative position of common ancestors and a few shared derived characters diagnostic of particular lineages. Other morphologic and temporal parameters are not expressed. reduction is difficult. Most chelonioid shells, par- would be a good derived character. In that case, ticularly plastra, are reduced in some ways but however, independent reduction would have had determining primitive and derived states between to take place in at least three different lines- them and forms such as Chelydra and Macro- pleurodires, baenoids, and noncheloniid chelo- clemys is difficult. nioids to say nothing of other reptiles. My inter- pretation, then, of the testudinoid arterial pat- tern is that it is primitive for turtles and, there- SUPERFAMILY TESTUDINOIDEA fore, not useful for arguing the monophyletic I have attempted to show that the two previ- nature of the Testudinoidea. ous superfamilies can be hypothesized as mono- phyletic units on the basis of shared derived char- acters. However, the Testudinoidea have no THE EARLY HISTORY OF TURTLES shared derived characters that I have been able to Turtles have long been considered a "primi- find. If the argument that the cheloniid arterial tive" or relict reptile group that has maintained a pattern is primitive for eucryptodires is correct consistent morphologic structure since its origin, then the reduction of the medial carotid branch but an alternative interpretation of chelonian 1975 GAFFNEY: TURTLE PHYLOGENY 421

(Recent)

Cervicals specialized for retraction III

() experimentation in cervical retraction

Akinetic specializations present in skull Limbs specialized. 11 Cervicals unspecialized

experimentation in akinesis

(Late Triassic)

Shell fully developed. Skull lacking akinetic I specializations Limbs and cervicals unspecialized.

FIG. 27. A speculative history of turtle adaptations in terms of levels of organization (see text for explanation). Major horizontal divisions refer to adaptive levels and not to stratigraphic units. Approximate stratigraphic age is indicated on the right. history may be more accurate. It seems more 1. Nonhomologous trochlear structure in the likely that two major lineages (cryptodires and jaw mechanism pleurodires) arose early in the history of turtles 2. Method of bracing palatoquadrate elements and passed through similar stages during their to braincase phylogeny and repeatedly evolved parallel adap- 3. Position of structures in cranioquadrate tations. Furthermore, as opposed to previous space ideas on conservativism in turtles, a number of 4. Epipterygoid unique and structurally profound adaptations 5. Position of foramen palatinum posterius. arose throughout chelonian history. The trochlear apparatus of turtles is unique As the preceding comparison of pleurodires among vertebrate adductor systems and has, and cryptodires emphasizes, most of the cranial apparently, evolved in conjunction with the differences between the two groups are related to expansion of the otic region. The paracapsular the palatoquadrate elements. The differences are network, a fluid filled sinus in the middle ear of summarized below: turtles, is hypertrophied compared with most 422 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 155

other tetrapods and is enclosed in a chamber quadrate ramus of the pterygoid does not send formed from palatoquadrate and braincase ele- any flange inward to floor the cranio-quadrate ments. The development of this otic chamber passage as in all other known turtles [actually reduced the space for the adductor musculature only in cryptodires; pleurodires have a flange of and probably stimulated the formation of the the quadrate flooring the cranio-quadrate space trochlear apparatus. The trochlear system is a and bracing the palatoquadrate against the brain- mechanism for translating anteroposterior forces case], and the foramina for the vena capitis into a vertical plane, enabling the adductor lateralis, the internal carotid, and the stapedial musculature to insert above and behind the artery, as well as the fenestra ovalis are all expanded otic chamber. The morphology of the exposed in ventral view" (Parsons and Williams, trochlear apparatus in pleurodires and crypto- 1961, p. 91). Kinesis may or may not have been dires is different but the mechanism is the same, present. As far as can be determined, then, the suggesting that the lineages diverged before the Triassic Proganochelys supports the hypothesis development of the trochlea but after the be- advanced here and presents us with a good mor- ginning of ear hypertrophy. Akinesis probably phologic ancestor for cryptodires and pleuro- preceded or directly followed trochlear forma- dires. tion because of the close relationship between Following Proganochelys, there was a prob- the quadrate and the paracapsular system. The able period of experimentation during the devel- method of achieving akinesis, as in the method of opment of advanced features of akinesis and a trochlear formation, is different in cryptodires trochlear mechanism. During or before this and pleurodires, again suggesting independent period the pleurodire and cryptodire lineages acquisition. The different position of structures split. The next level (II) is characterized by traversing the space (the cranioquadrate space) akinetic skulls, specialized limbs, and unspecial- between the palatoquadrate and the braincase in ized cervical vertebrae. The two lineages were the two groups, and the development of a ptery- essentially "modem" in all aspects of their osteol- goid brace in cryptodires and a quadrate brace in ogy except the neck. In the Late Jurassic and pleurodires are significant indications that cryptodire cervicals appear to akinesis was attained independently in the two lack formed central articulations (they are groups. Thus, the differences between crypto- amphicoelous) but in the Late Cretaceous dires and pleurodires can be interpreted as arising formed centra appear and one double-jointed in two closely related lineages that were subject centrum (an advanced cryptodiran feature) is to similar selection pressures and evolved similar, known from the Maestrichtian Hell Creek but not homologous, structures in response to Formation (R. Estes, personal commun.). Some these selection pressures. Late Cretaceous pleurodire vertebrae (Taphros- A summary of the possible events in the phys, Maestrichtian, New Jersey) are still more history of chelonians can be assembled from the primitive than Recent pleurodire cervicals but are above interpretations and current knowledge of definitely specialized in that direction, whereas the fossil record (fig. 27). Proganochelys (Jaekel, other Cretaceous pleurodire vertebrae (Podo- 1916; Parsons and Williams, 1961; Romer, 1966) cnemis, Wood, personal commun.) appear identi- shows that turtles evolved the shell before the cal to some living pleurodires. The latest period skull, vertebrae, and limbs were characteristically of chelonian history (level III) then, is charac- modified. The skull at this stage (level I in fig. terized by the fully developed cervical retractile 27) lacked marginal teeth and in life probably mechanisms that are the most obvious feature of had a horny bill as in Recent turtles. However, living cryptodires and pleurodires. the palatoquadrate elements, particularly the structures related to the cranioquadrate space, do CLASSIFICATION not seem to be modified in either the crypto- diran or pleurodiran manner: "Posteriorly also Most controversy and misunderstanding con- the situation is primitive; [inProganochelys] the cerning cladism arises from classification rather 1975 GAFFNEY: TURTLE PHYLOGENY 423

