THE PHYLOGENETIC RELATIONSHIPS of SOFT-SHELLED TURTLES (FAMILY Trionychidae)

Home , Apalone, Cyclanorbinae, Kallokibotion, Lissemys, Paracryptodira, Pelochelys

THE PHYLOGENETIC RELATIONSHIPS OF SOFT-SHELLED TURTLES (FAMILY TRIONYCHiDAE)

PETER ANDRE MEYLAN

BULLETIN OF THE

AMIERICAN.MUSEUM OF NATURAL HISTORY.i VOLUME~1,86: ARTICLE 1. NEW YORK:0 1987 Recent issues of the Bulletin may be purchased from the Museum. Lists of back issues of the Bulletin, Novitates, and Anthropological Papers published during the last five years are avatlable fiee of charge. Address orders to: American Museum of Natural History Library, Department D, Central Park West at 79th St., New York, New York 10024. i THE PHYLOGENETIC RELATIONSHIPS OF SOFT-SHELLED TURTLES (FAMILY TRIONYCHIDAE)

PETER ANDRE MEYLAN Thorne Fellow Department of Vertebrate Paleontology American Museum of Natural History

BULLETIN OF THE AMERICAN MUSEUM OF NATURAL HISTORY Volume 186, article 1, pages 1-101, figures 1-34, tables 1-22 Issued June 26, 1987 Price: $9.00 a copy

Copyright © American Museum of Natural History 1987 ISSN 0003-0090 CONTENTS Abstract ...... 4 Introduction ...... 4 Methods ...... 7 The Phylogenetic Method ...... 7 Basic Taxa ...... 10 Terminology ...... 10 Results ...... I 1 Variation in Shell Morphology ...... 11 Carapace Size and Shape ...... 13 Nuchal Region ...... 15 The Neural Series ...... 19 Shell Periphery ...... 21 Posterior End of Carapace ...... 23 Plastron ...... 23 Variation in SkuH Morphology ...... 26 Nasal Region ...... 27 Orbital Region ...... 29 Skull Emargination ...... 29 Stapedial Foramen ...... 34 Processus Trochlearis Oticum and Quadrate ...... 34 Trigeminal Region ...... 37 Occipital Region ...... 38 Palate ...... 40 Variation in the Visceral Skeleton and Nonshell Postcrania ...... 43 Mandible ...... 43 Hyoid ...... 46 Cervical and Body Vertebrae ...... 48 Pelvis ...... 50 Pectoral Girdle ...... 53 Appendicular Skeleton ...... 53 Discussion ...... 54 Higher Relationships of the Trionychidae ...... 54 Monophyly of the Trionychoidea ...... 54 Monophyly of the Kinostemidae, Carettochelyidae, and Trionychidae ...... 58 Monophyly of the Staurotypinae, Carettochelyidae, and Trionychidae ...... 61 Monophyly of the Carettochelyidae and the Trionychidae ...... 61 Monophyly of the Trionychidae ...... 62 Relationships Among the Recent Trionychidae ...... 62 Evidence from Shell Morphology ...... 63 Evidence from Skull Morphology ...... 65 Evidence from Nonshell Postcrania and Lower Jaw ...... 69 Formulation of a General Hypothesis of Relationships for the Trionychidae ...... 69

2 Comparison of Results to the Prevailing Hypotheses of Trionychid Relationships ...... 74...... 74 Trends and Mechanisms in Soft-Shelled Turtle Evolution ...... 78 Classification of the Living Trionychidae ...... 88 Acknowledgments ...... 94 Appendix 1. Specimens Examined ...... 95 Literature Cited ...... 96

3 ABSTRACT Phylogenetic analysis of 113 characters of the ticus, T. swinhoei, T. ferox, T. spiniferus, and T. osteology of the 22 living species of trionychid muticus, and can be recognized by the presence of turtles and representatives of all other living turtle eight or fewer neurals (first and second are fused), families, provides abundant evidence on the re- deeply emarginate prefrontals, and a large contri- lationships of soft-shelled turtles to other turtles bution by the parietal to the processus trochlearis and on the interrelationships within the family. oticum. The Indian group includes four species: These data suggest that the family Trionychidae T. gangeticus, T. hurum, T. leithii, and T. ni- shares a unique common ancestor with the Der- gricans; all exhibit a free first neural, five plastral matemydidae, Kinosternidae, and Carettochelyi- callosities, and intermediately extended epiplas- dae, and that the Kinosternidae share a unique tra. Lastly, the T. steindachneri group, which in- common ancestor with the Trionychidae and Ca- cludes T. steindachneri, T. sinensis, and T. sub- rettochelyidae. Furthermore, it appears that the planus, is diagnosed by a descending spine of the staurotypine kinosternids are most closely related opisthotic that divides the fenestra postotica in to the Trionychidae and Carettochelyidae. Ca- most specimens. rettochelyids and trionychids share numerous Two equally parsimonious arrangements of the unique features and clearly constitute a mono- Trionychinae differ in the placement of the North phyletic group. American clade. In one, this clade is the sister Within the Trionychidae, the subfamilies Cyc- group of the T. cartilagineus clade; in the other, it lanorbinae and Trionychinae are recognized as is the sister group of the T. steindachneri clade. In monophyletic clades. Recognition of three cyclan- both, the Indian group is paraphyletic and gives orbine genera, Cycloderma, Cyclanorbis, and rise to the T. steindachneri clade. Lissemys, is warranted. Within the Trionychinae, A revised classification of the family Trionych- four distinct clades are recognized. The Trionyx idae is provided. The use of 2 subfamilies, 6 tribes, cartilagineus group includes Chitra indica and Pe- and 14 genera is recommended. This expanded lochelys bibroni, on the basis ofthe unique location taxonomy will more completely reflect the hier- of the foramen posterior canalis carotici interni, archical relationships that reflect recency of com- and features of the trigeminal region. The North mon ancestry as determined by the cladistic anal- American group includes T. triunguis, T. euphra- yses.

INTRODUCTION Within recent years a fundamental revision summarized by Gaffney (1984). The largest of the systematic relationships of turtles has remaining family for which a complete cla- begun. This revision was precipitated by distic study does not exist is that comprising Gaffhiey (1975), who presented a reorgani- the soft-shelled turtles, the Trionychidae. zation of the Testudines using the cladistic This gap is significant, considering the large method (as outlined in Gaffney, 1979a; Wi- size, abundance, and great age of the family. ley, 1981). Other authors have followed Gaff- The Trionychidae includes more than 250 ney's lead in applying this method to prob- named species (ca. 230 fossil and 22 extant) lems in chelonian systematics, resulting in a and occurs on every continent except Ant- much clearer understanding of the phyloge- arctica. It is a very old family, with definite netic relationships among turtle taxa. Con- representatives from the Cretaceous (Romer, cise hypotheses of the relationships within 1956). Representation of this family in the most families are now available (Progano- fossil record is considerable, although diffi- chelyidae, Gaffniey and Meeker, 1983; Chel- cult to document because few authors treat idae, Gaffihey, 1977; Baenidae, Gaffney, 1972; the fossils of this troublesome group. The best Meiolaniidae, Gaffhey, 1983; Chelonioidea, evidence of its ubiquity is reported by Gaffhey, 1976; Kinosternidae, Hutchison and Hutchison (1982), who showed that the Bramble, 1981; Trionychidae [shell only], Trionychidae has the most continuous record Meylan, 1985; Emydidae, Hirayama, 1985; of 11 reptile families examined from the Ce- Testudinidae, Crumly, 1982, 1985) and are nozoic of western North America. 4 1 987 MEYLAN: TRIONYCHIDAE 5

Although authors do not agree on the re- and other osteological characters and has been lationships of trionychids to other turtles, I followed by Romer (1956), Pritchard (1967, have never seen a single reference doubting 1979a, 1979b), Mlynarski (1976), and others. the monophyly of the family. It is so dis- Karyotypic data have recently been cited tinctive that some authors have placed the which partially support this arrangement family in a separate suborder equivalent to (Bickham and Carr, 1983). It is obvious from the Cryptodira and Pleurodira (Boulenger, these various arguments that the phyloge- 1889; Siebenrock, 1909; Bergounioux, 1932, netic position of the family Trionychidae 1955), an arrangement for which Loveridge within the Testudines is still in question. and Williams (1957) found some support. A narrower but equally urgent problem Modem morphologists argue that this family concerns the interrelationships within the is a group of aberrant cryptodires allied to family Trionychidae. The lack of resolution the Carettochelyidae, Dermatemydidae, and of relationships within the family is indicated Kinosternidae (McDowell, 1961; Albrecht, by the current placement of nearly all species 1967; Zug, 1971; Gaffhiey, 1975, 1984). But (ca. 235) in a single "wastebasket" genus, Tri- others disagree, arguing that on the basis of onyx. For more than 50 years since the major karyology the Trionychidae, along with the revision by Hummel (1929), there has been Carettochelyidae, is the sister group of all a strong tendency to synonymize trionychine other cryptodires (Bickham et al., 1983). On genera (except Chitra and Pelochelys) with the basis of serological tests, Frair (1 9 8 3) sup- Trionyx (Bergounioux, 1955; Romer, 1956; ported the placement of the family in its own Huene, 1956), with the result that 47 generic suborder. names are now considered synonyms (Smith Among those workers willing to place the and Smith, 1980). The apparent reason for Trionychidae among the Cryptodira, there is this is not uniformity of morphology, but difference of opinion as to which cryptodire rather an absence of a complete and system- families are the closest relatives of soft-shelled atic interpretation ofthe characters. The large turtles. Since its discovery, Carettochelys number of taxa and high intraspecific vari- Ramsay (1886) has been considered closely ability in the shape and degree of ossification related to the Trionychidae, although some of both the shell and skull make any study authors were confused by false reports of of trionychid relationships using a phenetic mesoplastra in this genus (Boulenger, 1889; method extremely difficult. The most im- Pritchard, 1967). Among the authors who portant recent studies are those of Loveridge have recognized close relationship between and Williams (1957) and De Broin (1977). Carettochelys and the Trionychidae (Boulen- On the basis of osteological characters, color ger, 1889; Baur, 1890, 1891b; Waite, 1905; pattern, and geography, Loveridge and Wil- Siebenrock, 1902, 1913), some have rec- liams arrived at the arrangement redrawn as ommended that superfamilial status be rec- figure 1. The De Broin (1977) arrangement ognized (Trionychia, Hummel, 1929; Tri- is based largely on characters of the shell and onychoidea, Walther, 1922). skull (especially the palate), but is given in Several morphologists (Baur, 1891a; Mc- insufficient detail to allow construction of a Dowell, 196 1; Albrecht, 1967; Zug, 197 1; and branching diagram. Both the Loveridge and Gaffney, 1975, 1984) have allied the Trion- Williams (1957) and De Broin (1977) ar- ychidae and Carettochelyidae with the Der- rangements contain features which appear in matemydidae and the Kinostemidae. Gaff- a cladistic analysis of the family based on ney (1975) applied the name Trionychoidea shell morphology (Meylan, 1985). to this group. This enlarged concept of the Phylogenetic analysis provides a method- Trionychoidea is in clear conflict with the ological breakthrough that has allowed elu- frequent association ofthe Kinosternidae with cidation of trionychid relationships. This the Chelydridae and the inclusion of these method results in arrangements of taxa in two families in a clade with the Emydidae hierarchies of internested natural groups. Be- and Testudinidae. This latter arrangement cause uniquely derived character states are was proposed by Williams (1950) and is based used only from that point in the hierarchy on the morphology of the cervical vertebrae beyond which they are shared by all taxa, 6 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 186

Fig. 1. A cladogram for the Trionychidae based on figure 50 in Loveridge and Williams (1957). rrionyx emoryi, which appears in the Loveridge and Williams figure, is currently considered to be a synonym of T. spiniferus (Webb, 1962) and is not included in the cladogram. these states automatically form diagnoses. representatives of the entire order. With its Recognition of the diagnostic features of scope expanded by the requirements of phy- monophyletic groups produces a strong hy- logenetic methodology, this study has pro- pothesis for the proper position of the Tri- duced significant data on the distribution of onychidae among the Testudines and clarifies character states among all turtles. These data the interrelationships of its living species. In are valuable in assessing the interfamilial re- this work I have developed a hypothesis of lationships of trionychids. cladistic relationships for the 22 Recent The methodology employed also provides species of the family Trionychidae. The a means for identifying those characters which availability of large series of most living have states that appear to have been gained species and the completeness ofRecent spec- or lost independently, or which may have imens has allowed a more complete character undergone reversal. These events, termed ho- analysis than could be developed from fossils moplasy, are the single most confounding alone. A complete revision of the fossil mem- feature in systematics. When systematic eval- bers of the family lies beyond the scope of uations must be made from limited data sets, this study and will take many years to com- as in paleontology, it is important that char- plete. acters subject to homoplasy are identified. One of the most laudable aspects of phy- Because most fossil Trionychidae have been logenetic analysis, which is absent from phe- described from shell material, an analysis of netic methods, is that it requires an observer homoplasy in shell characters is critical to to look beyond the taxa of immediate inter- future work on the systematics of fossil forms. est. Decisions about the polarity of character The descriptive portions ofthis study focus change in the ingroup (the Trionychidae) re- entirely on characters significant in produc- quires information from related forms. ing a phylogenetic arrangement for the in- Therefore this study of the relationships of group. They are not meant as an exhaustive the members of a single family includes an description of the osteology of the Tri- investigation of interfamilial relationships onychidae. Such a study has long been avail- and consequently has evolved into a study of able (Ogushi, 191 1). 1987 8MEYLAN: TRIONYCHIDAE 7

The primary objectives of this project are resolving relationships among the 22 extant to fill the largest remaining gap in our un- trionychid species. In addition, this study will derstanding of the phylogeny of living turtles help provide a basis for future analysis of the by (1) determining the best placement of the relationships among the approximately 230 Trionychidae within the Testudines; and (2) species known only from fossil material.

METHODS THE PHYLOGENETIC METHOD relationship using the shared derived char- (parsimoni- Systematics is not only a means of provid- acter data in the most efficient ing names for organisms and groups of or- ous) manner. ganisms, but also a method by which we can STATES infer and express the historical data of their HARACTERS AND CHARACTER descent. Biologists agree that all organisms The systematics of soft-shelled turtles has have evolved by a single phylogenetic pro- been based almost exclusively on skeletal gression. The actual pedigree of taxa repre- morphology (see for example Baur, 1893; sents a succession of shared ancestries. Anal- Siebenrock, 1902; Hummel, 1929; Stejneger, ysis of common ancestry can be a powerful 1944; Loveridge and Williams, 1957; De explanatory tool for the distribution of traits Broin, 1977). Characters of the external soft of functional morphology (Lauder, 1982), anatomy are oflittle use, and few studies have ecology (Stearns, 1984), physiology (McNab, employed them. The exceptions are the use 1978), and behavior (Meylan and Auffen- of color pattern (Loveridge and Williams, berg, 1986). But the possibility that any fea- 1957; Webb, 1962) and the presence of fem- tures are a result of shared common ancestry oral and caudal valves in the Cyclanorbinae rather than more proximal causes cannot be (most studies). For this reason, the character explored unless classification reflects this sin- survey in the present study was restricted to gle phylogenetic progression. Consequently, skeletal morphology. A secondary advantage it is critical for systematists to propose clas- of this emphasis is future direct application sifications which reflect shared common an- of this study to the interpretation of the re- cestries. The cladistic method is explicit in lationships of fossil trionychid species. its reliance on shared derived characters, Characters of two types were sought: those which are a function ofthe descent of species. uniform within the family but varying among The phylogenetic method relies on the higher taxa outside the family; and those identification and use of shared derived char- varying among different groups of trionychid acters to discover recency of common ances- species. The former (interfamilial characters) try. Given that parallelism is the exception provide a data set for hypotheses on the rather than the rule, any two taxa are more placement of trionychids within the Testu- likely to have a shared trait because it was dines. The latter (intrafamilial characters) present in their common ancestor rather than provide a basis for developing phylogenetic because it appeared independently on two oc- hypotheses for species within the family casions. Thus the distribution of shared de- Trionychidae. rived characters among taxa can be used to Variation in a given character is treated as build a hierarchical ranking of recency of states of that character. Many of the char- common ancestry. acters used have only two states, such as pres- Developing this hierarchical ranking re- ence or absence of a given bone, structure, or quires (1) identification ofcharacters with ap- contact. Other characters include three or propriately distributed character states; (2) more discrete states or continuous variation. identification of primitive versus derived Multistate and continuous characters pose states for the characters; and (3) a system for two methodological problems. First, for pur- the formulation of hypotheses of hierarchical poses of analysis it is necessary to divide a 8 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 186

LENGTH INTERMAXILLARY FORAMEN / LENGTH PRIMARY PALATE 0~~~~~ mo a c PaUJlc O 0zx0 e

C, 0 2G0cc m g zu x 4c0UaIO L z *uIow. .. 0 I .10 .20 .30 .40 .5o .60 .70 .02 .03 .04 .05 .06 .07 .08 .09 .10 .11 .12 .13 .14 .15 0 o~~ Z~~~~~~z D LSL I cs , E w cI3 II 3 0~~0 p z~~~~~ccr IU0coI Ul LENGTH PRIMARY PALATE / TOTAL SKULL LENGTH Fig. 2. Comparison of two continuous characters examined during the course ofstudy ofthe variation in size of the foramen intermaxillaris. Foramen intermaxillaris/length primary palate falls into five discrete classes and is used in the cladistic analysis. Foramen intermaxillaris/total skull length shows no such discrete classes and could not be used.

continuously varying character into a num- just as the number of postulated changes in ber of discrete states. Secondly, it has been a clade are ordinarily minimized by phylo- proposed (Gaffihey, 1 979a, personal com- genetic systematics. For example, we could mun.) that recognition of intermediate states propose that extreme reduction of peripheral requires ad hoc hypotheses that evolution has bones in Lissemys occurs independently of occurred in certain ways, and therefore mul- complete loss of peripheral bones in all other tistate characters should be avoided. trionychids (two steps) or that reduction in Information contained in multistate char- Lissemys is followed by complete loss in oth- acters, or morphoclines, is extremely useful er trionychids (also two But these for steps). two understanding the history of descent of two-step changes are not equivalent. One re- any group (Maslin, 1952) and has been crit- quires two complete changes from an appar- ical in formulating a hypothesis of relation- ently very fixed primitive condition (loss of ships for trionychids based on the shell alone peripheral bones occurs otherwise only in (Meylan, 1985). The multistate characters that Dermochelys); the other requires a single di- have been used in the present study are of vergence from the primitive condition which three types: (1) continuous characters of is subsequently elaborated. shape, size, relative position, etc., for which Multistate discrete characters (e.g., number states have been determined by the occur- of peripherals or neurals) present little prob- rence of natural breaks along a continuum; lem for the recognition of different character (2) discrete characters of a meristic nature for states. Continuous characters of relative size which more than two possible states exist; must be divided into states and by some artificial (3) two-state characters in which both but objective means. As in other studies (Marx states frequently occur in the same species, and Rabb, 1972; Drewes, 1984), I have di- requiring the recognition of that third, inter- vided continuous characters plotting the mediate condition. I by submit that in all of these average values for terminal taxa along a con- cases, as for two-state characters, only a hy- tinuum, and employing natural breaks in dis- pothesis ofcharacter polarity is necessary. By tribution as evidence of various character invoking the principle of parsimony we can states (see fig. 2, for example). If no natural suggest that the degree of change required to breaks in distribution occurred, the character arrive at a given state should be minimized, was discarded. 1987 MEYLAN: TRIONYCHIDAE 9