TABLE 1 A Comparison of Captorhinus and Turtles Character Captorhinus Testudines Maxillary and mandibular teeth Well-developed Absent or rudimentary Basipterygoid articulation Movable Fuseda Hypertrophy of middle ear Absent Present Pineal foramen Present Absentb Ectopterygoid AbsentC Absent Lacrimal, postfrontal, supratemporal, postparietal, septomaxilla Present Absentd Vomer Paired Single Processus paroccipitalis of opisthotic sutured to quadrate No Yes

aPossibly movable in Proganochelys; see discussion under Proganochelydia. bPresent as an abnormality in some forms-Zangerl, 1957. cPresent in other Captorhinomorpha. dSee discussion under Proganochelydia. than phylogeny reconstruction. Although nearly phylogeny (as a useful, testable hypothesis, that all systematists emphasize the importance and is), but finds my classification radical, imprac- value of classification, there is little agreement, tical, or simply offensive, then I would urge even among cladists, as to the specific procedures ignoring my classification. or governing principles used in erecting a classi- fication. In my opinion a phylogenetic diagram, CLASSIFICATION OF RECENT AND cladistic or not, is more useful and to be pre- FOSSIL TURTLES ferred over a classification for most biologic pur- poses. Arguments for or against a particular ORDER TESTUDINES1 LINNAEUS, 1758 classification in a situation where the phylogeny Diagnosis. sauropsids with mandib- is essentially agreed upon by the persons involved ular and maxillary teeth rudimentary or absent, seems fruitless. Nonetheless, I am here proposing functionally replaced by a horny sheath, basi- a new classification of turtles. This classification pterygoid articulation fused (see discussion under differs from previous ones because I have tried Proganochelys); middle ear hypertrophied for the to maintain strictly monophyletic taxa to the housing of a fluid-filled paracapsular sinus; pineal extent that this is possible. For the most part foramen absent; ectopterygoid, postfrontal, previously erected taxa are maintained and supratemporal, postparietal, and septomaxilla phylogeny is reflected by the addition of new absent; vomer single; lacrimal duct absent; categories at intermediate levels. My only pur- processus paroccipitalis of opisthotic sutured to pose in this classification is the naming of mono- quadrate. phyletic groups and the reflection of the phylo- Discussion. Romer (1956, p. 495) should be genetic hypotheses advanced here. consulted for the rather useful postcranial fea- The erection of new categories (i.e., Parv- tures diagnostic of turtles. The cranial features order) is not unusual, but it is rarely done by listed above would probably be amplified con- vertebrate systematists. After I decided on a siderably if the Triassic proganochelyids were strictly monophyletic classification, it was a better known. I have tried to indicate here those question of how to express this in the idiom of characters that would be most important in a the Linnaean hierarchy. I have chosen to do this comparison of turtles and captorhinomorphs by maintaining previously named monophyletic (see table 1). groups at "conventional" levels and inserting new categories where necessary. If one accepts my 'Hunt (1958) discussed the ordinal name for turtles. 424 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 155

TABLE 2 A Comparison of Proganochelydia and Casichelydia Character Proganochelydia Casichelydia Floor of cavum acustico-jugulare Open Closed Interpterygoid vacuity Open Closed Middle ear (cavum acustico-jugulare) with lateral wall formed by Absent Present quadrate Cultriform process on parasphenoid Present Absent Palatal teeth Present Absent Apertura narium externa divided by dorsal process of premaxillae Yes No (see discussion) Expanded crista supraoccipitalis Absent Present Antrum postoticum Absent Present Well-developed median tubercle on (?) basioccipital Present Absent

The presence of a fused basipterygoid articu- SUBORDER PROGANOCHELYDIA ROMER, 1966 lation in Proganochelys is based solely on my Diagnosis. Turtles with open interpterygoid interpretation of the figures given by Parsons and vacuity and cultriform process; floor of cavum Williams. Poor preservation or preparation could acustico-jugulare open; middle ear (essentially very well make a kinetic skull look akinetic and the cavum acustico-jugulare) without a lateral this doubt should also be kept in mind. wall formed by the quadrate; kidney-shaped The suggestion made by Lydekker (1889) that cavum tympani absent; palatal and rudimentary some "amphichelydians" had the pelvis partially marginal teeth present; apertura narium externa fused to the plastron has been shown (see pre- divided by dorsal processes of premaxillae; crista ceding section on baenoids) to be in error, and supraoccipitalis not developed as in other turtles; the pelvis in , , and antrum postoticum absent; well-developed baenoids is free from sutural contacts with the median tubercle on (?) basioccipital; lacrimal shell. I have not been able to find any turtles apparently present. with a pelvis that is neither completely fused Discussion. The above characters are for the with the shell as in pleurodires nor free as in most part based on the works of Jaekel (1916) cryptodires and I advance the suggestion (see and Parsons and Williams (1961). The latter au- discussion of Pleurodira) that the fused pelvis thors have particularly modified knowledge of may be a derived character for pleurodires. Pro- Proganochelys, but the cranial morphology of terochersis Fraas (1913) from the Late Triassic that form still awaits thorough description. A fig- of Germany has usually been included with Pro- ure in Romer (1966, fig. 166) also changes ganochelys but it has a pelvis that is fused to the previous ideas about the skull of Proganochelys. shell. The original description and a good cast This figure shows no supratemporal or post- (AMNH 3867) show a pelvic morphology that frontal elements, absent in all later turtles but agrees closely with other pleurodires. Fraas origi- long presumed to be present in Proganochelys. If nally identified this form as a pleurodire, and the correct, the 1966 figure shows that the only only basis for removing it from the Pleurodira "extra" bone present in Proganochelys is the seems to be its age and the presence of pre- lacrimal, and that is indicated by a dashed suture. sumably primitive characters such as two pairs of In the above diagnoses of Testudines and Pro- mesoplastra. Cranial material may clarify the ganochelydia I have assumed that this figure is relationships of Proterochersis but presently no correct; however, I do not know if it is based on one has successfully negated the hypothesis that original examination of the specimen or inter- Proterochersis shares an ancestor with other pretation of the photographs. There is, therefore, Pleurodira. In any case, I am specifically remov- some doubt about these features. ing it from the Proganochelydia which, for the 1975 GAFFNEY: TURTLE PHYLOGENY 425 present, rests entirely on the forms described by some to be another superfluous higher taxon of Jaekel (1916) and Parsons and Williams (1961). turtles (for example, see Bergounioux, 1955; Zangerl, 1969; Chkhkvadze, 1970) is defended SUBORDER CASICHELYDIA GAFFNEY, 1975a here only on the assumption that a classification should completely reflect phylogenetic Diagnosis. Turtles with closed interpterygoid relation- ships. This group is monophyletic and can be vacuity and no trace of cultriform process on recognized by a series of shared derived char- parasphenoid (parasphenoid nearly always fused acters, and that is why I have named it. with basisphenoid); floor of cavum acustico- The name has been coined from two Greek jugulare with lateral wall formed by quadrate; words, kasis-sister or brother-and chelys-tur- kidney-shaped cavum tympani present; all indi- tle-in allusion to the supposition that this is the cations of teeth absent; apertura narium externa sister group of the Proganochelydia. usually not divided; crista supraoccipitalis ex- panded dorsally in and/or posteriorly comparison INFRAORDER PLEURODIRA (COPE, 1868) with other reptiles; antrum postoticum present; median tubercle on basioccipital absent; lacrimal Diagnosis. Casichelydians with trochlear sur- absent. face for cartilago transiliens developed on lateral Discussion. The erection of what may seem to process of pterygoid; processus trochlearis ptery-

TABLE 3 A Comparison of Cryptodires and Pleurodires Character Cryptodira Pleurodira Trochlear surface upon which A true synovial capsule formed on A joint surface consisting of the cartilago transiliens articulates the processus trochlearis oticum, infolded oral mucosa formed on the anterior edge of the otic the lateral process of the chamber pterygoid Bracing of quadrate to braincase Pterygoid extends posteriorly be- Quadrate sends a ventral process tween quadrate and braincase medially to the braincase Position of hyomandibular branch Traverses the canalis cavernosus Travels outside the canalis of facial nerve (VII) in the cavernosus in its own canal for cranio-quadrate space most of the distance Position of mandibular artery Usually exits from foramen nervi Does not exit from foramen nervi trigemini, usually travels trigemini, branches off through canalis cavernosus stapedial artery after latter exits from foramen stapedio- temporale, does not travel through canalis cavernosus Epipterygoid Present (except in Dermochelys), Absent, pterygoid cartilage not pterygoid cartilage persistent persistent, fossa cartilaginis in fossa cartilaginis epipterygoidei epipterygoidei greatly reduced or absent Lower jaw articulation Lacks hemispherical articular Usually has hemispherical articular Foramen palatinum posterius In floor of orbit (absent in Behind orbit cheloniids) Anterior exit of the canalis nervi In posterior wall of foramen Absent in cheliids, in ventral surface vidiani palatinum posterius of pterygoid in pelomedusids Descending process of prefrontal Yes No meets vomer ventromedially 426 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 155 goidei never on otic chamber; joint surface of pelvis, the cryptodiran cranial features are in- trochlea consisting of infolded oral mucosa variably associated with a free pelvis and pleuro- rather than true synovial capsule; quadrate send- diran cranial features with the sutured pelvis. ing process medially to braincase elements, ptery- Supposed partially sutured pelves (e.g., Plesio- goid rarely extending posteriorly but in any case chelys, Pleurosternon) actually have the free con- not preventing quadrate contact with braincase; dition and lack any sutural connection. hyomandibular' nerve contained in own canal Platychelys oberndorferi (see Bram, 1965) separate from canalis cavernosus; mandibular from the Late Jurassic of Europe can be identi- artery failing to exit from foramen nervi tri- fied as a pleurodire because it has a sutured gemini but branching off stapedial artery after pelvis. Its other features, a single pair of meso- latter leaves otic region of skull to enter temporal plastra and an intergular scute, are primitive fossa; epipterygoid not ossifying, epipterygoid chelonian features also occurring in baenoids and cartilage apparently absent or greatly reduced in pleurodires. Proterochersis (see discussion above) adult, fossa cartilaginis epipterygoidei therefore from the Late Triassic can also be postulated as a greatly reduced or absent; articular usually hemi- pleurodire. This form is older and has other spherical; foramen palatinum posterius behind primitive or perhaps uniquely derived features in orbit; descending process of prefrontal reduced, its shell but again, assuming that a fixed pelvis is not meeting vomer ventromedially. a derived character and, in the absence of con- Head withdrawn by horizontal flexure of neck flicting derived characters, the hypothesis that in advanced forms with attendant development of these forms are pleurodires cannot be negated. narrowly spaced zygapophyses,laterally developed transverse processes, and formed central articu- INFRAORDER CRYPTODIRA (COPE, 1868) lations; pelvis suturally united to carapace and plastron; cervical (nuchal) scute, intergular scute Diagnosis. Skull with trochlear surface for and mesoplastra present or absent. cartilago transiliens developed on processus Discussion. I have discussed most of the above trochlearis oticum, never on process of ptery- features earlier in this paper, but the absence of a goid; pterygoid extending posteriorly between posterior extension on the pterygoid appears to quadrate and braincase; hyomandibular nerve have an exception in a Cretaceous pleurodire, traversing cranioquadrate space in canalis caver- (Gaffney and Zangerl, 1968), and nosus; mandibular artery usually exiting from needs to be dealt with. In Bothremys the articu- foramen nervi trigemini; epipterygoid usually lation with the lower jaw is on a level posterior present, when absent pterygoid cartilage per- to the occipital condyle, a very rare condition in sistent, resulting in fossa cartilaginis epiptery- pleurodires and presumably specialized. The goidei; no development of hemispherical articular relations of the quadrate and the neurocranial on lower jaw; foramen palatinum posterius in elements are still basically the same as in other floor of fossa orbitalis; vidian nerve exiting in or pleurodires but the posterior movement of the near foramen palatinum posterius (absent in quadrate has "pulled" the quadrate ramus of the cheloniids); descending process of prefrontal pterygoid posteriorly. The pterygoid flange of meeting vomer ventromedially. cryptodires is still entirely absent and Bothremys Head withdrawn by vertical flexure of neck in is not an exception to the characters listed. advanced forms with attendant development of The sutural union of all three pelvic bones widely spaced zygapophyses, reduced transverse with the shell appears to be a good shared processes, and formed central articulations; these derived character for pleurodires. The free pelvic features absent or slightly developed in primitive condition presumably precedes the fused one members; pelvis not suturally united to carapace and, until some argument is developed to the and plastron; cervical (nuchal) scute usually contrary, the free condition can be hypothesized present; intergular scute absent in advanced as primitive and the fused one as derived. forms, present primitively; mesoplastra absent in Furthermore, of taxa known from both skull and advanced forms, present in primitive members. 1 975 GAFFNEY: TURTLE PHYLOGENY 427