The characters employed in this study are given equal weight. Certain authors, most no- CHARACTER POLARITY tably Hecht and Edwards (1977), have argued Once the states of a given character have that some types of characters, for example been recognized, it is essential to identify the those involving loss, should be given little primitive and derived extremes, or character weight. In this study characters are weighted polarity. Numerous criteria for determining only in the sense that they have been included the polarity ofcharacter transformations have or discarded, depending on the distribution been offered in the literature. The most often of variation. I disagree with the concept of a treated are outgroup comparison, common- priori character weighting in general, and in ality, evidence from the fossil record, evi- particular, I do not accept the supposition of dence from embryology, and correlation of Hecht and Edwards that characters involving character states (Kluge and Farris, 1969; Marx loss are necessarily simple and subject to ho- and Rabb, 1972; Wiley, 1981). I follow Gaff- moplasy, and therefore should be given low ney (1979a), Watrous and Wheeler (1981), weight. The loss of a major structure such as and Wiley (1981) in relying on outgroup com- the peripheral bones in turtles or the neural parison as the best criterion for character po- spine in snake vertebrae (a character oflowest larity decisions. This criterion has been dis- value in the Hecht and Edwards' scheme) can cussed at some length in recent systematic occur only when a complex structural alter- literature and methods have been outlined native (a character of highest value in the for making the most efficient use ofoutgroups Hecht and Edwards' scheme) is available. The when they are well established (global par- losses mentioned above require the devel- simony, Maddison et al., 1984), or when a opment of strong and deeply sutured rib heads number ofoutgroups could be the sister taxon in the case of certain trionychoids, and re- to the ingroup (outgroup substitution, Don- location of numerous muscles that originate oghue and Cantino, 1984). or insert on the neural spine in snakes. This In this study I have employed data from may explain why complete loss of each of all families of turtles and the arrangement of these features has apparently occurred only Gaffney (1984) to make use of the concept of once. In both instances, loss is the immedi- global parsimony. That is to say, the out- ately apparent result of a complex evolution- group for the Trionychidae is all other turtles. ary event, and therefore should not be dis- Decisions concerning polarity of characters counted. within this family are most directly affected There are two reasons for the inclusion of by the distribution of states within the Trion- a maximum number of characters in this ychoidea. The concept of the Trionychoidea analysis. First, such inclusiveness is neces- is based on characters polarized at a higher sary to provide results that will be of greatest level of universality. value to paleontology. Paleontologists are often faced with solving systematic problems on the basis of incomplete material. By in- FORMULATION OF PHYLOGENETIC creasing the number of characters, there is an HYPOTHESES increased likelihood that characters present In my provisional arrangement of the Re- in any given fossil will have been studied. cent species of the Trionychidae based on 16 The second reason is to provide three sepa- characters of shell morphology (Meylan, rate data sets to test the monophyly of prob- 1985), I conducted the search for the most lematic groups and detect homoplastic char- parsimonious cladogram (that requiring the acter states. fewest evolutionary steps) by hand. As ad- Because there are 1 3 characters discussed ditional data have been assembled for this in this paper, some means of assisting the study I have partitioned them into three sets reader is required. Therefore, the characters (shell, skull, and visceral skeleton plus non- are numbered. Characters 1-30 pertain to the shell postcrania). As each of these data sets shell, 31-78 pertain to the skull, and 78-113 became very large, it became necessary to pertain to the visceral skeleton and nonshell employ a computer program to generate postcrania. cladograms. I used Phylogenetic Analysis Us- 10 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 186 ing Parsimony (PAUP, version 2.3, 1984) by Chinese species which these authors had rel- D. Swofford, which was made available egated to the synonymy of Trionyx sinensis through the Northeast Regional Data Center (De Broin, 1977; Meylan and Webb, 1987) at the University of Florida. and the relegation of Trionyx ater to subspe- PAUP emphasizes simple unrestricted cific level within T. spiniferus (Smith and parsimony procedures (Swofford, 1984). Its Smith, 1980). The 22 species used are the author finds that there is close correspon- same as those employed in Loveridge and dence between results obtained by hand and Williams (1957). those generated via PAUP. One advantage Two species recognized since the publica- in addition to the time-saving capabilities of tion of Wermuth and Mertens (1961) have PAUP is the MLULPARS option. This option been deemed insufficiently distinct to be used results in a listing of all "most parsimonious" in the current study. On the basis of the ab- trees. It seems certain that when working by sence of integradation between Lissemys scu- hand one is unlikely to discover all such trees. tata and L. punctata, Webb (1982) proposed The ability of the program to handle missing that the former be considered a full species values improved its utility for use in the cur- rather than a subspecies of L. punctata (An- rent project. nandale, 1912; Deraniyagala, 1939; Wer- I have employed PAUP to formulate the muth and Mertens, 196 1). The primary mor- most parsimonious hypothesis of relation- phological differences between the two are ship for the species within the family Tri- the configuration of the peripherals and the onychidae that can be derived from each of early development of plastral callosities in L. the three independent sets ofosteological data. scutata. All superficial dermal callosities are These are (1) 22 characters of the shell (an highly variable within trionychid species, and expanded version of Meylan, 1985); (2) 23 thus additional, less variable features should characters of the skull; and (3) 13 characters be found to corroborate the validity of L. of the lower jaw and postcrania (exclusive of scutata before it is considered a distinct the shell). Additionally, an analysis of the species. If L. scutata is distinct, there is little three data sets combined was performed. doubt that L. punctata is its closest relative. The name Trionyx nakornsrithammara- COMPARISON oF FUNDAMENTAL jensis was proposed for a "rare softshell" from HYPOTHESES AND FORMULATIoN OF A Thailand (Wirot, 1979). Judging from the GENERAL HypoTHEsIs color pattern of the specimen in the figure included with the description, this name ap- Following the development of cladograms plies to Trionyx cartilagineus. from the three separate data sets, it was de- sirable to formulate a single general cladogram from them and to compare the utility TERMINOLOGY of various characters, especially those of the TAXONOMY shell, in the formulation of this general hypothesis. Two methods, analysis Existing generic assignments are used for of the three trionychids data sets in combination and a stepwise con- throughout the results and dis- sideration ofcompatible characters, have been cussion sections ofthis paper. However, since used for this procedure. Neither the Nelson the generic name Trionyx is currently used (1979) method nor the similar Adams (1972) with about three-fourths of the species, little method produced a single, well-resolved information is conveyed by the use ofgeneric cladogram of trionychid relationships. names. Therefore, specific epithets are used alone in figures and tables throughout. BASIC TAXA Certain collective terms are used provi- sionally for groups of trionychid species The species of living trionychid turtles rec- throughout the text. They are used for groups ognized for this study are essentially those which have been suggested to be monophy- listed by Wermuth and Mertens (1961). The letic by more than one author. The Cycla- only differences are the use of the name Tri- norbinae (Cyclanorbidae of Deraniyagala, onyx swinhoei for the large and colorful 1939; or Lissemydinae, of Williams, 1950) 1987 MEYLAN: TRIONYCHIDAE 1 1 includes Cyclanorbis elegans, Cyclanorbis MORPHOLOGY senegalensis, Cycloderma aubryi, Cycloder- ma frenatum, and Lissemys punctata. These Terminology for elements of the carapace species are considered to constitute a natural and plastron follows Loveridge and Williams group in treatments by Deraniyagala (1939), (1957). The concepts of Williams and Loveridge and Williams (1957), and Meylan McDowell (1952) concerning the homologies (1985). The sister group of the Cyclanorbinae of the elements of the anterior lobe of the is the plastron are rejected. These authors suggest Trionychinae, which includes all non- that the anterior midline element in triony- cyclanorbine members of the family. There chids is not the is good evidence that the Trionychinae is a entoplastron, but rather a monophyletic group (Meylan, 1985). It has fused pair of epiplastra, and that the ante- been recognized as such by Deraniyagala riormost paired elements are neomorphs (1939), and Loveridge and Williams (1957). which they term preplastra. On the basis of Within the Trionychinae two species groups the sites oforigin and insertion ofthe anterior have been treated as natural in all recent ac- trunk musculature, Bramble and Carr (Ms) counts: the four species of the Indian sub- have shown that this is incorrect and that the continent (Trionyx gangeticus, T. leithil, T. anterior plastral elements in trionychids cor- hurum, and T. nigricans); and the three North respond to those of other turtles. The midline American forms (T. ferox, T. muticus, and element is the entoplastron, and the ante- T. spiniferus) (Loveridge and Williams, 1957; riormost pair are the epiplastra. For skull and De Broin, 1977; Meylan, 1985). lower jaw terminology, I follow Gaffhey Names of familial and higher taxa of the (1972, 1979b), who has developed his glos- Testudines are those suggested by Gaffney sary of skull morphology in part from Par- (1984). Monophyly of these taxa is not reex- sons and Williams (1961). A variety ofsources amined except for the superfamily Triony- is used for the nonshell postcrania: Williams choidea and its member families. The suffixes (1950) for cervical vertebrae; Baur (1891a) -oidea for superfamilies, -idae for families, and Zug (1971) for the pelvic girdle; and and -inae for subfamilies are used consis- Schumacher (1973) for the hyoid. tently throughout the Testudines.

RESULTS VARIATION IN SHELL MORPHOLOGY in the Trionychidae and Dermochelyidae is Thirty characters of the carapace and plas- composed of epithecal ossifications of more tron have been determined to be useful for superficial origin than the dermal ossifica- establishing inter- and/or intrafamilial relations considered to form the shell in other tionships of trionychid turtles (table 1). They turtles. This implies that the superficial layer pertain to carapace size and shape, the nuchal ofthe shells of members ofthese two families region, the neural series, the shell periphery, are not strictly homologous to the same layer posterior end of the carapace, and the plas- in other turtles. The existence of a nonho- tron. Because ofthe unique nature ofthe shell mologous superficial layer seems quite pos- of trionychids few ofthese characters are use- sible for Dermochelys in which there is total ful in testing proposed interfamilial relation- independence of the superficial bone and the ships. deeper dermal elements of the shell (i.e., the All character polarities discussed in this ribs and neural spines of vertebrae). In cross section are based on outgroup comparisons. section these "epithecal bones," which make It is therefore important that doubts about up the superficial bony mosaic, lack dense the homology of the shell of trionychids to layers on the external and internal surfaces that of other turtles be considered. Zangerl (fig. 3, bottom). Thus they do not fit Zangerl's (1 9 6 9) contended that the external bony layer (1969) description of turtle shell bone of typ- 12 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 186

TABLE 1 TABLE 1-(Continued) Shell Characters and Character States Used for Resolving Phylogenetic Relationships of Recent Characters Character states Trionychid Turtles. For each character the most primitive state is 16. pleurals which meet at 1. eighth only number 1 midline 2. seventh and eighth or eighth only Characters Character states 3. sixth, seventh, and eighth or seventh 1. width/length of nuchal 1. less than 2 and eighth bone 2. greater than 2 4. more than sixth, 3. greater than 3 seventh, and eighth 4. greater than 4 0. none 2. anterior and posterior 1. no 17. point of reversal of ori- 1. at neural eight costiform processes of 2. yes entation of neurals 2. at neural seven nuchal bone united 3. at neural six or sev- 3. position of anterior edge 1. posterior edge of en of first body vertebra nuchal 4. at neural six relative to nuchal bone 2. middle of nuchal 5. at neural four, five, 3. anterior edge of nu- or six chal 18. suprascapular fonta- 1. closed at hatching 4. first and second neurals 1. no nelles 2. closed in large fused 2. yes adults only 5. total number of periph- 1. 22 3. open throughout erals 2. 20 life 3. 14-18 19. epiplastron shape 1. J-shaped 4. 0 2. I-shaped 6. peripherals sutured to 1. yes 20. length epiplastra ante- 1. short pleurals 2. no rior to entoplastron 2. intermediate 7. prenuchal bone 1. absent contact 3. long 2. present 21. depressions on eighth 1. present 8. size of eighth pleurals 1. large pleurals for contact of 2. absent 2. reduced or absent ilia 9. number of plastral cal- 1. seven 22. shape of entoplastron 1. anterioposteriorly losities 2. five elongate or round 3. four 2. "boomerang- 4. two shaped" 5. none 23. bridge length 1. long 0. nine 2. short 10. hyoplastra and hypo- 1. no 24. largest adult size 200 1. no plastra fuse just after 2. yes mm or less (disc length) 2. yes hatching 25. carapace margin straight 1. no 11. hyoplastra and hypo- 1. no to concave posteriola- 2. yes plastra fuse in adults 2. yes terally 12. fusion of xiphiplastra 1. absent 26. plastral buttresses reach 1. both axillary and 2. present across peripherals to inguinal 13. hypo-xiphiplastral 1. xiphiplastra lateral contact pleurals 2. axillary only union to hypoplastra 3. neither 2. hypoplastra lateral 27. carapace sutured to 1. yes to xiphiplastra plastron all across 2. no 14. number of neurals 1. nine bridge (fused 1 and 2 counted 2. eight or nine 28. rib heads strongly su- 1. no as 2) 3. eight tured to vertebral centra yes 4. seven or eight 29. sexual dimorphism in 1. no 5. seven or fewer disc length 2. yes 15. variability in position of 1. always at same 30. shell sculptured and 1. no neural reversal neural lacking epidermal scutes 2. yes 2. always at adjacent neurals 3. highly variable 1987 MEYLAN: TRIONYCHIDAE 13

Fig. 3. Cross sections of single pleural elements of three cryptodiran turtles. Top, Chrysemys picta (UF 40615); middle, Trionyxferox (UF 54212); bottom, Dermochelys coriacea (UF 37557). ical dermal origin. The case is less clear for the most superficial bony layer in the Tri- CARAPACE SIZE AND SHAPE onychidae. In members of this family, as in Even the smallest fragment of trionychid other turtles, there is complete correspon- shell is immediately recognizable by its char- dence between superficial bony elements and acteristic sculpturing. This sculpturing is nev- underlying deep dermal elements of the car- er divided by scute sulci because scute sulci apace. Furthermore, cross sections of either and the epidermal scutes they delineate, which carapacial or plastral elements of trionychids are present on the shells ofmost other turtles, reveal the presence ofa spongy middle region are always absent in tnionychids. The only with compact lamellar layers on either side other living turtle which has a sculptured shell (fig. 3 top, middle). This agrees with Zangerl's and lacks epidermal scutes is Carettochelys. own description of typical dermal shell bone The absence of epidermal scutes is consid- and fits Suzuki's (1963) description of the ered to be a derived condition (character 30, results of development of dermal shell bone table 8). in Pseudemys scripta. Zangerl's (1939) orig- Recent trionychids are, for the most part, inal argument for an epithecal origin of the large turtles and many species approach one superficial bone in trionychids is based on its meter in total carapace length. The carapace delayed development rather than on its site consists of a bony disc with cartilaginous of origin. The late development of the su- margins. In discussions of osteological ma- perficial layer does not have any clear bearing terial, including this one, it is the bony disc on the homology of its origin, and must yield length rather than total carapace length which to the physical evidence that, in cross section, is used as an index of total size. The largest trionychid shell elements do not differ sig- species of trionychids have bony discs over nificantly from other sectioned chelonian 500 mm in length; most reach disc lengths shells which are considered to be of normal of 300 mm (table 2). The exceptions are few, dermal origin. Thus, unless other evidence and these are usually 200 mm or less in disc can be provided, the superficial elements of length. trionychid shells may be regarded as homol- Five species of Trionyx are small (under ogous to those of other turtles. 200 mm disc length): Trionyx muticus, T. 14 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 186

TABLE 2 Among other trionychoids, small size is Maximum Size of Recent Trionychids common only in the Kinosternidae. Most (Character 24) known species of the Dermatemydidae and Carettochelyidae reach bony carapace lengths of 400-500 mm. Among the Kinostemidae the genus Staurotypus reaches adult sizes close Species Specimen (mm) to those of Dermatemys and Carettochelys; whereas Claudius, Kinosternon, and Ster- aubryi BMNH 61.7.29 365 notherus are smaller, usually under 200 mm. bibroni BMNH 80.4.25.6 415 is cartilagineus ZSM 832/1920 316 It seems likely that reduction in total size elegans NMW 1437 475 a derived condition common to the Kino- euphraticus cited in Siebenrock, 1913 282 sterninae and that similar diminution oc- ferox UF 45341a 371 curred independently in one or more groups formosus cited in Annandale, 1912 274 within the Trionychidae. Thus, small cara- frenatum BMNH (Type of 535 pace size is considered to be a derived con- Aspidochelys dition among trionychids (character 24, table livingstonz) 3). gangeticus cited in Annandale, 1912 485 Sexual dimorphism in total size is well hurum cited in Annandale, 1912 416 the male indica MNHNP 1880-182 550 known for turtles. In certain forms leithii EOM 2819 380 is larger and in others the female is larger. muticus UMMZ 128086 124 The latter occurs most frequently among nigricans cited in Annandale, 1912 403 aquatic emydids but also occurs in some punctata cited in Deraniyagala, 370 trionychids. Webb (1962) provides data which 1939 indicate that all three North American forms senegalensis BMNH 1949.1.3.51 325 are sexually dimorphic in size. This has not sinensis ZSM 429/1911 201 been shown for any Old World forms with spiniferus UF 37228 186.5 the possible exception of Chitra indica (Wirot, steindachneri MNHNP unnumbered 170 1979). Because of apparent absence among subplanus calculated from skull ca. 250 BMNH 81.10.10.12 other trionychoids, sexual dimorphism, in swinhoei calculated from fig. lA, 490 which the female is larger, can be considered Heude, 1880 a derived feature within the Trionychidae riunguis KNM-VP-ER-8123 410 (character 28, table 3). The carapace of trionychids is unique a,Allen (1982) reported an apparently larger Trionyx among the Testudines in having a flexible ferox. margin. This margin varies in extent and thus in flexibility. In one species (Lissemys punctata) it makes up less than 10 percent of the spiniferus, T. steindachneri, T. sinensis, and total carapace length and contains bony ele- T. subplanus. All of the carapacial discs of T. ments which are most likely homologous to subplanus measured during the course of this the peripherals of other turtles (fig. 4A; see study are under 180 mm, but one unusually discussion of character 5 under section on large skull, BMNH 81.10.10.1 (figured as T. shell periphery). In other forms the carti- cartilagineus in Dalrymple, 1977), could have laginous margin makes up almost one-half of come from a specimen with a disc as large as the carapace length (fig. 4B) and the bony disc 250 mm. Awaiting complete analysis of the is thus quite reduced. relationship ofhead to shell size in this mega- There can be little doubt that reduction of cephalic form, T. subplanus is tentatively in- the bony disc relative to the total carapace is cluded among the smaller species. This list a derived condition, as it occurs only within of diminutive forms agrees in part with a list this family. However, variation in this con- assembled by De Broin (1977) based on skull dition among trionychid species shows no size. Her inclusion of T. leithii and T. ferox natural breaks and I have not been able to as small forms was clearly an artifact of small convert this continuous variable into a dis- sample size (see table 2). crete one. It should be pointed out, however, 1 987 MEYLAN: TRIONYCHIDAE 1 5

TABLE 3 Modal Character States for Shell Characters of the Recent Trionychidae Used in Analysis of Intrafamilial Relationshipsa Characters Species 1 2 3 4 5 7 8 9 10 12 13 14 15 16 17 18 19 20 21 23 24 25 29 aubryi 2 1 2 1 4 1 1 1 2 2 2 2 1 2 1 1 2 1 1 1 1 2 1 bibroni 3 2 2 2 4 1 1 3 1 1 1 2 1 1 3 2 1 1 2 2 1 1 1 cartilagineus 3 2 2 2 4 1 1 2 1 1 1 1 1 1 2 2 1 3 2 2 1 1 1 elegans 2 2 2 1 4 1 1 4 2 1 2 2 1 2 1 1 1 1 2 2 1 1 1 euphraticus 3 2 2 2 4 1 2 4 1 1 1 3 1 2 3 2 1 1 2 2 1 1 1 ferox 3 2 2 2 4 1 2 3 1 1 1 3 3 2 4 2 1 1 2 2 1 1 2 formosus 2 2 2 2 4 1 1 3 1 1 1 1 1 1 2 1 1 1 2 2 1 1 1 frenatum 2 1 1 1 4 1 1 1 2 1 2 2 1 2 2 1 2 1 1 1 1 2 1 gangeticus 3 2 2 1 4 1 1 2 1 1 1 2 2 2 3 1 1 2 2 2 1 1 1 hurum 3 2 2 1 4 1 1 2 1 1 1 1 2 2 3 1 1 2 2 2 1 1 1 indica 3 2 3 2 4 1 1 3 1 1 1 1 1 1 3 1 1 1 2 2 1 1 2 leithii 3 2 2 1 4 1 1 2 1 1 1 2 1 1 3 1 1 2 2 2 1 1 1 muticus 4 2 2 2 4 1 2 1 1 1 1 2 3 2 4 3 1 1 2 2 2 1 2 nigricans 3 2 2 1 4 1 1 2 1 1 1 1 1 2 3 - 1 2 2 2 1 1 1 punctata 2 1 1 1 3 2 1 1 2 2 2 4 1 2 2 1 2 1 1 1 1 2 1 senegalensis 3 2 2 1 4 2 1 0 2 1 2 5 - 4 - 1 1 1 1 1 1 1 1 sinensis 4 2 2 2 4 1 1 1 1 1 1 2 3 2 4 2 1 3 2 2 2 1 1 spiniferus 3 2 2 2 4 1 2 1 1 1 1 3 3 2 4 3 1 1 2 2 2 1 2 steindachneri 2 2 2 2 4 1 1 3 1 1 1 2 1 2 2 1 1 3 2 2 2 1 1 subplanus 4 2 2 2 4 1 1 3 1 1 1 1 2 0 2 3 1 3 2 2 2 1 1 swinhoei - - - 2 4 1 2 4 1 1 1 - - - - - 1 1 2 2 1 1 1 triunguis 3 2 2 2 4 1 1 3 1 1 1 3 1 2 3 2 1 1 2 2 1 1 1 a For descriptions of the characters and character states see table 1.