TABLE 4 A Comparison of Paracryptodira and Eucryptodira

Character Paracryptodira Eucryptodira Position of foramen posterius Midway along length of Posterior end of pterygoid canalis carotici interni basisphenoid-pterygoid suture Prefrontals meet on skull roof No Yese midline Nasals Present Usually absent Cervical vertebrae Not fully retractile Usually fully retractile Mesoplastra Present Absent

aNot in some specimens of Rhinochelys (Collins, 1970) and Desmatochelys (Zangerl and Sloan, 1960).

Discussion. It should be noted that I made an rius canalis carotici interni occurring midway error in the original published diagnosis of along the pterygoid-basisphenoid suture. cryptodires (Gaffney, 1972a, p. 249). The fifth Meiolaniids have been considered baenoids and sixth lines of the diagnosis which read: "hyo- but an examination of basicrania ( mandibular nerve in its own canal traversing platyceps, Austrialian Museum F 208B, F 1209, cranio-quadrate space... ." should read as fol- F 43183; Crossochelys corniger, AMNH 3161; lows: -"hyomandibular nerve traverses cranio- see also Anderson, 1925, and Simpson, 1938) quadrate space in canalis cavernosus..." suggests that they are eucryptodires. The foramen posterius canalis carotici interni lies at PARVORDER PARACRYPTODIRA GAFFNEY, the posterior edge of the pterygoid, the most NEW important diagnostic character of the Eucrypto- Diagnosis. Cryptodiran turtles tending to dira. retain primitive features; skull with nasals; pre- frontals not meeting on skull roof midline; PARVORDER EUCRYPTODIRA GAFFNEY, 1975a foramen posterius canalis carotici intemi lying Diagnosis. Cryptodiran turtles tending to midway along length of basisphenoid-pterygoid possess advanced features in comparison with suture; well-developed stapedial artery, reduced Paracryptodira; skull often without nasals; pre- orbital and palatine arteries (inferred from frontals nearly always meeting on skull roof mid- foramina); cervical vertebrae lacking well- line; foramen posterius canalis carotici interni developed retraction mechanism, early forms lying at or near posterior edge of pterygoid and lacking formed central articulations; shell with usually formed primarily by pterygoid; stapedial, mesoplastra and paired intergular scutes. orbital, and palatine arteries varying from primi- Discussion. The category "parvorder" is de- tive condition (see Paracryptodira) to various rived at the suggestion of McKenna from the derived conditions involving reduction of stapedial Latin word parvus-little. The Paracryptodira artery and/or enlargement of more anterior comes from the Greek para-near, beside-com- carotid branches; cervical vertebrae characteristi- bined with the Greek derived Cryptodira in allu- cally with formed central articulations adapted sion to its relationships with the Eucryptodira. for skull retraction in vertical plane; transverse Essentially, the Paracryptodira consists of the processes usually reduced, zygapophyses usually Baenoidea as defined in a paper by me (Gaffney, placed laterally, primitive forms possibly even 1972a). Since the publication of that paper I amphicoelous, however; shell usually with fewer have examined a newly prepared specimen of bones and scutes that in Paracryptodira, meso- Kallokibotium (Nopsca, 1923) that shows the plastra and intergular scutes usually absent. diagnostic baenoid features of the foramen poste- Discussion. The term "eucryptodira" is formed 428 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 155

TABLE 5 A Comparison of the Eucryptodire Superfamilies

Character Trionychoidea Chelonioidea Testudinoidea

Stapedial artery reduced or absent Yes No No Foramen stapedio-temporale reduced or absent Often No No Dorsal process on palatine present Yes No Noa Ossified trabeculae of rostrum basisphenoidale lie close No Yes No together or are fused Foramina anterius canalis carotici interni lie close together No Yes Rarely Sella turcica reduced or obliterated No Yes No Dorsum sellae high and separated from sella turcica by bone No Yes No surface Posterior portion of sella turcica concealed by overhanging Usually No Yes dorsum sellae Caudifibularis muscle present Yes No No