that cyclanorbines consistently have rela- of a long neck into a small space. In order to tively larger discs than trionychines and in accommodate such modification ofthis joint, this respect they represent the more primitive the entire anterior portion of the trionychid condition. carapace must have been extensively remod- Elsewhere (Meylan, 1985) I have suggested eled. In most cryptodires, the first thoracic that the shell outline ofCyclodermafrenatum vertebra is directly ventral to the first neural is unique in having a sharply tapering rear bone of the and is half carapace (fig. 6A) firmly of the carapace with straight-to-concave sutured to it. It is loosely jointed to the car- posterolateral edges (compare fig. 4A to figs. apace and usually more anteriorly located in 4B, SA, and SB). After examination of nu- trionychids (fig. 6B-D). In Lissemys and Cy- merous carapaces of Cycloderma aubryi and cloderma, the first thoracic vertebra lies di- Lissemys punctata, it is apparent that these rectly below the "preneural" to which it is species share the unique carapacial outline weakly sutured, suggesting that the "pre- noted above. Other trionychids, like most neural" is a first neural other actually (see also Baur, testudines, have round-to-oval shells 1893; Hay, 1908; Carpenter, 198 1). The nu- that are convex posteriolaterally (character chals of and 25, table Lissemys Cycloderma are also 3). the longest (relative to their width) among the trionychids (compare fig. 4A to figs. 4B, NUCHAL REGION SA, and SB). Separate anterior and posterior costiform processes can be recognized (fig. Dalrymple (1979) provides an excellent 6B). Grooves for passage of the postzyg- discussion of the role of the cervicodorsal apophyses of the eighth cervical vertebra are joint in trionychids in allowing the retraction present on either side of the midline at the 16 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 186

Fig. 4. Dorsal views of the carapace of two trionychid turtles. A. Lissemys punctata (UF 56017); B. Trionyx subplanus (MNHNP unnumbered, holotype, with details from BMNH 5 3.5.38). base of the posterior costiform process. This other than the Indian forms: T. hurum, T. combination of features places a well-fixed leithii, T. nigricans, and T. gangeticus. Up to first thoracic vertebra well back from the edge about 10 percent of certain Trionyx species of the carapace (fig. 6B). Among trionychids (T. ferox, T. formosus, T. triunguis) show sep- the condition in Lissemys and Cycloderma arate first and second neurals. most closely approaches that seen in other The extreme of development in this suite cryptodires. Further derived conditions in- of characters is found in Chitra (fig. 6D). In clude less contact between the first thoracic C. indica, prezygapophyses of the first body vertebra and the first neural and more pos- vertebra are immediately adjacent to the anterior placement of the nuchal such that it terior rim of the carapace, and the nuchal is lies above the first thoracic vertebra. reduced to a narrow sliver of bone. Very nar- An advanced condition of the nuchal re- row costiform processes occur on the anterior gion appears in Cyclanorbis senegalensis, in margin, and depressions which allow passage which the length of the nuchal bone is re- ofthe postzygapophyses ofthe eighth cervical duced, bringing the first thoracic vertebra are present just inside the rim ofthe carapace. closer to the anterior edge of the carapace. In Chitra there is also a new pair of processes The anterior and posterior costiform pro- at the posterior edge of the nuchal. They can cesses of the nuchal are not clearly separate be distinguished from the posterior pair in (as in figs. 6C, D), but the first neural (pre- Cycloderma and Lissemys by their position neural) is still distinct from the second (as in well posterior to depressions for passage of figs. 4A and 5B). A similar condition is found the postzygapophyses of the eighth cervical. in Cyclanorbis elegans and in Trionyx gan- Variation in the nuchal region has been geticus, T. leithii, T. nigricans, and T. hurum. analyzed through the use of four characters Fusion of the first and second neurals oc- (tables 1, 3). The primitive condition for nu- curs only when the first thoracic vertebra is chal shape (character 1) is that most similar free of overlying neurals due to reduction of to those of other turtles, that is, length equal the neural arch of the vertebra. It is present to width or nearly so. Costiform processes in all Chitra, Pelochelys, and Recent Trionyx (character 2) are not present in adult Caret- 1987 MEYLAN: TRIONYCHIDAE 17

Fig. 5. Dorsal views of the carapace of two trionychid turtles. A. Trionyxferox (AMNH 129737); B. Trionyx hurum (BMNH 86.8.22.2). tochelys, but in some juveniles of the related shell comes to lie closer to the first thoracic genus Anosteira, there are two pairs (Bram- vertebra. Close proximity ofthe anteriormost ble, personal commun.). In other triony- thoracic vertebra to the margin of the cara- choids (Kinostemidae and Dermatemydi- pace is considered derived (character 3, table dae) there is one pair in adults. But in newly 3). hatched Dermatemys (BMNH 1984.1291) The trionychid "preneural" is here consid- there are, in fact, two pairs. A cleared and ered to be the first neural (see also Hasan, stained hatchling Sternotherus minor and a 1941). As suggested by Webb (1962) and skeletonized Kinosternonflavescens in the UF Gaffney (1979c), fusion of the first neural to collection also have indications of paired the second neural must be a derived character processes anterior to a well-defined pair of state (character 4). No nontrionychid mem- costiform processes. Thus it seems likely that ber of the Trionychoidea always has two two pairs are present early in the ontogeny neurals between the first pleurals, but there of all trionychoids. In the Dermatemydidae are two in some Carettochelys (BMNH and Kinostemidae the anterior of the two 1903.4.10.1). Furthermore, there are two pairs disappears with age while in the Tri- thoracic vertebrae between the first pleurals onychidae the two pairs occur separately in of all trionychids. In T. ferox two neurals some forms (Lissemys punctata and both form (one on each of the first two thoracic species of Cycloderma) and appear to be vertebrae) and then fuse into a single element united in all others. Because this condition is (Carpenter, 1981; present study). probably present early in the ontogeny of all The carapace of adult turtles is ordinarily trionychoids, the possession of two pairs of a solid bony structure without openings or costiform processes is considered primitive fontanelles. Peripheral fontanelles are not un- for trionychids. common; they occur in juveniles of all cryp- Most cryptodires have the first thoracic todires and are retained in some adult che- vertebra at the posterior edge of the nuchal. lydrids, cheloniids, and trionychids. In As a result of apparent foreshortening of the trionychids, peripheral fontanelles are diffi- nuchal in trionychids, the anterior edge ofthe cult to visualize because the peripheral bones 18 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 186

A B

Fig. 6. Internal views of the carapace of four eucryptodiran turtles. A. Trachemys scripta (AMNH 111961); B. Lissemys punctata (UF 56017); C. Trionyxferox (AMNH 129737); D. Chitra indica (MCZ 29487). Surfaces for ilial articulation are stippled. are lacking. Fontanelles closer to the midline tanelles) in certain trionychids and at least ofthe carapace are much less common. They one testudinid, Homopus. occur above the ilia in very old individuals Suprascapular fontanelles are probably of some testudinoids (e.g., Terrapene, Cuora, present early in the development of all trion- Gopherus, Homopus) and some Kinosternon, ychids. They are closed at hatching in some and above the scapulae (=suprascapular fon- forms (Lissemys punctata) but remain open 1987 MEYLAN: TRIONYCHIDAE 19

TABLE 4 TABLE S Suprascapular Fontanelies (Character 18) in the Number of Neurals in Recent Trionychid Carapace of Recent Trionychidsa Turtlese

Species A B C Species N 7 8 9 10 aubryi none 65.0 365.0 aubryi 17 0.71 0.29 bibroni 71.0 200.0 415.0 bibroni 10 0.10 0.20 0.70 cartilagineus 174.0 172.0 316.0 cartilagineus 18 0.17 0.78 0.06 elegans none 182.0 475.0 elegans 14 0.21 0.43 0.36 euphraticus 273.0 217.0 273.0 euphraticus 6 1.00 ferox 237.0 120.5 315.0 ferox 31 0.06 0.88 0.06 formosus none 156.0 156.0 frenatum 5 0.20 0.20 0.60 frenatum none 180.0 535.0 gangeticus 7 0.71 0.29 gangeticus 106.0 205.0 460.0 hurum 5 0.20 0.80 hurum none 132.0 292.0 indica 13 1.00 indica none 180.0 550.0 leithii 3 0.33 0.67 leithii none 205.0 380.0 muticus 7 0.43 0.57 muticus 124.0 none 124.0 punctata 19 0.21 0.74 0.05 punctata none 60.0 277.5 senegalensis 17 0.18 0.06 senegalensis none 113.0 294.5 sinensis 25 0.40 0.60 sinensis 140.0 117.0 242.0 spiniferus 18 0.06 0.88 0.06 spiniferus steindachneri 3 0.33 0.67 males 89.5 85.0 89.5 subplanus 10 0.80 0.20 females 186.5 none 186.5 triunguis 14 0.92 0.08 steindachneri 170.0 none 170.0 a Values represent the frequency of occurrence for the 177.0 none 177.0 subplanus sample. A fused first and second neural is counted as triunguis 83.5 197.0 410.0 two elements. Seventy-six percent of Cyclanorbis sene- a Disc length (mm) for the largest specimens with fon- galensis have 6 or fewer neurals. Trionyxformosus, T. tanelles (A), smallest specimen without fontanelles (B), nigricans, and T. swinhoei are excluded due to insuffi- and largest specimen examined for fontanelles (C) are cient sample size. given for each species. All trionychids lack a suprapygal, and the throughout life in others (Trionyx subplanus, eighth pleurals meet at the midline (except T. spiniferus [except some old males], T. mu- in Trionyx subplanus). The most complete ticus, and T. steindachneri). In most triony- series ofnine neurals, with all or the majority chids suprascapular fontanelles close up at (numbers 2-7) hexagonal and uniformly fac- some point between hatching and the attain- ing posteriorly (see below), is likely to be the ment of adult size (table 4). However, insuf- most primitive condition among living trion- ficient data on the timing of closure in most ychids. species prevents the use ofthis character. Ear- Modification of the presumed primitive ly loss ofthe fontanelles is likely the primitive condition results from four apparently in- condition and lifelong retention derived. dependent changes: (1) the fusion of the first and second neural (treated above, character 4), (2) interruption of the neural series by THE NEURAL SERIES pleurals meeting at the midline (character 16), The above argument suggests that the (3) variation in the number of neurals ex- trionychid "preneural" of many authors is pressed on the dorsal surface of the carapace the first neural. Thus the most complete neu- (character 14, table 5), and (4) variation in ral series in trionychids includes nine ele- the location at which orientation of the neu- ments between the nuchal and eighth pleurals reverses (character 17, table 6). There are rals. The normal pattern in cryptodires is a also interspecific differences in the amount of continuous series of neurals from the nuchal variability in the point of neural reversal to the suprapygal, with uniform orientation. (character 15). That is to say, in some species 20 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 186

TABLE 6 Location of Reversal in Neural Orientation in Recent Trionychidsa 4/5 or Species N anterior 5 5/6 6 6/7 7 7/8 8 aubryi 17 0.12 0.06 bibroni 10 0.10 0.30 0.50 0.10 cartilagineus 18 0.28 0.17 0.44 0.06 0.11 elegans 14 0.43 euphraticus 6 0.17 0.33 0.33 0.17 ferox 31 0.16 0.13 0.19 0.32 0.19 frenatum 5 0.20 0.40 0.20 gangeticus 7 0.57 0.43 hurum 5 0.40 0.20 0.40 indica 13 0.08 0.92 leithii 3 0.33 0.33 0.33 muticus 7 0.14 0.14 0.57 0.14 punctata 19 0.32 0.11 sinensis 25 0.08 0.08 0.12 0.28 0.40 0.04 spiniferus 18 0.28 0.11 0.33 0.06 0.17 0.06 steindachneri 3 0.33 0.33 subplanus 8 0.25 0.63 0.13 triunguis 14 0.08 0.69 0.08 0.15 a Location of the most posterior reversal is given as a frequency of occurrence at or between neurals. Values which do not sum to 1.0 are due to individuals with no neural reversal (see table 7). Trionyxformosus, T. nigricans, and T. swinhoeiare excluded due to insufficient sample sizes; in Cyclanorbis senegalensis the neural series is too fragmented to allow the detection of reversals. the location of reversal is always at the same lated from the rest of the neural series in neural; in others, neural reversal occurs only occasional specimens of Lissemys punctata at either of two adjacent neurals; and in still (2 of 19), Trionyx ferox (5 of 31), T. gan- others, it may occur anywhere along the neu- geticus (1 of 7), and T. hurum (1 of 5). More ral series. frequent neural isolation occurs only in the Interruption of the neural series by pleurals two species of Cyclanorbis. Siebenrock (1902) meeting at the midline is not common among discussed the marked variability ofthe neural cryptodires. Most species have a neural series series in these two species in his paper which which is uninterrupted from the nuchal to established the existence of the two forms on the suprapygals. In dermatemydids and kin- osteological grounds. Both Cyclanorbis osternids, posterior pleurals may meet on the species can have long continuous rows of midline but in this case the posteriormost neurals or many isolated neurals. Although neurals usually do not appear and so they C. senegalensis tends to have more isolated cannot be isolated from the anterior portion neurals than C. elegans, the most reliable di- of the series. In Carettochelys pleurals often agnostic features of these two species are meet along the midline, isolating sections of found in the plastron. C. senegalensis is the neural series. The neurals ofCarettochelys unique among living trionychids in possess- are extremely narrow and thus appear to be ing gular callosities. C. elegans is unique less generalized than those of trionychids. among cyclanorbines in having callosities of Relying on global parsimony in establishing the fused hyo-hypoplastra that are flat or con- polarity in this case, I must consider the ab- cave along their anterior edge. sence of pleural interruption of the neural The number of neurals appearing on the series primitive for the Trionychidae. surface of the carapace in trionychids varies Actually, interruption of the neural series from 3 to 10. The occurrence ofa tenth neural is rare in trionychids. The last neural is iso- is very rare (3 of 242 specimens, two Trionyx 1 987 MEYLAN: TRIONYCHIDAE 21 subplanus and one T. cartilagineus) and seems of the next posterior neural (fig. SB, neural to be anomalous. Thus, nine neurals make 7). The second and less common reversal oc- up the most complete series, and the posses- curs via two successive asymmetrical pen- sion of nine neurals is considered to be the tagonal neurals (fig. 4B, neurals 7 and 8). The fundamental condition for trionychids. This anterior of the pair contacts an anterior short is not supported by evidence from the outside of one of the next posterior pair of pleu- groups. All other members of this superfam- rals, while the posterior neural contacts a short ily have lost varying portions of the posterior posterior side of the preceding pleural on the neural series. This makes determining a opposite side. primitive number based on the trionychoids In the presumed primitive neural arrange- alone quite difficult. ment, reversal of neural orientation, if it oc- Looking outside of the Trionychoidea, one curs at all, is posteriorly located. But in many finds nine neurals commonly in the Chelyd- forms, reversal occurs anteriorly and this is ridae, where they are packed closely together considered to be derived. Such reversal usu- posteriorly. In the Cheloniidae, Chelonia my- ally accompanies other changes from the das and Eretmochelys imbricata frequently primitive neural configuration. Reversals can have two neurals between the first pair of occur from neural one through eight and mul- pleurals, as is proposed to be primitive for tiple reversals are common in some species trionychids (see, for example, fig. 8 in De- (treated separately as character 16; tables 6, raniyagala, 1939). Other sea turtles have 7). Where multiple reversals occur the loca- higher numbers of neurals but this is due to tion of the most posterior one is thought to division of neural elements (Zangerl and indicate the degree of anterior migration of Tumbull, 1955), and nine neurals may ac- neural reversal. Data on location of neural tually be the primitive number for these reversal are treated as five states of character species as well. 17 (tables 1, 3), with the most anterior being Variation in the number of neurals among most derived. Data on the amount of intra- living trionychids is given in table 5. The specific variability in the location of the last number of neurals (character 14, tables 1, 3) neural reversal are treated via three states of is treated as five character states, with nine character 15 (tables 1, 3), with the most vari- neurals considered most primitive and seven able being considered most derived. or fewer neurals most derived. Nearly all neurals of trionychids are six- sided (see figs. 4, 5). Anterior and posterior SHELL PERIPHERY ends of each neural contact adjacent neurals, With the exception of the Trionychidae, the four lateral sides contact four adjacent the margin of all testudine carapaces is solid. pleurals, but the anterior and posterior pairs This is due to the presence ofperipheral bones of pleural contacts are of unequal length, one that form a complete ring around the cara- usually being significantly longer than the pace. In nearly all turtles this ring is com- other. In the anterior part of the neural series posed of22 peripheral elements, a nuchal and the shorter pleural contacts face posteriorly, a pygal. Only in the Trionychoidea is there but in the posterior part of the series (in most reduction and complete loss of these ele- species) the shorter contacts face anteriorly. ments. In all kinosternids and Carettochelys Thus, there is usually a reversal in orientation there is one fewer peripheral on each side of these anterioposteriorly asymmetrical ele- (total of 20). Peripherals 2 through 10 in Ca- ments in every neural series. rettochelys are not sutured to the pleurals, Reversal of orientation occurs in two ways. which is also true for the only trionychid More commonly it occurs via a four-sided which retains bones in the periphery, Liss- neural (=a "diaphragmatic" neural of Hum- emys punctata (character 6, table 3). mel, 1929). The pair of pleurals adjacent to The homologies of the bones in the pe- this four-sided neural contacts the two pos- riphery of the shell of Lissemys have been terior-facing short sides of the next anterior questioned by many authors. Boulenger neural, and the two anterior-facing short sides (1889), Loveridge and Williams (1957), Zan- 22 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 186

TABLE 7 TABLE 8 Number of Reversals of Orientation in the Modal Character States for Shell Characters of Neural Series of Recent Trionychidsa the Recent Trionychidae Used in Analysis of Interfamilial Relationshipsa Species N 0 1 2 3 aubryi 17 0.82 0.18 Character states bibroni 10 1.00 Taxa 5 6 22 26 27 28 30 cartilagineus 18 1.00 elegans 14 0.57 0.43 Trionychidae 3/4 2 2 3 2 2 2 euphraticus 6 1.00 Carettochelys 2 2 1 3 2 2 2 ferox 31 0.66 0.31 0.03 Claudius 2 1 1 3 2 1 1 frenatum 5 0.20 0.80 Staurotypus 2 1 1 3 1 1 1 gangeticus 7 1.00 Kinosterninae 2 1 - 3 1 1 1 hurum 5 1.00 Dermatemys 1 1 1 2 1 1 1 indica 13 1.00 Chelydridae 1 1 1 3 2 1 1 leithii 3 1.00 Platysternon 1 1 1 3 2 1 1 muticus 7 0.86 0.14 Cheloniidae 1 2 1 3 2 1 1 punctata 19 0.58 0.42 Emydidae 1 1 1 1 lb 1 1 sinensis Testudinidae 1 1 1 1 1 1 1 25 0.80 0.16 0.04 lb spiniferus 18 0.44 0.28 0.28 Pleurodira 1 1 1 1 2 1 steindachneri 3 0.33 0.67 a For descriptions of characters and character states subplanus 8 1.00 see table 1. triunguis 14 1.00 b Except in kinetic forms. a Number of reversals is given as a frequency. Trionyx formosus, T. nigricans, and T. swinhoei are excluded due usually about 18 in number (Deraniyagala, to insufficient sample sizes; in Cyclanorbis senegalensis the neural series is too fragmented to allow the detection 1939). Peripherals are absent in all other of reversals. trionychids. The reduction and loss of bones in the periphery is clearly derived (character 5, tables 1, 3, 8). gerl (1969), and others have considered these Although the rib heads ofeach pleural bone bones to be neomorphic structures. Walther normally reach the centrum of the corre- (1922), Webb (1982), and Meylan (1985) have sponding thoracic vertebra, the contact is not treated the peripherals of Lissemys as homo- always a strong one. Only in trionychids and logs of the peripherals of other turtles. Al- Carettochelys among the Cryptodira have I though these elements are found in the car- found strong, interlocking sutures (character apace only posterior to the bridge and they 29, tables 1, 8). Richmond (1964) has sug- lack one-to-one correspondence with the gested that the peripheral bones of most tur- pleurals, there is other evidence which sug- tles form a locking ring between the arched gests that they are degenerated peripherals carapace and the plastron, which acts as a and not neomorphs. In cross section the pe- tension member. This keeps the shell from ripheral ossifications of Lissemys are like expanding laterally when a dorsoventral force those of other turtles in that they consist of is applied. It is possible that these strength- two laminar layers of bone which converge ened contacts between the rib-heads and ver- distally (fig. 7). Between these two layers is tebral centra may be an alternative means of cancellous bone. Lissemys peripherals differ countering such forces. Thus the carapace of from those of other turtles principally in the Carettochelys may be "preadapted" for the absence of the proximal portion. Unless some loss of peripherals. developmental constraint that results in the Both Lissemys punctata and Cyclanorbis formation of V-shaped elements in the pe- senegalensis possess a prenuchal that is an riphery of all turtle shells can be identified, isolated element that lies above the neck, just it may be best to consider these details of anterior to the nuchal (character 6, tables 1, morphology as evidence of homology. 3). The prenuchal is a neomorph not found Peripherals are found in the carapace of in any other cryptodire, and its appearance Lissemys only posterior to the bridge and are is a derived condition. 1 987 MEYLAN: TRIONYCHIDAE 23