aSmall process present in some Batagurinae. from the Greek eu-true plus cryptodira-in inent bone area in contrast to most Chelonioidea; allusion to the idea that members of this group sella turcica well developed, not reduced; dorsum typically (but not universally) have well-devel- sellae low and overhanging foramina anterius oped retractile neck mechanisms. canalis carotici interni and concealing posterior Although I am here proposing three super- portion of sella turcica, bone surface as seen in families in the Eucryptodira, there are other Chelonioidea not developed; caudifibularis muscle forms recognizable as eucryptodires, but not present. members of these superfamilies. For example, IncludedFamilies. Kinosternidae, Dermatemy- Solnhofia (Gaffney, 1975b) and the meiolaniids didae, Carettochelyidae, Trionychidae. can be identified as eucryptodires but I cannot be more specific about their relationships. SUPERFAMILY CHELONIOIDEA BAUR, 18931 Diagnosis. Eucryptodires with well-developed stapedial artery reflected by a relatively large SUPERFAMILY TRIONYCHOIDEA GRAY, 1870 foramen stapedio-temporale; foramen posterius Diagnosis. Eucryptodires with distinctly re- canalis carotici interni and canalis caroticus inter- duced stapedial artery, usually (but not always) nus usually smaller in diameter than in Tri- reflected by a reduction or loss of foramen stape- onychoidea but sometimes larger than in Testudi- dio-temporale and canalis stapedio-temporalis; noidea; foramen anterius canalis carotici interni foramen posterius canalis carotici interni and as in Testudinoidea and never enlarged as in Tri- canalis caroticus internus relatively larger in diam- onychoidea but foramen caroticum laterale (and eter in comparison with those structures in palatine artery) enlarged in Cheloniidae; palatine Testudinoidea; foramen caroticum laterale or without dorsal process; ossified trabeculae of foramen anterius canalis carotici interni con- basisphenoid usually close together or fused into spicuously enlarged in comparison with these rodlike rostrum basisphenoidale; foramina ante- structures in Testudinoidea; palatine usually with rius canalis carotici interni close together and variably developed dorsal process that contributes separated by relatively thin bar of bone; sella tur- to side wall of braincase (cavum epiptericum); cica reduced or obliterated due to approximation ossified trabeculae of basisphenoid well separated of trabeculae and/or development of taenia inter- lateral to a prominent sella turcica and not fused 'Kuhn (1964) indicated "Baur 1889" as the original into rodlike rostrum basisphenoidale; foramina appearance of this name but I have been unable to anterius canalis carotici interni separated by prom- find this name in any of Baur's papers before 1893. 1975 GAFFNEY: TURTLE PHYLOGENY 429 trabecularis; dorsum sellae high and separated anterius canalis carotici intemi and foramen caro- from sella turcica and foramina anterius canalis ticum laterale distinctly smaller in diameter than carotici interni by prominent bone surface that foramen stapedio-temporale; palatine usually usually has a sagittal ridge; posterior portion of without dorsal process (small process present in sella turcica not concealed by overhanging dor- some Batagurinae); ossified trabeculae of basi- sum sellae; caudifibularis muscle absent. sphenoid usually well separated lateral to prom- Included Families. (Gaffney, inent sella turcica and not fused into rodlike 1 975a), Toxochelyidae, Protostegidae, Dermo- rostrum basisphenoidale; foramina anterius canalis chelyidae, and Cheloniidae. carotici interni usually separated by prominent bone area in contrast to most Chelonioidea; SUPERFAMILY TESTUDINOIDEA BAUR, 1893 sella turcica well developed, not reduced; dor- sum sellae low and overhanging foramina anterius Diagnosis. Eucryptodires with well-developed canalis carotici interni and concealing posterior stapedial artery reflected osteologically by rela- portion of sella turcica; bone surface as seen in tively large foramen stapedio-temporale and Chelonioidea not developed; caudifibularis muscle canalis stapedio-temporalis; foramen posterius absent. canalis carotici interni and canalis caroticus inter- Included Families. (plus Platy- nus distinctly smaller in relative diameter than sternon, Gaffney, In press), , Testu- those structures in Trionychoidea; foramen dinidae.

A CLASSIFICATION OF TURTLES Order Testudines Linnaeus, 1758 Suborder Proganochelydia Romer, 1966 Family Proganochelyidae (Triassic) Suborder Casichelydia Gaffney, 1975a Infraorder Pleurodira (Cope, 1868) Family (Cretaceous-Recent) Family (Eocene-Recent) Infraorder Cryptodira (Cope, 1868), Parvorder Paracryptodira, new Superfamily Baenoidea Williams, 1950 Family Glyptopsidae (Jurassic) Family Baenidae (Cretaceous-Eocene) Parvorder Eucryptodira Gaffney, 1 975a Superfamily Trionychoidea Gray, 1870 Family Kinosternidae (Oligocene-Recent) Family Dermatemydidae (Cretaceous-Recent) Family Carettochelyidae (Eocene-Recent) Family Trionychidae (Cretaceous-Recent) Superfamily Chelonioidea Baur, 1893 Family Plesiochelyidae (Jurassic) Family Protostegidae (Cretaceous) Family Toxochelyidae (Cretaceous-Eocene) Family Dermochelyidae (Eocene-Recent) Family Cheloniidae (Cretaceous-Recent) Superfamily Testudinoidea Baur, 1893 Family Chelydridae (Paleocene-Recent) Family Emydidae (?Paleocene-Recent) Family Testudinidae (Eocene-Recent) SUMMARY Basicranial characters provide the basis for a dorsum sellae high and does not overhang caro- new theory of relationships among major groups tid foramina, carotid foramina closely apposed. of Recent and extinct turtles. The method used The Chelonioidea contains the Plesiochelyidae, here to develop phylogenetic hypotheses is based Protostegidae, Toxochelyidae, Dermochelyidae, on the distribution of shared derived characters; and Cheloniidae. The primary shared derived a strategy expounded by Hennig (1966) and character defining the superfamily Trionychoidea others and often called cladism or phylogenetic is the reduction or absence of the stapedial ar- systematics. Although I emphasize phylogenetic tery. The families Kinosternidae, Derma- reconstruction I also present a new classification temydidae, Carettochelyidae, and Trionychidae of turtles that consists of strictly monophyletic are placed in the Trionychoidea on this basis. I groups (to the extent that I can determine them) have not been able to diagnose the superfamily and is a direct reflection of the phylogeny. Testudinoidea using shared derived characters 1. Shared derived characters diagnostic of and the group may be paraphyletic because it is the order Testudines include: a shell, loss of mar- delimited only by primitive features. The families ginal teeth, middle ear hypertrophy, and prob- Testudinidae, Emydidae, and Chelydridae make ably akinesis. up the Testudinoidea. 2. Two suborders are recognized within the The "Amphichelydia" is a higher taxon char- Testudines. The suborder Proganochelydia con- acterized by primitive features and supposedly sists of the Triassic genus Proganochelys and is containing the ancestors of Recent turtles. The characterized by predominantly primitive fea- development of a strictly monophyletic classifi- tures such as an open interpterygoid vacuity and cation requires the rejection of this taxon and a laterally open middle ear cavity. All other tur- the redistribution of its included taxa. tles are contained in the suborder Casichelydia Although most turtle fossils consist only of which can be diagnosed using shared derived shells or shell fragments, there are a sufficient characters; the most important being a closed in- number of skull-shell associations to allow the terpterygoid vacuity and a middle ear with the development of a speculative history of the lateral wall present. group. The acquisition of a shell (Late Triassic or 3. The Casichelydia consists of two infra- earlier) preceded the characteristic akinetic modi- orders. The infraorder Pleurodira possesses the fications (although kinesis may have actually following shared derived characters: jaw muscle been lost at that time or earlier) and the develop- trochlea on pterygoid, quadrate braces braincase. ment of cervical and limb specializations. Adap- The infraorder Cryptodira has these shared de- tations for cervical retraction (Late Cretaceous) rived characters: jaw muscle trochlea on otic appear well after the akinetic and palatoquadrate chamber, pterygoid braces braincase. features diagnostic of cryptodires and pleurodires 4. Within the Cryptodira two monophyletic (Late Jurassic). However, identification of pleu- taxa are recognized. In the parvorder Paracrypto- rodires in the Late Jurassic (Platychelys) and dira (consisting only of the superfamily Bae- Late Triassic (Proterochersis) suggest that the noidea) the internal carotid artery enters the pleurodire-cryptodire dichotomy took place very skull midway along the pterygoid-basisphenoid early in the history of turtles. suture, whereas in the parvorder Eucryptodira the internal carotid artery enters at the posterior end of the pterygoid. ZUSAMMENFASSUNG 5. The Eucryptodira contains three super- Die Charakteristiken der Gehirnschalenbasis families. The superfamily Chelonioidea is charac- bilden die Grundlage fur eine neue Theorie der terized by the following series of shared derived verwandtschaftlichen Beziehungen zwischen characters: sella turcica reduced or obliterated, grosseren Gruppen neuzeitlicher und ausgestor-