Fig. 7. Cross sections of a single peripheral of two cryptodires. Top, Lissemys punctata (UF 56017); bottom, Chrysemys picta (UF 40615). norbis elegans, articulate with the eighth POSTERIOR END OF CARAPACE pleurals, as they do in other cryptodires. In all trionychines and in C. elegans the ilia ar- In nearly all turtles, the eighth and last pair ticulate with the tough connective tissue just of pleurals forms as significant a portion of posterior to the end ofthe shell. The presence the carapace as those which precede it. Al- ofdistinct areas ofcontact (either depressions though the eighth pleurals of trionychids de- or tubercles) for the ilia on the eighth pleurals velop allometrically, being relatively larger (fig. 6B) is considered primitive, their ab- in adult turtles than in juveniles, it is still sence derived (character 21, table 3). possible to detect a difference in their size among species (compare figs. 4 and 5). In PLASTRON some forms they are large, in others somewhat reduced, and in yet others they are ab- The plastron of most cryptodires includes sent. The presence of large eighth pleurals nine elements (one pair each of epi-, hyo-, provides a complete complement of pleural hypo-, and xiphiplastra and a single ento- bones. The reduction of this complete com- plastron). These nine elements are usually well plement is considered to be derived. Large sutured to one another and form a solid bony eighth pleurals are present in all cyclanor- structure. The same nine elements are present bines as well as all Old World trionychines, in all trionychids (Bramble and Carr, MS), but except Trionyx euphraticus. There is a trend they are relatively incomplete; they are often toward the loss of the eighth pleurals in New not sutured to one another and do not result World forms (character 8, tables 1, 3). in a single solid structure. Where plastral su- The ilia of cyclanorbines, except Cycla- tures are present in trionychids they occur 24 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 186

A B

C D

Fig. 8. Ventral views of the plastra of four trionychid turtles, with right xiphiplastra stippled. A. Cycloderma aubryi (MRAC 19212); B. Lissemys punctata (UF 56017); C. Trionyx sinensis (modified from Heude, 1880); D. T. ferox (AMNH 129737). between the superficial dermal callosities with onyx, but only in Lissemys punctata and minor contributions from underlying ele- Cycloderma aubryi does a sutured contact oc- ments. The presence of sutures, and thus of cur. This suture fuses in very old individuals the callosities that allow them to occur, is of these two species. Sutures are absent be- interpreted as a primitive condition. tween epi- and entoplastron, entoplastron and A suture is found between the hyo- and hyoplastra, hypo- and xiphiplastra, and along hypoplastra of all trionychids, and, in many, the midline (except for the xiphiplastra ofthe fusion occurs along this suture. The xiphi- two species noted above) in all Recent trion- plastral callosities make contact at the mid- ychids. line in large Lissemys, Cycloderma, and Tri- The number of plastral callosities in all 1 987 MEYLAN: TRIONYCHIDAE 25 trionychids increases with age but is stable in Thus the presence of the hypoplastron lateral large adults (character 9). Callosities are pres- to the xiphiplastron at their junction is con- ent on all nine plastral elements in certain sidered to be a derived condition unique to species and this is proposed as the primitive cyclanorbine trionychids (character 13, table condition (fig. 8A, B). The callosities cover- 3). ing the hyo- and hypoplastron on each side Relative to the epiplastra of other Testu- are here considered to be a single structure dines those of trionychids are quite reduced making seven the primitive number. Seven in basic structure. The deep element, which callosities are found in Lissemys, Cycloder- may or may not be covered by a callosity, is ma, and some Trionyx. Derived conditions I- or J-shaped. The J-shaped elements have include both an increase and a decrease in a long ramus that is oblique to the midline the number of callosities (character 9, tables and has a long contact with the entoplastron 1, 3). Only Cyclanorbis senegalensis has in- (fig. 8C, D). They also have an anterior pro- creased the number of callosities by the ad- jection of variable length that roughly par- dition of a gular pair. The cyclanorbine Cyc- allels the midline. I-shaped elements consist lanorbis elegans parallels the trend in the of only the anterior portion and have mini- Trionychinae in having marked reduction in mal contact to the entoplastron (fig. 8B). the number of callosities to two. J-shaped epiplastra are found in all triony- Although the fusion of two plastral ele- chids except Lissemys punctata, Cycloderma ments is certainly derived, it can occur only aubryi, and Cyclodermafrenatum, which have when the primitive condition, a suture be- the alternate I-shape. tween two elements, is present. Thus the Long medial contact between the epiplas- xiphiplastral suture in Lissemys punctata and tra and the entoplastron occurs in all non- Cycloderma aubryi suggests that they are trionychid turtles in which these elements are primitive. However, xiphiplastral fusion is present. The posterior contact ofthe J-shaped unique to these forms among trionychids and epiplastra to the entoplastron maintains this is considered a shared derived state (char- contact and thus the J-shape is considered acter 12, table 3). primitive, the I-shape derived (character 19, Hyo-hypoplastral sutures occur at some table 3). stage in the ontogeny of all extant triony- The anterior extension of J-shaped epi- chids. Recent cyclanorbines share the com- plastra varies in length among the species in mon character state of hyo-hypoplastral fu- which it is found (compare fig. 8C and 8D). sion at a very small size (as small as 62 mm The extension beyond the entoplastron var- disc length). Fusion of the hypoplastra to the ies from 0.16 to 0.48 times the width of the hypoplastra occurs in all adult Trionyxferox hypoplastron of the right side (table 9). It is (fig. 8D) and in adults of some populations difficult to be certain which length of the ex- of T. triunguis. Hyo-hypoplastral fusion is tension is primitive for trionychids but it considered to be derived and to occur inde- seems clear that the marked extension of Tri- pendently in cyclanorbines and trionychines onyx cartilagineus, T. subplanus, T. sinensis, (characters 10 and 1 1, tables 1, 3). and T. steindachneri is derived. As suggested The xiphi-hypoplastral union in triony- by De Broin (1977), the species of the Indian chids is of two types. In all trionychines the subcontinent have epiplastra of intermediate two anterior xiphiplastral processes lie on length relative to the most elongate forms and either side of the most lateral of the three other trionychids. Variation in this feature is posterior processes of the hypoplastron (fig. treated as three states of character 20 with 8C, D). In cyclanorbines the two anterior pro- the longest extension considered to be most cesses of the xiphiplastron lie on either side derived (character 20, table 3). of the middle of the three posterior processes The boomerang shape of the entoplastron of the hypoplastron (fig. 8A, B). The trion- of trionychids is unique among turtles (char- ychine condition occurs in cheloniids, Ca- acter 22, table 8). Zangerl (1939) has implied rettochelys, and among kinostemids (Kino- that a T-shaped entoplastron is primitive for sternon, Sternotherus, and Staurotypus), reptiles. The entoplastron in trionychids ap- suggesting that it is the primitive condition. parently arises from a proliferation and bend- 26 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 186

TABLE 9 width (fig. 8A, B), and those species with a Extension of the Right Epiplastron Beyond the bridge less than one-half hypoplastron width Entoplastron, Relative to Total Hypoplastron (fig. 8C, D). The former group includes all Width of the Right Side (Character 20)a cyclanorbines except Cyclanorbis elegans; the Species N x 1 S.D. latter includes all trionychines plus Cycla- norbis elegans. bibroni 3 0.165 0.042 cartilagineus 4 0.482 0.022 Long plastral bridges occur in Dermatemys elegans 2 0.356 0.019 and Carettochelys but not in kinosternids. euphraticus 2 0.263 0.025 They are also long in testudinoids, with the ferox 13 0.228 0.019 exception of the most kinetic forms. Thus a formosus 1 0.287 - long bridge is considered to be primitive, a gangeticus 2 0.314 0.038 short bridge derived (character 23, tables 1, hurum 2 0.358 0.010 3, 8). indica 5 0.230 0.011 In addition to being short, the bridges of leithii 3 0.312 0.021 trionychid turtles lack ascending buttresses muticus 3 0.183 0.017 and sutured contacts to the elements of the senegalensis 3 0.280 0.015 sinensis 13 0.423 0.036 carapace. Ascending processes cross the pe- spiniferus 10 0.248 0.024 ripherals to contact the pleurals in both the steindachneri 2 0.418 0.014 axillary and inguinal regions in pleurodires subplanus 5 0.479 0.039 and testudinoids except for those taxa with swinhoei 1 0.221 well-developed plastral kinesis. In Derma- triunguis 3 0.228 0.023 temys only the axillary buttress reaches the pleurals. In all other living families the but- a Sample size, average, and one standard deviation are given for each species. Species with I-shaped epiplastra tresses are quite reduced and do not cross the and T. nigricans are not included. peripherals (character 26, tables 1, 8). The distribution of the states of this character can be explained about as parsimoniously by loss ing of the transverse portion of the T, com- or by gain of buttress to pleural contact if bined with suppression ofdevelopment ofthe only Recent forms are examined. However, longitudinal portion. The amount of bending buttress-to-pleural contact occurs in such ex- of the transverse bar varies among triony- tinct cryptodiran families as the Baenidae, chids and results in an angle of 62 to 1220 Plesiochelyidae, and Meiolaniidae, suggest- between the two posteriolaterally directed ing that the presence of this contact is in fact rami. Variation within each species spans the primitive condition. about 15°. Variation among species is quite In a few taxa that lack large plastral but- continuous, with no natural breaks. Estab- tresses, the plastron is not strongly sutured lishing a polarity for this character has not to the carapace at the bridge. This occurs in been possible because no other members of chelydrids, cheloniids, Claudius, Carettoche- the Trionychoidea have similar entoplastron lys, and trionychids and is considered a de- morphology. Difficulty in establishing polar- rived condition (character 27, tables 1, 8). ity, combined with problems of variability, has made it impossible to include the angle of the entoplastron as a character in the in- VARIATION IN SKULL trafamilial analyses. MORPHOLOGY Plastral reduction in trionychids includes The value of the trionychid skull in sys- a marked reduction in the length ofthe bridge. tematics has been recognized by numerous Bridge length was compared to hypoplastron authors (Gray, 1864, 1869, 1873a, 1873b; width as an index of this reduction. Bridge Boulenger, 1889; Hummel, 1929; Loveridge length varies from more than three-quarters and Williams, 1957; De Broin, 1977). As of hypoplastron width (Cycloderma aubryi) pointed out by Loveridge and Williams (1957) to about one-eighth hypoplastron width (Tri- there has been too much emphasis on the size onyx subplanus). But variation falls into two and form of the jaws and too little on details discrete groups: those species in which the of morphology and contacts of skull ele- bridge is well over one-half hypoplastron ments. Numerous authors have expressed 1987 MEYLAN: TRIONYCHIDAE 27 concern about the validity of characters of Among trionychoids this is true only for der- the size and shape of the jaws (Boulenger, matemydids and kinosternids. In Carettoche- 1889; Villiers, 1958; Barghusen and Parsons, lys, as well as all trionychids, these normally 1966; Eiselt, 1976; De Broin, 1977). But only paired elements are fused to one another Dalrymple's (1977) account of variation in (character 44, tables 10, 12; figs. 9A, C, D, the skull of Trionyxferox treats the correla- lOA, B). In trionychids this fused premaxil- tion of skull size and shape to environmental lary differs further from those of the out- factors in a detailed and systematic fashion. groups in being excluded from the apertura Dalrymple has found that the most variable narium externum by the maxillae which meet features of size and shape of the skull of T. dorsal to it (character 45, table 12; figs. 9A, ferox are those which relate to feeding. Those C, lOA, B). structures which provide sites of origin or In three trionychids the premaxillary is passage for jaw musculature increase allo- either often absent (Chitra indica, 4 of 10), metrically with age, and the amount of rel- or nearly always absent (Cycloderma frena- ative increase is highly variable. Further- tum, 4 of 5; Pelochelys bibroni, 6 of 7) (char- more, the development of features related to acter 65, table 1 1). The absence of this ele- feeding can occur independently of one ment is clearly derived. another. This high degree of variability in Because nasals are absent in all triony- characters of the feeding apparatus indicates chids, as they are in all living cryptodires that they are not useful systematic features, (Gaffney, 1979b), the prefrontals are the an- as had been suspected. teriormost paired elements on the dorsal sur- In this study quantitative characters of the face of the skull. Thus, the prefrontals form jaws and associated structures (palatal groove, the dorsal border of the apertura narium ex- supraoccipital spine) are avoided. Treatment ternum. Laterally these elements contact the of the skull concentrates on contacts between maxillae and border the anterior portion of elements and on contacts between elements each orbit between the maxilla and frontal. and features ofexternal morphology. Because In most cryptodires the descending processes complete interspecific comparison is the goal of the prefrontals contact the vomer and pal- of this study, data from sectioned skulls (8 atines. There is significant variation among of 22 trionychid species available) will not trionychids in these contacts. There is also be treated. This is the first study of trionychid useful variation in the degree ofemargination systematics for which at least one skull of of the prefrontals at the dorsal edge of the every currently recognized Recent species was apertura narium externum and in the degree available. of separation of the maxillae and frontals The skull characters and character states along the anterior margin of the orbit. which are treated in this section are sum- Through reduction of the prefrontals, marized in table 10. The details of distribu- vomer, and palatines, contact between the tion of the states of characters important for prefrontals and palatal elements in triony- resolving relationships within the Tri- chids is greatly reduced, or lost. The prefron- onychidae are given in table 11. The states tal-palatine contact found in most crypto- for characters important for resolving interfa- dires is lost in all trionychids (Gaffitey, 1979b) milial relationships are given in table 12. and this loss can be considered a shared de- Character states which are autapomorphic for rived character for the family (character 38, a living trionychid species are listed in table table 12). Contact between the vomer and 13. Discussion ofthese characters is arranged prefrontals is the common condition among by region of the skull beginning anteriorly trionychids, as it is for all testudines (fig. 1 OA). and proceeding posteriorly, with the dorsal It is absent only in Cycloderma aubryi, Cy- surface treated first. clodermafrenatum, Cyclanorbis senegalensis and Chitra indica (fig. lOB), and is clearly a NASAL REGION derived condition (character 36, table 11). With the exception of two very primitive The premaxillae of cryptodires are usually forms, Proganochelys and Kallokibotion, tes- paired elements that make up the ventral edge tudines have an unpaired apertura narium of the apertura narium externum (fig. 9B). externum with a nearly straight to somewhat 28 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 186

TABLE 10 TABLE 10-(Continued) Systematic Characters and Character States of Characters Character states the Trionychid Skull 52. processus pterygoideus 1. yes Characters Character states externus projects from 2. no 31. quadratojugal contacts 1. yes pterygoid maxillary 2. occasionally 53. size of foramen palati- 1. large 3. no num posterius 2. small 32. jugal contacts squamosal 1. no 3. small and divided 2. in one-half of 4. many small open- sample ings 33. quadratojugal contacts 1. yes 54. foramen palatinum pos- 1. palatine and pter- postorbital 2. no terius forms in ygoid and/or 34. jugal contacts parietal on 1. no maxilla skull surface 2. in one-half of 2. palatine only sample 55. basis tuberculi basalis 1. yes 3. yes present 2. no 35. jugal contacts parietal 1. no 56. foramen posterius canalis 1. no within fossa temporalis 2. yes carotici interni complete- 2. yes 36. vomer contacts prefrontal 1. yes ly within pterygoid 2. no 57. canalis carotici interni 1. no 37. incisura columella auris 1. no straight and wide 2. yes closed 2. yes 58. foramen jugulare poster- 1. no 38. palatines contact prefron- 1. yes ius excluded from fenes- 2. yes tals lateral to vomer 2. no tra postotica by pterygoid 39. cheek emargination ex- 1. yes arching to contact opis- tends above lower edge 2. no thotic of orbit 59. foramen jugulare poster- 1. no 40. anterior limit of cheek 1. maxilla ius excluded from fenes- 2. yes emargination formed by 2. jugal tra postotica by descend- 41. dorsal edge of apertura 1. no ing process of opisthotic narium externum lateral- 2. weakly which reaches pterygoid ly emarginate 3. strongly 60. foramen posterius canalis 1. above 42. dorsal edge of apertura 1. no carotici interni relative to 2. in it narium externum medial- 2. yes lateral crest of basioccipi- 3. below ly emarginate tal tubercle 43. palatine forms a signifi- 1. no 61. groove for some portion 1. yes cant part of the lateral 2. yes of stapedial artery visible 2. no wall of the braincase on prootic or descending 44. premaxillae fused into 1. no process of parietal single element 2. yes 62. maxilla contacts frontal 1. no 45. premaxillae enter aper- 1. yes in front of orbit 2. yes tura narium extemum 2. no 63. exoccipital contacts pter- 1. no 46. basisphenoid contacts 1. no ygoid 2. yes palatines 2. yes 64. basisphenoid shape 1. not medially con- 47. foramen intermaxillaris 1. absent stricted 2. present 2. occasionally me- 48. vomer divides maxillae 1. yes dially constricted 2. no 3. medially con- 49. vomer reaches intermax- 1. yes stricted illary foramen 2. no 65. premaxilla absent 1. no 50. vomer contacts pterygoid 1. yes 2. occasionally 2. occasionally 3. usually 3. no 66. vomer lost 1. no 51. vomer contacts basisphe- 1. no 2. yes noid 2. occasionally 67. jugal contacts orbit 1. yes 2. no 1 987 MEYLAN: TRIONYCHIDAE 29

TABLE 10-(Continued) or quite deep (fig. 9B) (character 41, table 1 1). Characters Character states Only in Cyclanorbis elegans does emargination occur medially (character 42, table 13). 68. epipterygoid, if present, 1. yes The condition in C. elegans is considered to contacts the palatine 2. in ca. 50% occur independently from that in other emar- 3. no ginate forms. Weak lateral emargination is 69. contact between ptery- 1. yes considered to be intermediate between the goid and foramen nervi 2. no trigemini occurs when strongly emarginate and nonemarginate con- epipterygoid is present ditions. 70. when epipterygoid is 0. between epiptery- It is the prefrontal that normally separates present pterygoid con- goid and quadrate the maxilla from the frontal at the anterior tacts foramen nervi tri- or not at all edge of the orbit in turtles. In a single trion- gemini 1. between prootic ychid, Trionyx subplanus, the maxillae con- and epipterygoid tact the frontals lateral to the prefrontals in or not at all about one-half of the specimens examined. 2. between epiptery- In the others, these elements are quite close goid and parietal and their proximity can be considered a or not at all 71. epipterygoid contacts 1. no unique feature of this species (character 62, prootic anterior to fora- 2. in ca. 50% table 13). men nervi trigemini 3. yes 72. epipterygoid contacts 1. no ORBITAL REGION prootic posterior to fora- 2. yes men nervi trigemini A frequently used character in trionychid 73. epipterygoid fuses to 1. in subadults systematics is the relationship between the pterygoid 2. in adults only width of the postorbital bar and orbit di- 3. never ameter (character 75). The postorbital bar 74. average ratio of inter- 0. 0.07 varies in width among the species ofthis fam- maxillary foramen length 1. about 0.20 to 0.40 ily from two times wider than the orbit to to length primary palate 2. about 0.60 one-sixth of orbit width (fig. 11). Variation 75. postorbital bar relative to 0. about 2 times or- in the width of the postorbital bar relative to orbit bit diameter the width of the orbit is not continuous but 1. about equal to or- constitutes four separate sets of species. The bit to 1/3 of orbit outgroups vary in width of 2. less than 1% of or- postorbital bar bit between state two (equal to or wider than 76. quadratojugal participates 1. no orbit) and state three (one-half to one-third in processus trochlearis 2. yes width of orbit). Only Claudius, with a very oticum narrow postorbital bar (state 4), and Platy- 77. quadrate make-up of the 1. greater than 50% sternon and the chelonioids, which lack tem- processus trochlearis oti- 2. 33 to 50% poral emargination (state 1), show the ex- cum 3. less than 33% treme conditions. In the current context it 78. proportion of processus 1. 15.6%orless seems most appropriate to consider most di- trochlearis oticum made 2. 22.1% or more vergent postorbital bar widths to be derived up by parietal relative to the combined intermediate groups. anteriorly convex dorsal margin that is usu- SKULL EMARGINATION ally formed by the prefrontals (fig. 9B, D). The advanced cryptodires (Chelomacryp- This is true for the outgroups and for some todira of Gaffhey, 1984), the Trionychoidea living species of trionychids. The remaining and Testudinoidea, have highly developed trionychids show some degree of emargina- temporal emargination. But these two super- tion of the prefrontals and thus alteration of families differ greatly in the degree of cheek this primitive shape of the external narial emargination that they exhibit. opening. With one exception emargination As reviewed by Gaffney (1 979b) there has occurs laterally and is either shallow (fig. 9A) always been a problem identifying landmarks 30 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 186

TABLE 11 Character States for Characters of the Trionychid Skull Useful in Assessing Intrafamilial Relationships" Characters Species 32 34 36 41 48 49 53 54 58 59 60 64 65 68 69 70 71 72 73 74 75 76 78 aubryi 1 3 2 2 2 2 4 2 2 1 3 1 1 2 2 - 1 2 1 1 1 1 1 bibroni 1 3 1 1 1 1 2 1 1 1 2 1 3 3 1 0 2 1 2 1 1 1 1 cartilagineus 1 1 1 2 2 2 2 1 1 1 2 2 1 2 1 0 2 1 3 1 1 2 1 elegans 1 3 1 1 2 2 3 2 2 1 3 1 1 1 2 - 1 2 2 1 1 2 2 euphraticus 1 1 1 2 1 1 2 1 1 1 3 2 1 1 1 0 1 1 3 2 1 2 2 ferox 1 1 1 3 1 1 2 1 1 1 3 1 1 1 1 0 1 1 3 2 1 2 2 formosus 2 3 1 2 2 2 2 1 1 1 3 3 1 1 1 1 1 1 3 1 1 1 1 frenatum 1 3 2 1 2 2 4 2 2 1 3 1 2 3 2 - 1 2 2 1 1 2 1 gangeticus 1 1 1 2 2 2 2 1 1 1 3 3 1 1 1 1 1 1 2 1 1 2 1 hurum 1 2 1 3 2 2 2 1 1 1 3 3 1 1 1 1 2 1 3 1 1 1 1 indica 1 3 2 1 1 1 2 1 1 1 2 1 2 3 1 0 3 1 3 0 0 1 1 leithii 2 2 1 2 2 2 2 1 1 1 3 3 1 1 1 0 1 1 3 1 1 1 1 muticus 2 2 1 3 1 2 2 1 1 1 3 1 1 1 2 - 1 1 2 2 2 2 2 nigricans 2 1 1 2 2 2 2 1 1 1 2 3 1 3 1 1 1 1 3 1 1 1 2 punctata 1 2 1 1 2 1 2 2 2 1 3 1 1 2 1 1 1 1 1 1 1 1 1 senegalensis 1 3 2 2 1 1 3 2 2 1 3 1 1 3 2 - 1 2 1 1 1 1 1 sinensis 2 2 1 3 2 2 2 2 1 2 3 3 1 1 1 2 1 1 3 1 1 2 1 spiniferus 1 1 1 3 1 1 2 1 1 1 3 2 1 1 2 - 1 1 3 2 2 2 2 steindachneri 1 3 1 3 2 2 2 1 1 2 3 3 1 1 2 - 3 1 3 1 2 1 1 subplanus 1 2 1 3 2 2 2 1 1 2 3 2 1 1 1 - 1 1 2 1 2 2 1 swinhoei 2 1 1 2 1 1 2 2 1 1 3 1 1 1 1 0 1 1 3 2 1 2 2 triunguis 1 1 1 3 2 2 2 1 1 1 3 1 1 1 1 0 1 1 2 1 ? 2 2 a Numbers refer to character states outlined in table 10. suitable for making comparisons of emargi- problematical. All trionychids have very deep nation between taxa. The use of exposed ele- temporal emargination that leaves the pro- ments seems to be most appropriate, but use cessus trochlearis oticum fully exposed, and of exposure of the postorbital as an index of the communication of the fossa temporalis temporal emargination in trionychids is dorsalis with the fossa temporalis ventralis is

TABLE 12 States of Skull Characters Important in Interfamilial Analysesa Characters Taxa 31 33 35 37 38 39 40 43 44 45 46 47 50 52 55 56 57 61 77 Trionychidae 3 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 3 Carettochelys 1 1 1 2 1 2 1 2 2 1 2 2 2 2 2 2 2 2 2 Staurotypus 1 1 1 1 1 2 1 2 1 1 1 2 1 1 2 1 2 2 2 Claudius 1 1 12 1 2 1 1 1 2 1 1 2 1 2 2 1 Kinosternon 1 1 1 1 1 2 1 2 1 1 1 1 1 1 2 1 2 2 2 Dermatemys 2 1 1 1 1 2 1 2 1 1 1 1 1 1 2 1 2 2 3 Cheloniidae 3 1 1 1 1 2 2 1 1 1 1 1 1 2 1 1 1 2 2 Chelydridae 3 1 1 2 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 Platysternon 1 1 1 2 1 2 1 1 1 1 1 1 1 1 1 1 1 1 1 Emydidae 2 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 Testudinidae 2 1 1 2 1 1 1 1 1 1 1 1 1 2 2 1 1 1 1 Pleurodira 3 1 1 1 1 1 3 1 1 1 1 1 3 1 2 1 1 2 a Numbers represent the character states listed in table 10. 1 987 MEYLAN: TRIONYCHIDAE 3 1 A

B D

Fig. 9. Frontal views of the skull of four cryptodiran turtles showing fusion of the premaxillae (stippled) in trionychids (A, B) and carettochelyids (D), exclusion of the premaxillae from the apertura narium extemum in trionychids (A, B), and slight (A) to extensive (B) emargination of the anterior border of the prefrontals. A. Trionyx cartilagineus (RH 129); B. T. ferox (AMNH 129737); C. Chelonia mydas (UF 55880); D. Carettochelys insculpta (UF 43888). visible over a significant distance. With this the postorbital from the temporal emargi- degree of temporal emargination the post- nation might seem quite primitive and it cer- orbital bone, which makes up a significant tainly is if isolation is via parietal-squamosal portion of the postorbital bar, is usually ex- or parietal-squamosal-quadratojugal contact. posed. This is true for all outgroup triony- But isolation via jugal-parietal contact is a choids and testudinoids examined. The post- derived feature found only among triony- orbital in trionychids is one of several skull chids. Jugal-parietal contact on the skull sur- elements which has undergone extreme re- face can vary within a single trionychid duction. This reduction is so extreme that species. This variable condition is considered contact between the jugal and parietal occurs to be intermediate between the primitive ab- below the skull surface in all trionychids sence of jugal-parietal contact on the skull (character 35, table 12) and these two ele- surface and its presence which is certainly ments make up much of the postorbital bar. derived (character 34, table 11). In some trionychids jugal-parietal contact is Lateral to the temporal emargination in so strong that it is present on the skull surface trionychids is a very narrow bar formed by and the postorbital is isolated from the tem- the jugal and quadratojugal. The trionychids poral emargination (fig. 1 1A, B). Isolation of parallel the condition seen in some emydids 32 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 186

TABLE 13 Autapomorphic Skull Features of Trionychid A Turtles Char- acter Species Autapomorphic state 42 Cyclanorbis apertura narium externum elegans medially emarginate 46 Trionyx basisphenoid fails to con- euphraticus tact palatines 51 Pelochelys vomer contacts basisphe- bibroni noid 62 Trionyx maxillae contact frontals in subplanus orbit 63 Trionyx pterygoid isolated from ex- B triunguis occipital by basioccipital 66 Cycloderma vomer is absent frenatum 67 Cycloderma jugal excluded from orbit aubryi 74 Chitra indica foramen intermaxillaris quite reduced 75 Trionyx postorbital bar one-ninth of subplanus orbit diameter

of extreme quadratojugal reduction. But unlike the case in emydids this element is never lost. In all trionychids the quadratojugal con- Fig. 10. Anterior view of the skulls of two tacts only the jugal and not the maxilla or trionychid turtles. A. Trionyx triunguis (BMNH postorbital anteriorly. Posteriorly it sutures 1947.3.6.12); B. Cyclanorbis senegalensis (BMNH to the quadrate and squamosal. In other liv- 65.5.9.20); both from Loveridge and Williams ing trionychoids the contact of the quadra- (1957). tojugal to the postorbital is maintained and the quadratojugal maxillary contact is maintained except in some Dermatemys (UF tudinoids, on the contrary, cheek emargina- 29168; fig. 172 in Gaffney, 1979b). Reduced tion is quite well developed and extends well contact of the quadratojugal is considered de- dorsal to such a line (except in Malayemys). rived within the Trionychoidea (characters In all testudinoids and trionychoids except 31 and 33, table 12). for the Trionychidae, cheek emargination is Because of the reduced size of the qua- limited anteriorly by the maxillary. In the dratojugal, the jugal and squamosal lie quite Trionychidae, cheek emargination occurs close to one another in all trionychids. In six within the jugal when it is present (character species they are occasionally in contact. This 40, table 12). Because of flexure of the snout is considered to be a derived condition (char- in trionychids, ventral emargination of the acter 32, table 11). jugal does reach above the lower rim of the Strong cheek emargination, which accom- orbit in a few cases. But emargination occurs panies temporal emargination in testudi- only within the jugal and is the site of origin noids, is not found among living triony- ofthe M. zygomatico-mandibularis (Dalrym- choids. Although cheek emargination is ple, 1977), a muscle which is unique to trion- visible in Dermatemys, Carettochelys, and ychids. Therefore, it is likely that cheek emar- kinostemids, it does not extend above a line gination in trionychids is not homologous to extending horizontally from the lower edge that of other turtles and that restriction of of the orbit (character 39, -table 12). In tes- true cheek emargination ventral to the lower 1987 MEYLAN: TRIONYCHIDAE 33

Fig. 11. Dorsal view of the skulls of three trionychid turtles. Top, Trionyx triunguis (BMNH 1947.3.6.12), from Loveridge and Williams (1957); middle, Chitra indica (from Gray, 1855, presumably BMNH specimen, sutures added from MCZ 29487); bottom, Cyclanorbissenegalensis(BMNH 65.5.9.20), from Loveridge and Williams, 1957). 34 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 186

TABLE 14 the prootic or parietal (character 61, table Average Contribution of Quadratojugal, Quadrate, 12). These features are important at the fam- Prootic, and Parietal to the Processus Trochlearis ily level, there is little variation within the Oticum of Recent Trionychid Turtles Trionychidae. Qua- drato- Quad- Pari- PROCESSUS TROCHLEARIS Species N jugal rate Prootic etal OTICUM AND QUADRATE aubryi 8 0.000 0.227 0.607 0.166 The bibroni 7 0.000 0.207 0.602 0.117 processus trochlearis oticum is a dis- cartilagineus 7 0.007 0.239 0.655 0.139 tinctive feature of the Cryptodira. It is over elegans 5 0.011 0.236 0.565 0.221 this structure that the majority of the jaw euphraticus 9 0.020 0.166 0.557 0.266 adductor musculature lies. This is in contrast ferox 11 0.032 0.290 0.396 0.260 to the condition in Pleurodira in which the formosus 4 0.000 0.294 0.635 0.071 lower jaw adductors slide over a process of frenatum 4 0.026 0.130 0.734 0.136 the pterygoid. In most cryptodires the ma- gangeticus 7 0.007 0.137 0.720 0.144 jority of the processus is formed by the quad- hurum 6 0.000 0.213 0.744 0.054 rate. indica 8 0.000 0.312 0.626 0.062 In leithii 3 0.000 0.249 0.684 0.091 trionychids the processus trochlearis muticus 5 0.027 0.072 0.581 0.320 oticum can be quite large and always involves nigricans 1 0.000 0.200 0.500 0.292 the quadrate, prootic, and parietal (table 14). punctata 6 0.000 0.192 0.717 0.094 In 13 species the quadratojugal is included senegalensis 6 0.000 0.177 0.671 0.152 in at least some individuals (fig. 11 top). sinensis 9 0.005 0.154 0.728 0.122 Within the Trionychidae, three useful pat- spiniferus 8 0.019 0.262 0.527 0.225 terns of variation are noted: the inclusion of steindachneri 1 0.000 0.180 0.819 0.000 the quadratojugal in the processus trochlearis subplanus 6 0.088 0.180 0.625 0.112 oticum, reduction in the contribution made swinhoei 1 0.033 0.100 0.500 0.300 the and triunguis 10 0.004 0.189 0.584 0.223 by quadrate, increase in the contribution made by the parietal. The first occurs when the quadratojugal sends a medial process rim of the orbit can be considered a derived across the anterior edge of the quadrate feature of the Trionychoidea (character 39, (fig. 11 top). It results in reduction of the table 12). quadrate contribution and is absent from all outgroups. It is thus considered to be derived STAPEDIAL FORAMEN within the Trionychidae (character 76, table 11). In trionychids, unlike essentially all oth- The most significant difference between er the testudinoid cryptodires, quadrate makes up less and trionychoid turtles is in the than one-third ofthis structure (character 77, pattem ofblood flow to the head (McDowell, table 1961; 12). Albrecht, 1967; Gaffney, 1975, 1979b). There is additional variation among trion- This is reflected in variation of the size of the ychids in the amount ofparietal contribution. stapedial foramen and in the morphology of In the the majority the parietal contribution is prootic and parietal adjacent to this fo- small, always less than one-sixth of the total ramen. In testudinoids the majority of an- (table 14). In the North American forms, and terior blood flow is via the stapedial artery. also Therefore Cyclanorbis elegans, Trionyx euphrati- the foramen stapediotemporale is cus, T. nigricans, T. swinhoei, and T. triun- large and there is often a groove in the prootic the parietal and parietal for the large guis contribution is slightly larg- stapedial artery. In er, about one-fourth or more ofthe processus trionychoids, the stapedial artery is reduced trochlearis oticum (character 78, table because most of the anterior blood 1 1). flow is via The contribution of the parietal to this struc- the internal carotid artery. In this superfam- ture in other ily the foramen cryptodires is quite limited or stapediotemporale tends to absent. Thus the large contribution in trion- be reduced or absent and rarely is there evi- ychids is clearly derived. dence of a groove for the stapedial artery on In very few chelonians does the quadrate 1987 MEYLAN: TRIONYCHIDAE 35

A processus inferior parietalis

foramen nervi trigemini pa

fossa cartilaginis epipterygoidei processus pterygoideus externus B foramen stapedio-temporale

fo n t pforamen ner trigemini

processus interfenestralis f canalis aavernosus | ~~~~~~processus trochlearis pterygoidei fenestra ovalis

foramen stapedio-temporale z _ _ _ > L _ ~~~~~~~~~~processustrochlearis oticum

processus~nervifetrigemini~ ~ ~~~~~~~~~~frae

processufenstrintrfnesrsisnltqueno

Fig. 12. Right lateral views of the skull of three cassichelydians with portions removed to expose trigeminal region. A. Solnhofia parsoni (Teyler Museum 4023); B. Emydura sp. (AMNH 72418); C. Chelydra serpentina (AMNH 9249). 36 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 186 A E

B F

C G

D H

Fig. 13. The trigeminal region of eight trionychoid turtles showing contacts of the skull elements around the foramen nervi trigemini anld participation by the palatine in the lateral wall of the braincase. The foramen interorbitale is crosshatched; the foramen nervi trigemini is stippled. Abbreviations: e, epipterygoid; pal, palatine; pa, panietal; pr, prootic; pt, pterygoid; qu, quadrate. A. Dermatemys mawEi (BMNH 191 1.1.28.1); B. Staurotypus salvinji (BMNH 1879.1.7.5); C. Carettochelys inscuipta (BMNH 1903.4.10.1); D. Lissemyspunctata (UF 56017); E. Cyclanorbis elegans (BMNH 1954.1.14.3); F. Trionyx hurum (BMNH 86.8.16.2); G. Trionyx triunguis (BMNH 62.3.20.8); H. Chitra indica (IRSNB 3295). 1987 MEYLAN: TRIONYCHIDAE 37 completely surround the columella (Gafiney, TABLE 15 1979b). Among cryptodires this occurs in the Fusion of the Epipterygoid to the Pterygoid in Trionychidae, Carettochelys, Chelydridae, Trionychid Turtlesa and most Testudinidae (tables 10, 12). Species N A B C aubryi 7 94.5 88.0 122.0 TRIGEMiNAL REGION bibroni 7 119.0 119.0 119.0 cartilagineus 7 131.5 none 131.5 The trigeminal foramen lies lateral to the elegans 5 125.0 122.0 130.0 braincase and ventral to the processus troch- euphraticus 9 83.3 none 83.3 learis oticum of cryptodires (figs. 12, 13). In ferox 9 110.0 none 110.0 trionychids it is a large opening providing an formosus 4 79.0 none 79.0 exit for the maxillary and mandibular frenatum 4 107.3 134.0 134.0 branches of the trigeminal nerve as well as gangeticus 7 110.0 111.0 111.0 the mandibular artery (Gafffiey, 1979b). In hurum 4 99.0 none 99.0 trionychids the parietal, prootic, quadrate, indica 8 195.0 none 195.0 leithii 3 108.0 none 108.0 pterygoid, and epipterygoid may contact this muticus 3 39.5 41.5 41.5 foramen but there is significant inter- and nigricans 1 105.0 none 105.0 intraspecific variation in the degree and form punctata 6 50.0 38.0 81.5 of contact of each element (fig. 13). senegalensis 6 80.3 75.0 117.5 An epipterygoid is present in all trionychid sinensis 9 58.5 none 58.5 species but tends to fuse to the pterygoid in spiniferus 8 59.5 none 59.5 larger individuals (table 15). Fusion occurs steindachneri 1 43.8 none 43.8 less frequently (perhaps later in life) in trion- subplanus 4 61.6 104.5 104.5 ychines than in cyclanorbines. Variation in swinhoei 1 67.0 none 67.0 10 153.0 143.5 153.0 the length of retention of a distinct epipter- triunguis ygoid is treated via three states of character a Condylar length (in mm) of the largest skull with a 73 (tables 10, 1 1). This element usually fuses free epipterygoid (A), the smallest skull with a fused to the pterygoid in older adults of most cryp- epipterygoid (B), and largest skull measured (C) are given todires. Long-term retention of the epipter- for each species. ygoid is therefore considered to be a derived feature. Because the epipterygoid is an important tween the prootic and epipterygoid (state 1) landmark in describing variation in the mor- (fig. 13B, D, F), ventrally between the epi- phology of the trigeminal region of triony- pterygoid and quadrate (state 0), anteriorly chids, descriptions of this region are based between the parietal and epipterygoid (state on individuals in which this element is not 2), or in no individuals at all (character 69, yet fused to the pterygoid. The contacts de- state 2) (fig. 13E, G). See table 11 for distri- scribed are those visible on the outside of the bution of these character states. skull (as seen in fig. 13); in some cases internal Contact of the pterygoid to the foramen contacts will differ. Complication ofthese de- nervi trigemini between the prootic and epi- scriptions arises because the epipterygoid is pterygoid (state 1, character 70) occurs in Tri- a superficial element of variable shape and onyx formosus, T. gangeticus, T. hurum, T. size that can cover certain contacts in some nigricans, and Lissemys punctata and results individuals of a given species but not in oth- in the isolation of the quadrate from the fo- ers. This results in the ungainly appearance ramen nervi trigemini (fig. 1 3D, F). In both of the three states of character 70 (table 10) Cyclanorbis species and both Cycloderma in which all states include the possibility of species the quadrate is also isolated from the no pterygoid-trigeminal contact (the case foramen nervi trigemini. But in this case it when the epipterygoid is large), but show dif- is the epipterygoid that meets the prootic pos- ferent forms of pterygoid-trigeminal contact teriorly and thus intervenes (character 71, if the epipterygoid is not enlarged. When the state 2; fig. 1 3E). When the epipterygoid fuses pterygoid does contact the foramen nervi tri- to the pterygoid, the two groups mentioned gemini the contact may occur posteriorly be- above (those with state 1 of character 70 and 38 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 186

those with state 2 of character 71) look iden- facilitates blood flow through the internal ca- tical. rotid in trionychoids. Significant variation in this region among The location of the foramen posterius ca- the outgroups makes assigning polarities to nalis carotici interni in the Trionychidae is characters of contact of the epipterygoid to also of some interest. In all species of this the foramen nervi trigemini difficult. Iden- family it is completely surrounded by the tification of polarity for other contacts in the pterygoid (figs. 14D-F, 1 5A, C). The same is trigeminal region seems clear. In no other true for Carettochelys, but in kinostemnids it trionychoid does the epipterygoid contact the can be open dorsally to the fenestra postotica prootic posteriorly (fig. 1 3A, B, D) as it does (Staurotypus) or be bordered dorsally by the in Cyclanorbis and Cycloderma (character 71, prootic (Kinosternon and Sternotherus, fig. table 11; fig. 13E) or anteriorly as it does in 14C). In Dermatemys and in most testudi- some or all members of certain trionychine noids and chelydrids it is open dorsally to the species (character 71, table 1 1; fig. 1 3H). Sim- fenestra postotica (character 56, table 12; fig. ilarly, all trionychoid outgroups have contact 14A, B). between the epipterygoid and palatine (fig. In some trionychids the foramen posterius 13A-C) and the absence of this contact in canalis carotici intemi is quite ventrally lo- some or all members of a species is consid- cated and is reminiscent of the condition in ered derived (character 68, tables 10, 11). the "Paracryptodira" (fig. 1 5C). However, in An important feature ofthe Trionychoidea all other trionychoids and other Eucryptodira (sensu Gaffiey, 1979b) is participation ofthe it is posteriorly located. Thus the presence of palatine in the formation of the lateral wall these foramina on the ventral surface of the of the braincase. This occurs in all triony- skull is considered derived. choids examined and can be seen just ante- Variation in the location of the foramen rior to the foramen nervi trigemeni (fig. 13). posterius canalis carotici interni within the In trionychoids the pterygoid is excluded from Trionychidae is best described in relation to the interorbital fenestra by the expanded pal- a crest of bone which is a lateral extension of atines. In testudinoids and in other turtles the tuberculum basioccipitale. In no member the pterygoid either reaches the interorbital of this family is this foramen located above fenestra or is immediately adjacent to it such a crest, but in Pelochelys bibroni, Chitra (character 43, table 12) (fig. 12). indica, Trionyx cartilagineus, and T. nigricans (only one specimen available) it is found within the crest (see fig. 15; foramen posterior OccnrrAL REGION canalis carotici interni is visible in A and C but not in B). The latter condition is consid- There are numerous systematically useful ered to be primitive relative to the ventral characters visible on the skull in posterior position found in all other species (character view. One of these is a reflection of the im- 60, table 1 1). portance of the internal carotid artery (Al- The foramen jugularis posterius is located brecht, 1967; McDowell, 1961; Gafffey, lateral to the foramen in 1975, 1979b). The large magnum turtles and diameter of the ca- is visible in posterior view. In most crypto- nalis carotici interni and the straight path that dires it is surrounded by the exoccipital or it follows in trionychoids can be observed exoccipital and even in opisthotic (fig. 14A-C). In articulated skulls. A stiffwire, slightly some cheloniids, some trionychids, narrower than the and some canal, will pass into the Claudius and Platysternon, this opening is foramen posterius canalis carotici interni and continuous with out of the the fenestra postotica (fig. foramen anterius canalis carotici 14D). Isolation of the foramen jugularis interni with ease (character 57, table 12). pos- In terius from the fenestra postotica when pres- large trionychids the latter opening is clearly ent in the visible through the Trionychidae occurs in a unique former. This is in contrast manner: that contact to the case in other cryptodires in is, by of the pterygoid which this to the opisthotic (fig. 14E, F). In all cycla- canal makes an S-shaped curve or a high- norbines the angle bend (see figs. pterygoid arches dorsally to meet 25-29 in Gaffney, 1979b). the opisthotic (fig. 1 4F). the It seems likely that this straight, wide In trionychines, path infrequent isolation occurs via the descent of 1 987 MEYLAN: TRIONYCHIDAE 39