430 1975 GAFFNEY: TURTLE PHYLOGENY 431 bener Schildkroten. Die hier zur Entwicklung 5. Die Eucryptodira besteht aus drei Ober- phylogenetischer Hypothesen angewandte Meth- familien. Die Oberfamilie Chelonioidea ist durch ode basiert auf der Verteilung gemeinsamer, her- die folgende Reihe gemeinsamer, abgeleiteter geleiteter Eigenschaften, eine Strategie, die von Merkmale charakterisiert: sella turcica reduziert Henning (1966) und anderen erlautert wurde und oder verschwunden, dorsum sellae hoch und oft Cladismus oder Phylogenetische Systematik hangt nicht uber carotiden Offnungen, carotide genannt wird. Obwohl ich die phylogenetische Offnungen dicht nebeneinander. Die Chelonioi- Konstruktion in den Vordergrund stelle, fuhre dea umschliesst die Plesiochelyidae, Protostegi- ich auch eine neue Klassifizierung der Schildkro- dae, Toxochelyidae, Dermochlyidae und Cheloni- ten ein, welche aus streng monophyletischen idae. Das hauptsachliche gemeinsame, hergel- Gruppen (soweit ich sie bestimmen kann) besteht eitete Merkmal, welches die Oberfamilie Tri- und eine direkte Widerspiegelung der Phylogenie onychoidea bestimmt, ist die Reduzierung oder darstellt. das Fehlen der stapedialen Arterie. Die Familien 1. Die gemeinsamen, hergeleiteten Eigen- Kinosternidae, Dermatemydidae, Carettochelyi- schaften, welche fur die Gattung Testitudines dae und Trionychidae werden auf dieser Grund- kennzeichnend sind, bestehen aus: einer Schale, lage in die Trionychoidea eingereiht. Ich war Verlust der Randzahne, Hypertrophy des Mit- nicht in der Lage, die Oberfamilie Testudinoidea telohres und wahrscheinlich Akinese. unter Verwertung gemeinsamer, hergeleiteter 2. Zwei Unterabteilungen werden innerhalb Merkmale zu diagnostizieren und die Gruppe der Testudines anerkannt. Die Unterabteilung kann paraphyletisch sein, weil sie nur durch Proganochelydia besteht aus der triassischen Art primitive Grundzuge abgegrenzt ist. Die Familien Proganochelys und ist gekennzeichnet durch Testudinidae, Emydidae und Chelydridae runden uberwiegend primitive Merkmale wie eine offene die Testudinoidea aus. interpterygoide Liicke und einem seitlich geoff- Die "Amphichelydia" ist eine hohere Art, die neten Hohlraum des Mittelohres. Alle anderen sich durch primitive Gundzuge kennzeichnet und Schildkroten gehoren zu der Untergruppe Casi- angeblich die Ahnen der neuzeitlichen Schild- chelydia, welche dadurch diagnostiziert werden krote einschliesst. Die Entwicklung einer streng kann, dass gemeinsame, abgeleitete Kennzeichen monophyletischen Klassifizierung erfordert den beobachtet werden; das wichtigste Kennzeichen Ausschluss dieser Art und die Neueinstufung der sind ein geschlossener interpterygoider Hohlraum dazu geh6renden Artgruppen. und ein Mittelohr, welches eine seitliche Wand Obwohl die meisten Fossilien von Schild- aufweist. kroten nur aus Schalen oder Schalenteilen beste- 3. Die Casichelydia bestehen aus zwei unter- hen, so ist doch eine genugende Anzahl von geordneten Gruppen. Die Untergruppe Pleurodira Gruppierungen von Schadel-Schalen vorhanden, besitzt die folgenden gemeinsam, hergeleiteten um die Entwicklung einer theoretischen Merkmale: trochlea Kiefermuskel an Pterygoid, Geschichte der Gruppe zu ermoglichen. Der Quadratknochen festigt Gehirnschale. Die Unter- Erwerb einer Schale (spate triassische Periode gruppe Cryptodira weist diese gemeinsamen, her- oder fraher) ging den charakteristischen akinet- geleiteten Merkmale auf: trochlea Kiefermuskel ischen Veranderungen voraus (obwohl die Kinesis an der Ohrenkammer; Pterygoid festigt Gehirn- tatsachlich zu jener Zeit oder fruher verloren ge- schale. gangen sein mag) und der Entwicklung von Hals- 4. Innerhalb der Cryptodira werden zwei und Glieder Spezialisierungen. Anpassungen fiir monophyletische Klassen anerkannt. In der Par- die Zuruckziehung des Halses (spate cretacaische vorder Paracryptodira (die nur aus der Ober- Periode) erscheinen betrachtlich spater als die aki- familie Baenoidea besteht) tritt die innere Hals- netischen und palatoquadraten Eigenschaften, schlagader halbwegs entlang der pterygoid- welche fiir Cryptodires und Pleurodires (spate basisphenoid Naht in den Schadel ein, wahrend jurassische Periode) diagnostisch sind. Die Iden- in der Parvorder Eucryptodira die innere Hals- tifizierung von Pleurodires in der spaten juras- schlagader am hinteren Ende der Pterygoid ein- sischen Periode (Platychelys) und in der spaten tritt. triassischen Periode (Proterochersis) weist jedoch 432 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 155 darauf hin, dass die pleurodire-cryptodire Dicho- gBe MOH04HJ1eTHqeCKHe KJ1aCCCH4zKaUHH. B tomie sich sehr frulh in der Geschichte der Schild- niapBoTp.qge Paracryptodira (COCToqilneH TOJIbKO kroten volizog. H3 HaqceMeHCTBa Baenoidea) BHyTpeHH5I COHHa- apTepHR BXOAHT B qeper Ha cepewHe iBa KpIbUIOBHJHOR KOCTH H 6a3HC4)eHOHga, KPATKOE I13JI0)KEHH4E B TO BpeMq KaK B rapBoTpqIeEucryptodira Ba3HKpaHHIeCKHe IpH3HaKH cuiy)KaT OCHO- BHYTpeHH5I5 COHHa51 apTepHR BXOAHT C 3aAHeiH BOA AJIH HOBOR TeOpHH B3aHMooTHoJieHHA CTOpOHbI KpSbIJOBHAHOH KOCTH. 5. cpegiH 6oaiuuHx rpynn CoBpeMeHHbIX H BbIrlep- Eucryptodira coxlepwaT TpH HaACeMeHC- imi qeperiax. HpHMeHReMbm 3Aecb MeTOJ TBa. HaqceMeiicTBo Chelonioidea xapaKTep- mi.q pa3BHTHR 4fHnoreHeTHqecKoro rHroTe3'a H3yeTC51 cneAyioweii cepHeii o60x yHac- OCHOBaH Ha pacrpegeieHHm o6061ix yHaCiexo- fleCOBaHHbIX HpH3HaKOB: yMeHblUeHHbIM HJH BaHHbIX rIpH3HaKOB. 3To CTpaTerHH H310)KxeH 06JIHTepOBaHHbIM Type1KHM ceAJOM, BbICOKOR HpOTO- XeHHIIroM (B 1966 roqy) H qpTYHMM H 'aCTO CrIHHOi ceAna, He BbICTyrIaIOiLei Hag Ha3bIBaeTCSI K11aJH3MOM H1H 4RMoreHeTHMeC- KaMH COHHOH apTepHH, lIpOTOKaMH COHHOH KOH CHCTeMaTHKOH. XOTS rio0MepKHBaIO apTepHH paCnOIOweHbIMH TeCHO 60K 0 60K. 4HnoreHeTH'JecKyio peKOHCTpyKIgHIO, TaKwe Chelonioidea coAep)KHT Plesiochelyidae, Proto- ripeAcTaBJInso HOBYIO KiacCH4HKaHao weperiax, stegidae, Toxochelyidae, Dermochelyidae H Che- KOTopa3i COCTOHT H3 CTporo MOHO4HuieTH'eCKHX loniidae. OCHOBHbIM o6JHM yHacneqOBaHHbIM rpynni (HaCKOnbKO Mor oiipegeulHTb) H HpH3HaKOM, oipeAenSIOIHM HaACeMeHicTBo 1BfieTC5 flpHMbIM OTpaxceHHeM 4HJ1oreHeTHKH. Trionychoidea 5Bj1eTC5 yMeHbLImeHHe HuH 1. 06niHe yHacuieqoBaHHbie npH3HaKH, onpe- OTCYTCTBHe apTepH CTpeMeIKH. CeMeiicTBa AeJusniOHe OTpSIA 'epenax BKJIio'aIoT: riaHgHpb, Kinosternidae, Dermatemydidae, Carettochelyidae rIoTepso KpaeBbIx 3y6OB, rHHOTp04)HIO cpegHero H Trionychidae BKYioteHbI B HagCeMeHCTBO yxa H, IO BceH BepOSTHOCTH, aKHHe3HIo. Trionychoidea Ha 3TOM OCHOBaHHH. A1 He 2. 'IepeiraxH riogpa3AeJIOTCqqBa n1pH3HaH- cymeui oripeCeJIHTb HaJceMeiCTBo Testudinoidea HbIX no0OTpqia. Ho01oTpRi Proganochelydia IpH HOMO1H O6IHX yHacieHOBaHHbLHpH3- COCTOHT H3 po,a Proganochelys TpHacoBoro HaKOB, rpynna Mo)KeT 6bITb rapa4HieTHtec- iiepHo,na H xapaKTepH3yeTcq ripeo6Jiagaiou1HMH KOH, TaK KaK OHa pa3rpaHHqe HpHMHTHB- IpHMHTHBHbIMH OCo6eHHOCTSMM, KaK HanpH- HbIMH HpH3HaKaMH. CeMeiCTBO Testudinidae, Mep, OTKpbITOH HHTeprTepHrOH)HO IOJOC- Emydidae H Chelydridae COCTaBJ5IHOT HagceMeHc, TbIO H rioiepelHO OTKpbITOR IIOJIOCTbIO cpeq- TBO Testudinidae, Hero yxa. Bce OCTanbHbie qeperiaxH BXOJ5T Amphichelydia aBsJieTca 6ouee BbICOKOH B HOOTpIq Casichelydia, KOTOpbIH Mo)KeT TaKCOHOM, xapaKTepH3HpyeMbIM 1pHMHTHB- 6bITb onipegeuIeH fpHMeHeHHeM o6nx yiiacuie- HbIMH pHp3HaKaMH, JKO6bI Co0ep)KauM OBaHHbIX HpH3HaKOB, CaMbIM Ba)KHbIM H3 rpeAKOB COBpeMeHHbIX qepenax. Pa3bHTHe KOTOpBIX 5IB1HeTC5 3aKpbITTaf HHTepnTepHrOH- CTpOrO MOHO4HIieTheCKOH KjiaCCH)HKauH wHaq HO0OCTb H cpegHee yXo C HpHCYTCTBHeM Tpe6yeT OTpHLuaHH5 3TorO TaKCOHa H riepepac- noriepelqHoA CTeHKH. fipeJejCeHH5 TaKCHCHMe1OUIHXC5 B ero cocTaBe. 3. Casichelydia COCTOIT H3 AByX HH4¢pa- XOTS MHOFHe HCKo0laeMbIe OCTaTKH Iepenax OTp.IqOB. Pleurodira o6uagaIoT cJiegy1OL1HMH COCTOST TOJTbKO H3 naHgHpeH HJIH 4bparMeHTOB 064HMH yHacieHOBaHHbIMH1pR3HaKaMm: TpOX- iiaHiwpei, cyIeCTByeT ROCTaTOHoe KOfIHqeC- JIe.qMH Mbu1u 'ejUOCTH Ha KPBIZOBHXHOH KOCTH, TBO qepefHOnaHLHpHbIX acco0HaiwHH, pa3peiia- KBaflpaTHOR KOCTbhI, roAKpeiieHHOH K iepeii- 1OIJIHX pa3BHTHe rFHIOTeTHqeCKOH HCTOp4H rpyP- HOHI Kopo6Ke. HH4paOTpqq Cryptodira o6na- Ilbl. llpHo6peTeHIe iiaHLWps (no03AHq TpHaca iaeT CfieqyOIHMH o6IUMH HpH3HaKaMH: TpOX- HRH paHbiie) rpemecTBoBano xapaKTepHc- IIe5MH MbiiL1 qejeloCTH Ha yIIIHOH IIOJIOCTH, THEqeCKoii aKHHeTHqeCKOHi MOJ,HiHKaiLHH (XOTS KpblJIOBHUHOH KOCTbIO, irToKpeiJ1eHHOH K qe- KHHeCHC Mor B feHCTBHTeIIbHOCTH 4TbITb HOTe- penIHOH KOpO6Ke. pSIH B 3TO BpeM5 HJH paHbiie) H pa3BHTHIO 4. B HH4)paoTp5Ue Cryptodira paCII03HaIOTC5 liieiHbIX H KOHeqHOCTHbIX cneiAHajIH3aAHfH 1975 GAFFNEY: TURTLE PHYLOGENY 433