I foramen jugulare posterius foramen posterius canalis carotici interni

posterius jugulare foramen I foramen posterius canalis carotici interni fenestra postotica Fig. 14. Posterior views ofthe skull of six eucryptodiran turtles. A. Macroclemys temminckii (AMNH 58251); B. Chinemys reevesi (AMNH 31117); C. Sternotherus odoratus (AMNH 69752); D. Pelochelys bibroni (AMNH 23541); E. Pelodiscus sinensis (UF H 2406); F. Lissemys punctata (NMNH 61094). 40 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 186 a narrow process of the opisthotic across an apertura nanum intemum and the posterior otherwise open fenestra postotica (fig. 14E). limits of the foramen intermaxillaris remain These two types of isolation of the foramen undefined. jugulare posterius appear to be independent A structure that appears to be homologous evolutionary events (Loveridge and Wil- to the foramen intermaxillaris is present in liams, 1957) and are treated as such in the mature individuals of all three living stau- analysis of intrafamilial relationship (char- rotypine kinostemids and in Xenochelys for- acters 58 and 59, table 11). mosus (Oligocene of South Dakota, Wil- In nearly all trionychids, as in most other liams, 1952). The deep pit in the premaxillae, trionychoids and in chelydrids (including which accommodates the symphyseal pro- Platysternon) and chelonioids, there is con- jection of the lower jaw in all kinosternids, tact between the exoccipital and pterygoid. opens dorsally in large individuals of both Only in Trionyx triunguis does the basioc- species of Staurotypus, in Claudius, and in cipital intervene between these elements, Xenochelys. This does not occur in large in- separating them as it does in most testudi- dividuals of any other living turtles with noids. In the current context this is a unique strongly hooked lower jaws such as chely- feature most useful for the recognition of T. drids (including Platysternon). In staurotyp- triunguis (character 63, table 13). Separation ines, this opening accommodates the sharply of the pterygoid from the exoccipital may be hooked symphysis ofthe lowerjaws as it does a shared derived feature of the Testudinoi- in Carettochelys. Trionychids always have the dea. foramen intermaxillaris in spite of the fact The basis tuberculi basalis is a small tu- that they have unhooked lower jaws (char- bercle on the dorsal surface of the basioccip- acter 47, table 12). ital found within the braincase. When present Variation in the size of the foramen inter- this tubercle is visible (under correct lighting) maxillaris among trionychids has been uti- through the foramen magnum. Gaffney lized by several authors (Loveridge and Wil- (1 979b) reported that it is variably developed liams, 1957; De Broin, 1977). Comparison in most turtles but that it is missing in Tri- of the length of the foramen intermaxillaris onyx ferox. I find this structure to be absent relative to the total skull length is not satis- in all trionychoids and testudinids examined, factory; the distribution of this character for but clearly visible in cheloniids, dermoche- trionychids is quite continuous (fig. 2). It lyids, chelydrids, and emydids (but not Rhi- should be noted, however, that the members noclemmys pulcherrima). This is therefore a of a proposed monophyletic group (Meylan, useful character at the interfamilial level 1985), the North American forms plus Tri- (character 55, table 12). onyx swinhoei, T. euphraticus, and T. triunguis, have the highest values for the ratio of foramen intermaxillaris length to total skull length. PALATE This character can be utilized if examined The most striking differences between the in terms of foramen size relative to the pri- palates oftrionychids and those ofother cryp- mary palate. Variation in the ratio of length todires is the presence of a median foramen of the foramen intermaxillaris to length of anterior to the apertura narium intemum and the primary palate among trionychids falls the presence of unconstricted pterygoids (fig. into five distinct groups (fig. 2, table 10). 15). This midline opening is usually of large Identification of a character polarity for the size and is called the foramen intermaxillaris. states of this character is difficult. The fora- It varies in size in the Trionychidae (see be- men intermaxillaris in other trionychoids is low, character 74) but it always separates the highly specialized in one case (Carettochelys) vomer from the fused premaxillae. The same and incompletely developed in the other structure appears to be present in Carettoche- (Staurotypinae). It appears prudent to as- lys where it is continuous with the apertura sume that the medium size classes together narium intemum. In Carettochelys the vomer approximate the primitive state and that the and maxillae do not meet anterior to the most divergent conditions (states 0 and 2) are 1 987 MEYLAN: TRIONYCHIDAE 41

Fig. 15. Ventral view of the skulls of three trionychid turtles. Top, Trionyx triunguis (BMNH 1947.3.6.12, modified from Loveridge and Williams, 1957); middle, Chitra indica (from Gray, 1855, presumably BMNH specimen, sutures added from MCZ 29487); bottom, Cyclanorbissenegalensis(BMNH 65.5.9.20, from Loveridge and Williams, 1957). 42 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 186 derived within the Trionychidae (character terior extension of the latter in trionychids 74, tables 11, 13). comes a greater possibility that such contact The vomer is one ofseveral elements which might occur. Siebenrock (1897) reports vo- is reduced in the Trionychidae. In most tur- mer-basisphenoid contact on the dorsal sur- tles it lies between the paired maxillae and face of the palate in Pelochelys. In two of the palatines. Anteriorly it reaches the premax- seven Pelochelys skulls examined during this illae and posteriorly it often contacts the study (USNM 231523 and NMW 1857), con- paired pterygoids. When a foramen inter- tact between these elements is present on the maxillaris is present, premaxillary contact is palate. This condition is unique to Pelochelys prevented. In some trionychids the vomer among the Trionychidae (character 51, table divides the maxillae completely and reaches 13). In Cycloderma frenatum the vomer is the foramen intennaxillaris between them (fig. absent. This is a unique condition among 15C). This most closely approximates the trionychids (character 66, table 13). condition in the outgroups in which no fo- At or near the palatine-pterygoid suture in ramen intermaxillaris is present and is there- all chelonians is located a paired ventral fore considered to be the primitive condition opening in the palate, the foramen palatinum for the relationship of the vomer to the max- posterius. This opening is never large in illae (character 48, table 11). trionychids (fig. 15). It may be entire, divided In other trionychids the maxillae meet on into two openings, or divided into numerous the midline of the palate ventral to the vo- small openings not larger than the nutritive mer. Depending on the degree of reduction foramina of the palate. Small size of these of the vomer and the length of this inter- openings may be a feature shared by all trion- maxillary suture, the vomer may still enter ychoids as well as some testudinoids, but the the foramen intermaxillaris by reaching it variation in the division of this opening is dorsally over the united maxillae. Reduction useful within the Trionychidae, and in par- of the vomer to the extent that it does not ticular among the Cyclanorbinae (character reach anteriorly to the foramen intermaxil- 53, table 1 1). Division of the foramen pala- laris is interpreted as the derived state of tinum posterius is considered derived. character 49 (table 11). The contacts of the foramen palatinum Posteriorly, the vomer ofmost cryptodires posterius also vary among the living species reaches between the paired palatines as far as of the Trionychidae. In most trionychids, as the pterygoids. This is true of Dermatemys in most chelonians, these foramina contact and kinosternids, but not Carettochelys or the palatine and the pterygoid and/or max- any trionychids (fig. 15). The failure of the illary. In a limited number oftrionychids this vomer to reach as far posterior as the pter- opening is restricted to the palatine, which is ygoids is considered a derived condition considered to be a derived condition (char- (character 50, table 12). acter 54, table 11). In most chelonians the vomer is the only The processus pterygoideus externus of unpaired midline element reaching the trans- cryptodires usually takes the form of a mod- verse pterygoid-palatine suture. In Caret- erate to short posterior or posterolateral pro- tochelys and all trionychids (except T. eu- jection from the anterolateral edge of the phraticus), only an enlarged basisphenoid does pterygoid just anterior to some degree of me- so (fig. 15). This unique contact of palatal dial constriction. It is found in nearly all cryp- elements has been recognized as evidence of todires and varies considerably in degree of unique common ancestry of these two taxa development. In trionychids there is no me- (Baur 189 lb; Meylan, 1985). It is treated as dial constriction ofthe pterygoids and no free such here (character 46, table 12). The ab- projection of this process (fig. 15). In Caret- sence of contact of palatines and basisphe- tochelys, the pterygoids are only slightly con- noid in most specimens of T. euphraticus ap- stricted and the processus pterygoideus ex- pears to be a unique reversal (character 46, ternus projects very weakly or not at all. In table 13). other trionychoids these processes may be The vomer of turtles does not normally present (Kinosternon, Staurotypus, some contact the basisphenoid, but with the an- Dermatemys, some Claudius) or absent (some 1 987 MEYLAN: TRIONYCHIDAE 43

Claudius, some Dermatemys, Xenochelys), lower jaw, the characters treated in this sec- but they are never as large and posteriorly tion are most valuable in determining inter- projecting as in the Chelydndae or some of familial relationships of trionychids. The the Emydidae. Reduction of this projecting hyoid and lower jaw are also important at quality could be a shared derived feature of this level but prove to be of additional value the Trionychoidea. It occurs elsewhere among in the study of intrafamilial relationships. the Cheloniidae (Chelonia), "Bataguridae" (Malayemys), and Testudinidae (several genera). The absence of a projecting processus is MANDIBLE certainly derived for the Trionychidae and The lower jaw of trionychids is remarkable possibly for the Trionychidae plus Caret- for its very high coronoid processes and large tochelys (character 52, table 12). retroarticular processes (Boulenger, 1889) and The elongate basisphenoid of trionychids for the significant contribution to the area varies in shape. In most species, as in the articularis mandibularis made by the suran- outgroups, it has a subtriangular shape al- gular (compare figs. 16 and 17). The retroar- though it is usually somewhat more elongate. ticular process is much larger than that of In a few forms medial constriction of the ba- other turtles (except Carettochelys) and adds sisphenoid occurs either occasionally or fre- 10 percent or more to the total length of the quently. The presence ofan hourglass shaped jaw (character 99, tables 16, 18). basisphenoid is considered derived within the As observed by Gaffiney (1 979b), the prear- Trionychidae (character 64, table 11). ticular and surangular of trionychids are frequently in contact, restricting or subdividing the fossa meckelii (fig. 17, top). In 82 percent VARIATION IN THE (81/98) of the trionychids examined the VISCERAL SKELETON AND prearticular and surangular meet either on NONSHELL POSTCRANIA the posterior edge of the fossa meckelii (36/ Although the nonshell postcranial ele- 98) or divide it by meeting across the middle ments of turtles have been shown to provide (45/98). There is no clear pattern of variation valuable systematic data and are important among the species within the family. All 3 in currently used arrangements, they have not conditions occur in three taxa; 2 of 3 con- been used extensively. The most important ditions occur in 1 1 others. The high incidence modem studies of the systematic value of of surangular-prearticular contact across the nonshell postcrania are found in Williams fossa meckelii could be considered a shared (1950) and Zug (1971). Williams' (1950) derived feature of the family Trionychidae. monograph on the cervical articulations of However, it occurs in several other taxa and turtles forms the foundation of the most fre- absence of a clear distribution makes this quently used modem classifications of turtles character unusable. In Carettochelys one-half (see discussion). Zug (1971) provided data on of the specimens (N = 4) examined show this the pelvic girdle and hind limbs which has contact. Elsewhere among cryptodires it oc- since been cited as evidence for the recent curs in some Kinosternon, in Dermatemys, in realignment of certain cryptodires (Gaffney, Platysternon, and in some pleurodires. 1975, 1984). In most turtles the area articularis man- In the current attempt to determine the dibularis is made up by the articular with best hypothesis of relationships for triony- little or no contribution from the surangular chids, data from the cervical and thoracic (fig. 16, top). Only in the Trionychidae and vertebrae, the hyoid, and the pelvic and pec- Carettochelys does the surangular make up toral girdles have been found to be extremely one-half or more of this surface (fig. 17, top). valuable. Characters of the appendages and The surangular is always included in this area caudal vertebrae are of less use. The visceral in other trionychoids but always forms less skeleton has been included with the other than half of the articular surface. In testudi- nonshell postcrania in an effort to balance the noids and chelydrids the surangular is fre- size of the three osteological data sets. quently absent from the area articularis man- With the exception of the hyoid and the dibularis and when present contributes less 44 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 186

TABLE 16 TABLE 16-(Continued) Systematic Characters and Character States of the Character Lower Jaw and Nonsheli Postcrania of Trionychid Turtles Characters states 97. foramen 1. no Character nervi auriculotem- with one lateral and 2. yes Characters states poralis one dorsal opening 79. entepicondylar foramen open 1. no 98. foramen intermandibularis 1. sometimes along humerus 2. variable caudalis enclosed by preartic- 2. never 3. yes ular 80. hyperphalangy of manus dig- 1. no 99. retroarticular process large, 1. no its 4 and 5, pes digit 4 2. yes about one-tenth of total low- 2. yes 81. radius and ulna in contact 1. no er jaw adjacent to manus 2. yes 100. ilia curve medially 1. no 82. number of clawed digits of 1. 5 2. yes manus 2. 3 or fewer 101. ilia curve posteriorly 1. no 3. 2 or fewer 2. yes 83. cervical centra 2-7 opistho- 1. no 102. ilia anteroposteriorly expand- 1. yes coelus 2. yes ed at distal end 2. no 84. centra of 8th cervical and 1st 1. yes 103. thelial process present 1. no body vertebrae in contact 2. no 2. yes 85. ventral process on 8th cervi- 1. present 104. pubis and ischium closely 1. no cal 2. absent opposed or in contact across 2. yes 86. ventral process on 8th cervi- 1. single thyroid fenestra cal 2. double 105. epipubic region ossifies 1. yes 87. ventral keel on 8th cervical 1. no 2. no present and limited to poste- 2. yes 106. pectineal processes and inter- 1. no rior end pubic suture lie in a single 2. yes 88. strong dorsal processes on 1. no plane cervicals 2. yes 107. ischia extend into thyroid fe- 1. yes 89. number of posterior body 1. 0 nestra 2. no vertebrae with transverse 2. 1 108. pectineal processes equal to 1. no processes not reaching pleu- 3. 2 or wider than interpubic con- 2. yes MIs tact 90. number of ossifications in 1. 1 109. metischial processes present 1. yes corpus hyoidis 2. 6 and distinct 2. no 3. 8 110. ilioischial notch 1. absent 91. number of ossifications in 1. 1 only 2. present comu branchiale II 2. 2-6 111. coracoid shortest of three 1. no 3. 7 or more pectoral processes 2. yes 92. ossifications of comu bran- 1. no 112. angle of acromion process to 1. no chiale II broad and strongly 2. yes scapula approaches that of 2. yes sutured coracoid to acromion 93. basihyals in close contact and 1. no 113. coracoid longest of three pec- 1. no projecting anteriorly 2. yes toral processes 2. yes 94. surangular forms part of area 1. less than 1/2 articularis mandibularis to 0 2. less than 1/2 3. greater than than half the articular area. The large con- or equal to 1/2 tribution by the surangular in trionychids 95. symphyseal ridge strong and 1. no must be considered derived. The condition present in a depression 2. yes in other trionychoids appears to be inter- 96. foramen nervi auriculotem- 1. no mediate between the state in the Trionychi- poralis with two lateral open- 2. yes dae and that in other turtles (character 94, ings table 18). An important systematic character in the lower jaw of trionychids is the presence of a 1 987 MEYLAN: TRIONYCHIDAE 45

TABLE 17 States for Characters Found to be Useful in Hypothesizing Relationships Among Recent Trionychid Turtlesa Characters Species 95 98 100 107 109 87 88 112 113 90 91 92 93 aubryi 1 2 2 1 2 1 2 1 1 2 1 1 2 bibroni 1 1 1 2 1 2 2 2 2 3 2 2 1 cartilagineus 2 1 1 2 1 2 1 1 2 3 2 1 1 elegans 1 2 1 2 2 1 1 2 1 2 1 1 2 euphraticus 1 2 1 2 2 2 1 1 2 3 3 1 1 ferox 1 1 1 2 2 1 1 1 2 3 3 1 1 formosus 2 2 1 2 ------2 1 1 frenatum 1 2 2 1 2 1 2 1 1 2 1 1 2 gangeticus 2 1 1 2 1 1 1 1 2 2 3 1 1 hurum 2 1 1 2 1 1 1 1 2 3 1 1 1 indica 1 2 1 2 1 2 2 2 2 3 2 2 1 leithii 2 1 1 2 1 1 1 1 2 2 2 1 1 muticus 1 1 1 2 1 1 1 2 2 2 2 1 1 nigricans 2 1 1 2 1 1 1 1 2 2 2 1 1 punctata 1 2 1 1 2 1 1 1 2 2 1 1 2 senegalensis 1 2 2 2 2 1 1 2 1 2 1 1 2 sinensis 1 1 1 2 1 1 1 1 2 2 2 1 1 spiniferus 1 1 1 2 1 1 1 2 2 2 3 1 1 steindachneri 1 1 - 2 - - - - - 2 2 1 1 subplanus 2 1 1 2 1 1 1 1 2 3 2 1 1 swinhoei 1 2 - 2 - - - - - 3 - 1 1 triunguis 1 1 1 2 1 1 1 1 2 2 2 1 1 a See table 16 for explanation of characters and character states. sagittal ridge on the triturating surface at the in the surangular, representing a divided fo- symphysis (De Broin, 1977). This ridge usu- ramen nervi auriculotemporalis, is consid- ally forms within a depression on an other- ered derived (character 96, table 18). wise flat surface (fig. 17, top). Such a single Gaffney (1979b) mentioned an additional, ridge does not occur in other turtles and ap- apparently unnamed, foramen in the suran- pears to be derived within the Trionychidae. gular that communicates with the foramen Among the members of this family a ridge nervi auriculotemporalis and the fossa meck- occurs only in the Indian species, and in Tri- elii. Unlike the foramen nervi auriculotem- onyx cartilagineus and T.formosus (character poralis, it opens dorsally, not laterally. It is 95, table 17). A ridge is also present in the mentioned as occurring in Staurotypus and largest individuals of T. subplanus. Terrapene. I have noted this opening in all The foramen nervi auriculotemporalis is a kinosternids examined, and in Platysternon, single or multiple opening in the surangular but in no other taxa. The occurrence of the ventral to the area articularis mandibularis. opening can clearly be considered derived and Gaffney (1979b) reported multiple openings it appears to be a shared derived character for this foramen only in Podocnemis expansa. for the Kinostemidae (character 97, table 18). Two or more lateral openings are also present On the lingual surface of the jaw, in the in some specimens of almost every species suture between the prearticular and the an- of trionychid. Additional pleurodires (Pelu- gular, there may appear two foramina, the sios castaneus) and also some testudinoids foramina intermandibularis oralis and cau- (Cuora, Graptemys, and Geoclemys) also have dalis (fig. 16, bottom). In most turtles there multiple lateral openings in the surangular. is evidence of both. In trionychids the ante- The occurrence of multiple lateral openings rior one (oralis) is never present and the pos- 46 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 186

area articularis mandibularis

lingual

foramen intermandibularis oralis Fig. 16. Lower jaw of Chelydra serpentina (AMNH 67015). Top, dorsal view of right ramus; bottom, medial view of right ramus. Abbreviations: ang, angular; art, articular; cor, coronoid; den, dentary; pra, prearticular; sur, surangular. Symphysis is crosshatched.

terior one (caudalis) may be present or absent of either three pairs of ossifications (one pair in some species, but is always absent in others of basihyals and two pairs of basibranchials, (character 98, table 17). This uniform ab- fig. 1 8B, E), or four pairs of ossifications (an sence of the foramen intermandibularis cau- additional pair is present anterior to the ba- dalis is considered to be derived within the sihyals, fig. 18C, D, F). Cornu branchiale I Trionychidae. always consists of a single ossification while comu branchiale II consists of 1 to 18 ossifications. HyoIm Ossification of the corpus hyoidis from nu- The hyoid of most cryptodires is not an merous centers has been recognized as a elaborate structure. It typically consists of a unique feature of the Trionychidae (Sieben- single basal unit, the corpus hyoidis, which rock, 1913; Romer, 19 5 6) (character 90, table may or may not be ossified, and two pairs of 18). This highly developed structure is also branchial horns, comu branchiale I and II, known to vary among the species of the the anterior pair of which is always ossified Trionychidae (Annandale, 1912; Siebenrock, (fig. 18A). By contrast, the hyoid of triony- 1913), and characters of the hyoid appear to chids always consists of a minimum of ten be useful in assessing intrafamilial relation- ossifications and may include as many as 40 ships. (fig. 18B-F). The corpus hyoidis is composed Most members of the Trionychidae have 1 987 MEYLAN: TRIONYCHIDAE 47

foramen intermandibularis caudalis Fig. 17. Lower jaw of Trionyx cartilagineus (RH 129). Top, dorsal view, bottom, medial view of right ramus. Abbreviations are same as for figure 16. six ossifications of the corpus hyoidis six or fewer ossifications (fig. 18C-E). Only throughout life. However, in eight species the among living New World species and T. eu- corpus has six ossifications in subadults but phraticus does it always consist of seven or a total of eight ossifications at full maturity more (fig. 18F; character 91, table 17). In T. (character 90, table 17). This exceptionally gangeticus it consists of 5 to 14 centers (it = high number in these select species is con- 8.4) and in T. sinensis it consists of 3 to 9 sidered to be a further derived state. centers (F = 5.1). These two species are as- Cornu branchiale I is a single ossification signed to a group based on their average num- in all adult cryptodires examined in the course ber of ossifications. As is the case for the of this study. Cornu branchiale II, when os- corpus hyoidis, a high number of ossifica- sified, also consists ofa single element, except tions in cornu branchiale II is considered de- in some trionychids. In all of the Cyclanor- rived. binae (fig. 18B) and in most Trionyx hurum In Chitra indica and Pelochelys bibroni, (fig. 18C) it ossifies from a single center. In comu branchiale II consists of three ossifi- the remainder, it ossifies from as few as 2 to cations which are very broad and strongly as many as 18 centers. Interspecific variabil- sutured to one another (fig. 1 8D). This is a ity in the number of centers of ossification in unique condition within the Trionychidae cornu branchiale II falls into two seemingly (character 92, table 17). natural groups with two exceptions. In most The corpus hyoidis of cyclanorbine trion- Old World forms the second horn includes ychids can always be recognized by the close 48 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 186

11 contact * N _W_M___"-4_"N ___4 .4 and anterior projection of the basi- -4 hyal pair which is the .4 always anteriormost of -4 -4 three pairs of ossified elements (fig. 18B). ofthis kind do 4 .4 Projections not occur in trion- -4 ychines with six basal elements, or in the cor- 1, C * - N N - --_ _ N _ _ 1 responding elements in those species with

D eight basal ossifications. Anterior projection cc of the bony corpus is therefore considered derived for the Cyclanorbinae (character 93, C --w 0 * N _.-I --A -." -.4 -.4 ..I -4 -.4 table 17). 0 4) AND BODY PC ,0 CERVICAL VERTEBRAE N N ______N - N I 4) 4) As early as 1876 it was recognized that C trionychids had unique cervical articulations - N N N N-_- (Vaillant, 1876) and the cervical series con- 4- tinues to be used as strong evidence for o of the coZ rn monophyly Trionychidae (Boulenger, C-.o; 1 1889; Siebenrock, 1902; Loveridge and Wil- enN and for 0 liams, 1957) monophyly ofthe Trion- 0% : * N N N 3N - - - N - 4) (A I ychidae plus Carettochelyidae (Meylan, 14) C) 0% 1 1985). In both families all cervicals are opis- 1 .CU CUV. thocoelous (character 83, table for CU '0 18) except CU 4) the eighth in trionychids, which has no cen- c)0H tral contact to the first thoracic vertebra 4) N -______N - N (character 84, table 18). All other cryptodires have at least one Cu, biconvex vertebra (number or some en 4) 2, 3, 4), procoelous vertebrae, and LU contact 0 4.. . between the centrum of o -4I - _" _. -_ _ the first tho- 0% _ -_ -_ CU racic vertebra and the centrum of the eighth e-CU .4 cervical (Williams, 1950). 00O0 N NM MMe-} N - - - - - U 4) The members of the Trionychidae are also CU in no CUo 00 I N N S N _. _. _4 _-- _. _ I unique having ventral process on the 4)4- eighth cervical (fig. 1 9B). A single or double is . on 00 N _" _" _. _m _ _ -__ _ _ C) process present the eighth cervical of CU all other cryptodires 1 character C't CU (fig. 9A, C, D; 00 c .C table e) 85, 18). Its absence in this family can 'C be correlated with CA en c '0 the unique 4. 00 CU neck-packing I.. CU mechanism described U, by Dalrymple (1979). c I- The double ventral process of the eighth cer- 4) vical, which is found only in kinosternids and 00 c 00 .CU Carettochelys (fig. 19C, is considered to C) D), cN _ .- be _" _. -_ _ _" _ _ _. _ a4 derived but lost in 00 0: trionychids (character AU 86, table 18). 0%- -_ e N N N - N N N 0 The only relief on the ventral surface of the eighth cervical of trionychids is a small terior keel pos- 4) found in a few large species acter (char- 4- 87, table 17). Such keels are absent in other trionychoids and are CZ CUn E W ES Y E'aY considered to be CZ 4)! derived within the family. 4) Like other cryptodires, most trionychids lack dorsal processes of the cervicals. How- ever, four species have very well developed 1987 MEYLAN: TRIONYCHIDAE 49

A B

Fig. 18. Dorsal views of the hyoids of six eucryptodiran turtles. A. Mauremys caspica (after Sieben- rock, 1913); B. Lissemyspunctata (after Annandale, 1912); C. Trionyx hurum (modified from Annandale, 1912); D. Chitra indica (BMNH 1984.1276); E. T. gangeticus (after Annandale, 1912); F. T. euphraticus (after Siebenrock, 1913). Stippled areas represent unossified cartilage. dorsal processes on the middle to posterior these processes is considered derived (char- cervical vertebrae (fig. 20). The presence of acter 88, table 17). 50 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 186

A B C D

1k~ >. ( /10

Fig. 19. Ventral view of the eighth cervical vertebra of four eucryptodiran turtles. A. Trachemys scripta (AMNH 111961); B. Trionyxferox (AMNH 129737); C. Staurotypus triporcatus (83-JI-202); D. Carettochelys insculpta (UF 43823).

Chelonians have 10 thoracic vertebrae be- ninth thoracic vertebra is like the tenth in tween the cervicals and the sacrals, and they having no contact between the transverse normally have 8 pairs ofpleural bones. Thus, processes and the carapace. In this family two thoracic vertebrae are not associated with both the ninth and tenth vertebrae exhibit a pair of pleurals. One of these is the first some freedom of movement. body vertebra. It sends transverse processes The distribution among all turtles of these posterolaterally to join the anterior edge of three conditions ofthe posterior thoracic ver- the ribs associated with the first pair of pleu- tebrae (character 89, table 18), suggests that rals (fig. 6). The other vertebra which is with- reduced articulation between the shell and out associated pleurals is the tenth. The tenth these posterior vertebrae is derived. thoracic vertebra may be firmly fixed by transverse processes which brace it against a tuberosity on the eighth pleural (fig. 6A), or it may be somewhat less well fixed and have PELVIS only remnants of transverse processes (fig. Numerous features ofthe trionychid pelvic 6B, C; Zug, 1971). In the Kinosternidae the girdle are useful in phylogenetic analysis. There are no fewer than 10 characters which are germane to establishing interfamilial relationships. Three of these are used in the A intrafamilial analysis as well. The pelvic girdle is treated as follows: ilium first, and then puboischiatic plate from anterior to poste- nor. The ilia in most turtles extend dorsally from the acetabulum to meet the carapace and transverse processes of the sacral vertebrae. The main axis of the ilium is straight in all turtles except trionychids (Zug, 1971). In B trionychids they are strongly flexed posteriorly (character 101, table 18). Zug (197 1) indicated that these posteriorly curved ilia do not articulate with the carapace in trionychids. This is certainly the case in all trion- Fig. 20. Lateral views ofthe sixth cervical ver- ychine trionychids, but carapacial contact tebrae of two trionychid turtles. A. Cycloderma does occur in some cyclanorbines (see dis- aubryi (MRAC 19212); B. Trionyxferox (AMNH cussion of shell character 21). 129737). Anterior is to the right. Hirayama (1985) has suggested that lateral 1 987 MEYLAN: TRIONYCHIDAE 51 curvature of the ilia is a feature unique to the a derived and possibly paedomorphic feature Testudinoidea. I believe he means medial (character 105, table 18). curvature because I find medially curved ilia The pectineal processes extend from the in all testudinoids examined. In numerous body of the pubis in an anterior or antero- trionychoids including some trionychids lateral direction. In most cryptodires they are (character 100, table 17), Carettochelys, small relative to the length of interpubic con- Dermatemys, and most kinosternids (charac- tacts (fig. 21A, B, D). The members of the ter 100, table 18) the ilia are also medially Trionychidae are unique in having pectineal curved. The character state is therefore shared processes which are as wide as or wider than by all ofGaffney's (1984) Chelomacryptodira the length of interpubic contact (fig. 21 C, E, (Trionychoidea plus Testudinoidea). Its ab- F; character 108, table 18). sence in most trionychids can be considered The pectineal processes and the interpubic a loss ofthe condition, and thus derived with- symphysis of trionychids lie in a single plane in the family. and they all lie flat against the plastron (Zug, The dorsal end of the ilium of all turtles 1971). In nearly all other cryptodires no such except trionychids and smaller kinosternines common plane exists. The exceptions are liv- is anterioposteriorly expanded. This distal ing chelonioids and Claudius, but in these sagittal crest is the site where the transverse taxa the anterior pubic region does not lie flat processes of the sacral vertebrae articulate. on the plastron. In skeletons of very young Based on a single individual, Zug (1971) de- specimens of Kinosternon and Sternotherus scribed the distal end of the ilium of Derm- the entire pubis is quite flat. It appears that atemys as being unexpanded. In four Derm- the pelvis first ossifies in a single plane and atemys and in three Carettochelys (not with age gains three-dimensional qualities. examined by Zug) available for this study the Thus the occurrence of a flat pubis in trion- distal ilia are anteroposteriorly expanded. The ychids may be a retention ofthe juvenile state absence of this distal expansion is considered (charactor 106, table 18). derived (character 102, table 18). The thyroid fenestra is the major opening The thelial process, site of attachment for in the puboischiatic plate. In turtles it is often the iliotibialis muscle, has been considered partially or completely divided by bone (fig. to be a unique feature of the Kinosternidae 21A). Bony division occurs in two nonho- (Zug, 197 1). A topographically and morpho- mologous ways: by ossification ofthe median logically similar structure occurs on the ilium gastroid cartilage or by junction of medial of all three Carettochelys pelves available to extensions of the pubes and ischia (Walker, me (fig. 21 B, D). In addition, a small tubercle, 1973). in the position of the thelial process, is pres- A divided thyroid fenestra is the common ent in three of six individuals of Lissemys condition among Recent turtles (character punctata examined (fig. 21E). The presence 104, table 18; Baur, 1891a; Zug, 1971). But ofa thelial process is considered to be derived the bony junction in chelydrids and Derm- for kinostemids and Carettochelys (character atemys occurs through ossification of the 103, table 18). medial gastroid cartilage, a structure which The epipubis is a small plate of cartilage is found in all open forms (Baur, 189 la). This or bone which extends anteriorly in a hori- is a minor modification of an otherwise com- zontal plane from the region of the pubic pletely open condition. Very distinct reduc- symphysis (fig. 21A, B). Hay (1908) has sug- tion and division of the thyroid fenestra oc- gested that an unossified epipubis is primitive curs by extention of the pubis and ischium for turtles. Although it is the last center in into the fenestra. Among living cryptodires the pelvic girdle to ossify it does ossify in all this occurs only in Platysternon, kinosternine cryptodires except the most derived triony- kinostemids, and testudinoids. choids (the Carettochelyidae and Trionychi- Baur's (189 1a) interpretation of this char- dae, fig. 21 C-F), most cheloniids (Baur, acter is that an open thyroid fenestra is prim- 189 la, reports that some old cheloniids os- itive and a divided fenestra derived. Data sify the epipubis), and testudinids. The lack from living turtles support this hypothesis. of ossification of the epipubis appears to be However, Proganochelys (Gaffhey, MS), some VOL. 186 52 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY

isch

metischial process

Fig. 21. Dorsal views of the pelvis of six eucryptodiran turtles. A. Pseudemys nelsoni (AMNH 129736); B. Staurotypus triporcatus (UF 13482); C. Trionyxferox (AMNH 129737); D. Carettochelys insculpta (AMNH 84212); E. Lissemys punctata (UF 56017); F. Chitra indica (FMNH 224228). Ab- breviations: il, ilium; isch, ischium; pub, pubis. Stippled areas represent calcified cartilage. 1987 MEYLAN: TRIONYCHIDAE 53 chelonioids, and some baenids (Hay, 1908) PEcroRAL GIRDLE have the thyroid fenestra divided by ischial- The pectoral girdle of all turtles is a trira- pubic contact. If the divided condition is diate structure composed of two elements, found among other extinct families, the use the scapula and coracoid. From the acetab- of global parsimony may require this state to ulum the main body of the scapula extends be recognized as primitive. Should this be the dorsomedially to the carapace in the region case, then an open foramen could be used as ofthe first body vertebra. The acromion pro- a shared derived character within the Che- cess of the scapula extends anteromedially to lydridae, the Chelonioidea, and Trionychoi- the plastron. The coracoid joins the scapula dea. For the present, Baur's interpretation is only at the glenoid fossa and projects pos- accepted. teromedially toward the midline of the plas- Baur (1 8 9 1 a) indicated that expansion of tron. The relative lengths of these three pro- the undivided thyroid fenestra in trionychids jections and the angles between them vary in is a uniquely derived condition. This fenestra a systematically useful manner. Their use in is open widely, and ischial extension into it systematics up to this time appears to be lim- is minimal (Dermatemys and staurotypines, ited (Meylan and Auffenberg, 1986). fig. 21 B) or absent (most trionychids and Ca- In most turtles, the dorsal projection ofthe rettochelys, fig. 21 D-F) in all trionychoids ex- scapula is the longest of the three pectoral cept for kinosternines. When the ischia do processes. The only exceptions are the chel- extend into the thyroid fenestra in species of onioids, trionychine trionychids, and Ca- the Trionychidae (fig. 21E), this is considered rettochelys in which the coracoid is longer to occur by reversal to the primitive condi- (character 113, tables 17, 18). The shortest tion. It appears only in Lissemys punctata, projection is the acromion process of the Cycloderma aubryi, and C. frenatum (char- scapula except in the Testudinoidea in which acter 107, table 17). the always shortest (character 1 1 1, Most trionychids, and in fact most cryp- coracoid is todires, have distinct, posteriorly directed table 17). An exceptionally long or excep- processes of the ischia, the metischial pro- tionally short coracoid is considered to be cesses (fig. 2 1A, D, F). In seven species of derived. trionychids (all five living species of the Cyc- Two angles in the pectoral girdle, one be- lanorbinae, Trionyx euphraticus, and T. fe- tween the acromion process and main body rox) these processes exist only as posteri- ofthe scapula and the other between the acro- omedial of the ischia and not as mion process and the coracoid, were mea- expansions sured. In most cryptodires the former angle free projections (fig. 21 C, E). Outgroup taxa approaches 90° and is always much greater which also lack metischial processes include than the latter. The same is true for majority Claudius, Staurotypus (fig. 21B), some Kin- oftrionychids although the larger angle tends osternon, some Dermatemys, and some In six taxa the cheloniids. Because metischial processes are to be somewhat less (65-75°). in arcomion-scapula angle is lower still and the present Carettochelys (the proposed sister coracoid-acromion angle is higher, so that group for the Trionychidae), some members there is little or no difference between them. ofthe other two trionychoid families and most The similarity of these two angles is consid- other turtles, their presence is judged to be ered to be a derived character state within primitive for the Trionychidae and their ab- table sence derived (character 109, tables 17, 18). the Trionychidae (character 112, 17). One additional character of the pelvis, which bears on the current problem only in APPENDICULAR SKELETON that it supports monophyly of the Kinoster- The humerus and femur of trionychids are nidae, is a distinct notch in the acetabulum remarkably similar in general appearance. at the junction of the ilium and ischium (fig. Both form gentle S-shaped curves, both have 21B). Such a notch is present in Staurotypus, two large proximal trochanters which are free Claudius, and most Kinosternon (character from each other, and both have weakly dif- 110, table 18). ferentiated distal tubercles. The humerus can 54 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 186

be distinguished from the femur most easily number of phalanges in digits one, two, and by the presence of an entepicondylar groove three (those which are clawed) but a variable that is always open in this family. Further- number in digits four and five. The most more the lesser trochanter ofthe humerus lies common phalangeal formula for turtles is 2-3- in an anteroposterior plane that runs through 3-3-3 (Romer, 1956). In those digits of trion- the main axis of the humerus. The greater ychids which are clawed, 1, 2, and 3 have this trochanter of the humerus and both trochan- number. Those which have no claws (digits ters of the femur lie at a high angle to this 4 and 5) may differ from this most common, plane. and according to Hay (1908), primitive num- The condition of the entepicondylar fora- ber. In almost every trionychid for which an men of the humerus is constant in the Tri- articulated manus is available the fourth digit onychidae, but it can be open or closed in has at least four phalanges, a few have five, pleurodires, Kinosternon, Dermatemys, and and Lissemys and Chitra have as many as among the various genera ofemydids. It clos- six. Only Cyclanorbis senegalensis (one spec- es with age in chelydrids, and is apparently imen available) appears to retain the primi- always closed in Carettochelys. It is always tive number of three elements. Despite this open in cheloniids and staurotypines. Be- exception, hyperphalangy of the fourth digit cause the closed condition is found in some is considered to be a derived feature of the members of all three outgroup trionychoid Trionychidae. Hyperphalangy ofthe fifth dig- families, the consistently open condition in it of the manus is less common in the Trion- the Trionychidae is unique within the super- ychidae. Although there is some interspecific family (character 79, table 18). variation within the data set for both ofthese The carpus and tarsus of trionychids do characters, the data are not sufficient to allow not differ significantly from those of other use of this character in the intrafamilial anal- cryptodires (Hay, 1908; Ogushi, 191 1). The ysis. carpus consists of ten elements: an interme- Hyperphalangy of the fourth digit of the dium, ulnare, and pisiform, two centralia, and pes is also commonplace for trionychids. five carpals. Unlike most other turtles, the There is variation among family members trionychids do not have the intermedium but, like the manus, the data are insufficient separating the distal ends of the radius and to include them in the analysis of intrafa- ulna; instead these forearm elements have a milial relationships. Hyperphalangy is treat- strong contact. The only other taxa in which ed as a single character (character 80, table this occurs are the families Cheloniidae and 18) and is used only in the interfamilial anal- Testudinidae (character 81, table 18). yses. Among trionychids there is a uniform