HpHcnoco6neHme K BTqrHBaHHI weH (nHo3Mii tion the use of cranial features to distinguish MeIOBbIi nepH0o,) nO1IBnqeTCH HaMHoro H03)e cryptodires and pleurodires and to determine tri- aKHHeTHqeCKHX H He6Ho-KBagpaTHoKoCTHbIX onychoid relationships. Dr. Bobb Schaeffer, nIpH3HaKoB, onpeAenqiiouHx cryptodires H Chairman and Curator of the Department of pleurodires (n03glHHk IOpCKHH nepHO0,). Og- Vertebrate Paleontology, the American Museum HaKo, OnIO3HOBaHHe pleurodires B l03AHoe of Natural History, initiated my interest in pOcCKoM nepowge (Platychelys) H TIO3AHek phylogenetic systematics and has kindly reviewed TpHace (Proterochersis) npeAnaraeT, qTO AHXOTO- the manuscript. I am particularly indebted to the MHI pleurodire-cryptodire [poH3013a otieHb following people who read the manuscript and paHO B HCTOpHHq'epenax. offered constructive comments: Dr. Richard Zweifel, Department of Herpetology, the Amer- ACKNOWLEDGMENTS ican Museum of Natural History; Dr. Niles El- dredge, Department of Fossil and Living Inverte- The present paper would not have been possi- brates, the American Museum of Natural History. ble without the, generosity of Dr. Samuel B. Dr. Thomas Parsons, University of Toronto, lent McDowell of Rutgers University. Dr. McDowell me a large collection of sectioned turtle heads for allowed me free access to a number of his un- which I am grateful. The fine quality of the illus- published manuscripts, which are the source for trations is attributable to the talents of Ms. Lor- many of the ideas I present here. I also thank raine Meeker and Mr. Chester Tarka, Department him for his critical reading of the manuscript. of Vertebrate Paleontology, the American Mu- Although we may differ in methodology and seum of Natural History. interpretation, he originally brought to my atten-

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