DISCUSSION HIGHER RELATIONSHIPS OF nychidae to the Kinosternidae and Derma- THE TRIONYCHIDAE temydidae was first proposed late in the last MONOPHYLY OF THE TRIONYCHOIDEA century by Baur (1891 a). Although it has subsequently been supported by the work of Al- The characters examined during the course brecht (1967), Zug (1966, 1972), and Gaffney of this study support the hypothesis that the (1975, 1979b, 1984), it is not frequently cited families Dermatemydidae, Kinostemidae, (an exception is Smith and Smith, 1980). An Carettochelyidae, and Trionychidae form a alternative proposal for the higher relation- monophyletic group. These relationships were ships of turtles by Williams (1950, repro- suggested by Gaffhiey (1975) who assembled duced here as fig. 23) has received wider use these families as the superfamily Triony- (Dowling and Duellman, 1974; Goin and choidea (fig. 22). Relationship of the Trio- Goin, 1962, 1971; Porter, 1972; Pritchard, 1987 MEYLAN: TRIONYCHIDAE 55

TABLE 19 Shared Derived Osteological Characters of the Trionychoidea Char- acter code Derived state 26 at least one pair of plastral buttresses fails to reach pleurals 39 cheek emargination reduced 43 palatines contribute significantly to braincase 55 basis tuberculi basalis absent 57 canalis carotici straight and wide 61 no groove for stapedial artery on prootic or parietal 77 quadrate contribution to processus trochlearis oticum less than 50% 94 surangular always present in area articularis mandibularis 89 transverse processes of tenth body vertebra do not articulate with carapace Fig. 22. A cladogram of living turtle families based on Gaffney (1984) with recognition of the Bataguridae from Hirayama (1985). Character states indicating monophyly ofthe Trionychoidea carettochelyids had been thought of alter- are enumerated in figure 24. natively as pleurodires (Boulenger, 1889), as the missing link between trionychids and chelonioids (Strauch, 1890), or as a link be- 1979a, 1979b; Romer, 1956, 1966; Wermuth tween dermatemydids and kinosternids, and and Mertens, 1961; Zug, 1966). The Williams the Trionychidae (Baur, 1891a; Gaffney, arrangement places the family Trionychidae 1975; and others). It is abundantly clear from alone in the superfamily Trionychoidea. The the present analysis that the last ofthese three Kinosternidae (as the Kinosterninae and alternatives is the one best supported by Staurotypinae) is included in the Chelydridae available data. which, along with the Dermatemydidae, is Although the present study has not reex- considered part ofthe Testudinoidea (fig. 23). amined characters of the cranial arteries The Carettochelyidae is confined to its own (McDowell, 1961; Albrecht, 1967; and Gaff- superfamily, the Carettochelyoidea. ney, 1975, 1979b, 1984), two of the external Gaffney (1984) summarized the evidence skull characters examined do reflect the dif- for using the superfamily Trionychoidea ferent arterial patterns that distinguish trion- (sensu Gaffney, 1975) which until now con- ychoids from other cryptodires. The small sisted largely of characters of the cranial ar- size of the stapedial artery in trionychoids is teries. Additional characters ofthe skull, low- reflected by the absence of any grooves or er jaw, shell, and body vertebrae are here furrows to accommodate this vessel where it shown to support this inclusive view of the crosses the prootic and the descending pro- Trionychoidea (table 19) as the most parsi- cess of the parietal (character 61). In chely- monious hypothesis for relationships among drids, emydids, and testudinids, by contrast, living eucryptodires. Furthermore, the cri- there is a distinct though variably developed teria which Williams (1950) used to include furrow or groove for the stapedial artery. In the Kinosternidae in the Testudinoidea are certain taxa (Chelydra, Melanochelys, Ter- shown to be plesiomorphic or subject to ho- rapene) these grooves extend for long dis- moplasy. tances. In other forms, especially testudinids, A critical feature of Gaffihey's (1975, 1984) they are short but deep and found only ad- definition of the Trionychoidea is the inclu- jacent to the foramen stapediotemporale. sion of the Carettochelyidae. Previously, the The second arterial feature noted here re- 56 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 186

LU 44 LU Z t LU 4Lu~ ~~~~~~~~LU4 z L *4L z LUo z Lu z w4 cc z z i z z ui ~zz~~~~~~lz LU LU j 0w 0 0~~ ~ ~ ~ ~ ~ 0 ~~~~~~~~~~~z ch 02 zL Z 4J23. Ao. LU I,L t LU ,L L -J LU~ ~~2 ~~~4 0 ~ L 4 LU 4 ' L a U z LU ~~~~~~~~ -.'~~~~ LU zU 2 4 _ 0 o ot IC z 0x~~~~~~~~~~~~~ I.-. W~~Zu~~a-o ~~~o a 0 ' ~~~~~~~~00 LU z -J ~~ I- ~~ -I I- 4 LU~~~~~~~Z 0 cc ~~~~~~~LU L

a ~~~~~~~~~4c 2 44 LU0 L -LIU a LU a CZ 5 - a S

I-

Fig. 23. A cladogram of the Testudines based on the classification in Williams (1950).

flects the increased importance ofthe internal (character 43) (Morenia and Hardella have a carotid artery in Recent trionychoid skulls. strong palatine contribution to the braincase In this superfamily, a stiff wire of a diameter wall, McDowell, personal commun.). In just less than the foramen posterior canalis trionychoids it is quite extensive, often ex- carotici interni, will pass easily from this fo- tending posteriorly nearly to the foramen ner- ramen through the foramen anterior canalis vi trigemini (fig. 13). carotici interni, and into the braincase (char- There are three additional features of the acter 57). This is possible because the canalis trionychoid skull which can be added to the carotici follows a very straight path. In other evidence for monophyly. The cheek is solid living cryptodires the path followed by the (little cheek emargination, character 39); the internal carotid artery is less direct as can be dorsal surface of the basioccipital is smooth seen in figures 26-29 in Gaffney (1979b). (no basis tuberculi basalis, character 5 5); and A useful feature of the skull used by Gaff- less than one-third of the processus trochle- ney (1975), which does not involve blood aris oticum is made up by the quadrate (char- flow pattern is the inclusion of the palatine acter 77). in the lateral wall of the braincase. In essen- Among living turtles only living chelo- tially all turtles other than trionychoids, pal- nioids (Cheloniidae, Dermochelyidae) and atine participation is insignificant or absent Platysternon share with the trionychoids such 1987 MEYLAN: TRIONYCHIDAE 57

limited cheek emargination. In none of these curs also in Recent chelonioids, testudinoids, taxa does it extend above the lower rim of and Platysternon (character 89). In Chelydra the orbit. Well-developed cheek emargina- and Macroclemys this contact is variable. If tion in the Pleurodira, baenids, pleisoche- the presence of free transverse processes of lyids, and most chelydrids suggests that its the tenth body vertebra is actually primitive, absence in the Chelonioidea and Triony- then this character would be equivalent to choidea is derived. the alternative possibility given for the plas- The basioccipital is without a basis tubercli tral buttresses above. That is, complete tenth basalis in certain cryptodires and may be most transverse processes would be derived for the easily explained as a single loss in the Trion- Chelonioidea and Testudinoidea and this ychoidea and a single loss in the advanced would exclude any trionychoids from either Testudinoidea (Rhinoclemmys and the Tes- of these superfamilies. tudinidae, except Gopherus). The small In summary, there are seven osteological quadrate contribution to the processus troch- characters, in addition to the two that cor- leans oticum also occurs in two separate relate with cranial circulation patterns, that monophyletic groups, the chelonioids and the suggest that the Trionychoidea (sensu Gaff- trionychoids. ney, 1975) is monophyletic. The most com- A single character of the lower jaw lends monly cited alternative, which places the support to the argument for monophyly of Dermatemydidae and Kinostemidae along the Trionychoidea. Throughout the super- with the Chelydridae in the Testudinoidea, family there is always contribution by the requires that all nine characters used here surangular to the area articularis mandibu- occur twice, once in the Trionychoidea and laris (character 94). In certain forms it makes once in the Testudinoidea. up the majority of this surface; in others it Observations on the morphology of the makes up a smaller part. It is never absent cloacal region support monophyly of the from this area, as in some testudinoids and Trionychoidea. In all four families cloacal chelydrids. bursae are absent (Smith and James, 1958). Absence of pleural contact by one or both This can be cited as additional evidence with plastral buttresses is a useful feature of the the assumption that absence in trionychids shell of trionychoids (character 26). The pres- occurs independently of absence in chelo- ence oftwo pairs ofwell-developed buttresses nioids and testudinids. Also, the penis in all in the Pleurodira, Plesiochelyidae, Baenidae, four families of the Trionychoidea has a sin- and testudinoids is used here as evidence that gly or doubly bifurcate seminal groove (Zug, they were present in primitive cryptodires 1966), a condition that occurs elsewhere only and that absence of one or both pleural con- in the Testudinidae. tacts can be considered derived for chely- The evidence presented by Williams (1950) drids, chelonioids, and trionychoids. Even if for including the Kinosternidae (as the Kin- absence of plastral buttresses were the prim- osterninae and Staurotypinae) within the itive condition for cryptodires, the character Chelydridae consists of two plesiomorphic is still a very useful one. Testudinoids could characters, and three highly variable char- then be recognized as having two pairs of acters. The existence of costiform processes well-developed plastral buttresses except for of the nuchal is widespread among crypto- the most kinetic forms (Cuora, Terrapene). dires and is most clearly visible in hatchlings No trionychoid taxa could be included in such and juveniles. Their retention in adults could a group. be considered a shared derived character of An important character of the posterior the chelydrids and kinosternids but they are thoracic vertebrae is used here as evidence also retained in adult Dermochelys, Derma- of monophyly ofthe Trionychoidea. As men- temys, and trionychids. Their presence is tioned by Zug (1971), the tenth body verte- probably primitive for the Cryptodira. bra, which is immediately anterior to the sa- The evidence from the cervical formula is cral pair, lacks contact of its transverse similarly of little value. The presence of a processes to the pleurals in members of this single biconvex vertebra and a doubly pro- superfamily (fig. 6B, C). This condition oc- coelous eighth cervical is used by Williams 58 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 186

(1950) as evidence of relationship of chely- results are in irreconcilable conflict with the drids and kinosternids. But these features are morphological evidence. Their observation also present in chelonioids and dermatemy- that the Trionychoidea and Carettochelyidae dids which suggests that they are actually have been separated from the Dermatemy- primitive for eucryptodires. Independent didae and Kinosternidae "for a long period modification of this cervical formula sup- of time" has no bearing on the cladistic reports monophyly of the Testudinoidea (usu- lationships of these families. ally two biconvex cervicals in the cervical The data examined in the current study series) and the Carettochelyidae plus Trio- support alliance of the Kinosterninae and nychidae (no biconvex cervicals, numbers two Staurotypinae with the other trionychoids as through seven opisthocoelous). suggested by Baur (189 la) and advocated by Williams (1950) cited a variable number Gaffhey and others. Additional characters of marginal scales, 23 or 25, as a character which indirectly indicate monophyly of the of his Chelydridae. The number of marginal Trionychoidea (sensu Gaffney) are shared by scales reflects variation in the number of pe- members of the Kinosternidae, Carettoche- ripheral bones (Hutchison and Bramble, lyidae, and Trionychidae. But these charac- 1981). The Williams arrangement would re- ters suggest an alternative to the dichotomous quire that reduction in the number of pe- view of the Trionychoidea used in Gaffiney ripheral bones from 22 to 20 occur twice, (1975, 1984) and shown in figure 24A. once in his Testudinoidea and once in his Carettochelyoidea. In the arrangement ad- MONOPHYLY OF THE KINOSTERNIDAE, vocated here this can be treated as a single CARETTOCHELYIDAE, AND TRIONYCHIDAE event and as part of a transformation series which culminates in complete loss of periph- Gaffney (1984) viewed the Trionychoidea erals in the Trionychidae. as two clades, one the Dermatemydidae and Broad unridged alveolar surfaces occur in Kinosternidae, and the other the Trionychi- numerous unrelated taxa in addition to those dae and Carettochelyidae (figs. 22, 24A). included in Williams' Chelydridae. They ap- Hutchison and Bramble (1981, fig. 4) detailed parently correlate with a durophagous diet the relationships within the dermatemydid- (Pritchard, 1984) and do not constitute strong kinosternid clade. They cited Albrecht (1967), evidence ofcommon ancestry ofkinostemids Gaffney (1975), McDowell (1961), Zug and chelydrids. The cruciform plastron is a (1966), and Frair (1964) for evidence of the similarly variable character being absent monophyly of these two families. They did within Williams' Chelydridae (many Kino- not subscribe to the idea that the Derma- sternon species) and present outside of this temydidae and Kinosternidae share a unique family (certain trionychine trionychids and common ancestor with the Trionychidae and extinct carettochelyids). There is no strong Carettochelyidae. They believed that the evi- case for including the Kinosternidae within dence cited by Gaffney (1975, 1984), simi- the Chelydridae on osteological grounds. larity in blood flow patterns, is convergent. Bickham and Carr (1983) suggested that As evidence they cited the presence of a large the staurotypines are the sister group of the foramen stapediotemporale in Adocus, which Testudinoidea (in which they include Platy- they consider to be a primitive dermatemy- sternon), which supports the Williams ( 1950) did. A large foramen stapediotemporale ap- arrangement in part. These authors rely on pears in many trionychids but a large sta- the recognition of a homologous derived pedial artery does not (Albrecht, 1967, 1976; chromosome in the Staurotypinae, Emydi- Gaffney, 1979b). The occurrence of a large dae, and Testudinidae. The crux of their ar- foramen stapediotemporale in these taxa is gument is that the same microsome is fused due to the retention of the primitive condi- to the same identifiable acrocentric macro- tion. some in these three taxa. However, the com- The osteological characters examined in the bined microsome is euchromatic and ho- current study suggest an alternative to both mology of the short arm of their biarmed the Gaffniey (1975, 1984) and the Hutchison second group B macrosome seems tentative and Bramble (1981) arrangements (fig. 24B, at best (see King, 1985). It is clear that their C). Within the monophyletic Trionychoidea: w atine forms a significant part of the lateral wall of 'u a the braincase, - 55(2) basis tuberculi basalis ab- 4c 'U a sent (also absent in some batagurines and testu- 4c - e dinids), - 57(2) canalis carotici interni straight

z and wide, - 61(2) no groove for stapedial artery w ar present on parietal (also absent in some chelo- in z iI-- niids), - 77(2) quadrate makes up less than one- 4c z half of processus trochlearis oticum (occurs also 0 0 z 4: in chelonioids), - 89(2) transverse processes of a 7d U I.- tenth body vertebra do not reach pleurals (occurs in some chelydrids), - 94(2) surangular forms up to one-half of area articularis mandibularis. Node 2: - foramen stapediotemporale reduced or absent, - absence ofwave-form or pedicillate sculpturing of shell surface, - enlarged palatine artery A and foramen caroticum laterale. Node 3: - 5(2) total number of peripherals 20 or fewer, - 26(3) no plastral buttresses reach pleurals (occurs also in cheloniids and chelydrids), - 86(2) ventral pro- 'U cess on eighth cervical double (lost in trionychids 4 Ul a which have no ventral process on eighth cervical), 4 - 89(3) transverse processes of body vertebrae 9 : I- o' -i Lu and 10 do not reach pleurals (reversed in Caret- a 'U 4 tochelyidae and Trionychidae in which only tenth z 7: fails to reach pleurals), - 97(2) foramen nervi 0

I- auriculotemporalis with one lateral and one dorsal I- z opening (reversed in Carettochelyidae and Tri- 0 cc 0 z onychidae), - 103(2) thelial process present, - 4C i-c 110(2) ilioischial notch present (lost in Caretto- a chelyidae and Trionychidae). Node 4: - 47(2) foramen intermaxillaris present, - 107(2) ischia do not extend into thyroid fenestra of pelvic girdle. Node 5: Characters unique to the Carettochelyidae and Trionychidae: - 28(2) ribheads strongly sutured to vertebral centra, - 30(2) shell sculptured B and lacking epidermal scutes, - 44(2) premaxillae fused, - 46(2) basisphenoid contacts palatines, - UJ 50(3) vomer never in contact with pterygoids, - 4 LuI 56(2) foramen posterius canalis carotici interni a 4 completely surrounded by pterygoid, - 83(2) cer- a0 - 4: ul vicals 2 through 7 - z ophisthocoelus, 94(3) 50 per- a z 'U 4 a cent or more of area articularis mandibularis is C) formed by surangular, - 99(2) retroarticular pro- I~- 0 cess forms about one-tenth of mandible length. LI- I- I- 0 4c I- 7 Characters of the Carettochelyidae and Trionych- 0 idae which also appear in some or all che- z 4c living IC'U ;- 1-- 4c lonioids: - 6(2) peripherals never sutured to pleurals, - 52(2) processus pterygoideus externus does not project laterally, - 81(2) radius and ulna in contact adjacent to manus, - 82(2) clawed digits of manus three or fewer, - 105(2) epipubic region '4 never ossifies, - 113(2) coracoid longest of three r- pectoral processes. Characters of the Carettoche- f, 1 _O lyidae and Trionychidae also found in testudinids and some chelydrids: - 37(2) incisura columella Fig. 24. Three alternative cladograms for the auris closed. Characters of Carettochelyidae and Trionychoidea. The distribution of character states Trionychidae which must be reversals in clado- for the numbered nodes is as follows: Node 1: - gram presented in figure 24C: -89(2) only the 26(2) one pair of plastral buttresses reaching pleu- tenth body vertebra with transverse processes rals, - 39(2) cheek emargination does not extend which do not reach the pleurals, - 97(1) foramen above ventral edge of orbit (occurs also in chelo- nervi auriculotemporalis with both openings lat- niids, Platysternon, and Malayemys), - 43(2) pal- eral, - 110(1) ilio-ischial notch lost. 60 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 186

(1) the Trionychidae and Carettochelyidae mydidae and Kinosternidae. Megacephaly is share a unique common ancestor; (2) the as well developed in some trionychids (Tri- Staurotypinae, Carettochelyidae, and Tri- onyx cartilagineus and especially T. subpla- onychidae share a common ancestor not nus) as it is in megacephalous kinostemids shared by the Kinosterninae and Derma- (Claudius angustatus, Sternotherus minor). temydidae (fig. 24C); and (3) the Derma- The tricarinate carapace is certainly absent temydidae is the sister group to all other fam- in some dermatemydids and in some kino- ilies of the Trionychoidea. sternines. The reduction ofcarapacial keeling This arrangement is supported by 28 char- could very likely be a result of the flattening acters from the present study, 17 of which of the shell which occurs in the clade leading suggest monophyly of the Trionychidae plus to trionychids. Carettochelyidae (table 20). These characters The one remaining nonscute character can be integrated with those used by Gaffiey which Hutchison and Bramble (1981) con- (1984) and Hutchison and Bramble (1981) to sidered to be evidence of monophyly of the support the arrangement shown in figure 24C Kinosternidae plus Dermatemydidae, exclu- as the most parsimonious for the Triony- sive of the Trionychidae and Carettochelyi- choidea. dae, is the loss of sculpturing of the shell. Monophyly of the Kinosternidae, Caret- There would have to be reversal in this char- tochelyidae, and Trionychidae is suggested acter to allow the arrangement advocated by two characters of the shell, one of the cer- here. vical series and one of the pelvis. In all mem- Two of the nonscute characters cited by bers of these three families there are 20 or Hutchison and Bramble (1981) for mono- fewer peripherals (character 5) and plastral phyly of the Kinosternidae are characters buttresses lack pleural contact (character 26). which I cite as evidence for the monophyly The ventral process of the eighth cervical is of the Kinostemidae, Trionychidae, and Ca- double (fig. 19) except in the trionychids in rettochelyidae. These are the possession of which this process is absent (character 86). 20 (or fewer) peripherals (character 5) and In the pelvis, a thelial process (fig. 21) is pres- the presence of a double ventral process of ent in kinosternids and Carettochelyids but the eighth cervical (character 86). is absent in nearly all trionychids (observed Other characters that these authors cite for only in specimens of Lissemys, MHNG the monophyly of the Kinostemidae do not 615.87, UMMZ 129396, UF 56017) (char- necessarily exclude the Trionychidae and acter 103). Carettochelyidae from this clade. These in- The inclusion ofthe Trionychidae and Ca- clude: the loss of neural eight, the tendency rettochelyidae in the same clade as the Kin- for development of a secondary palate, and osternidae in the Hutchison and Bramble development of impressed musk ducts in the (1981) arrangement requires that these taxa anterior peripherals. share the features shown to be derived for the Although most kinostemids have seven or dermatemydids plus kinostemids in that fewer neurals, both Staurotypus species have study. However, scutes are absent from all eight (numbers two through nine) on occa- trionychids and in carettochelyids only the sion (UF 58976, BMNH 1871.1.7.5). Other vertebral scutes develop and these are lost than lacking an independent first neural or soon after hatching (Zangerl, 1959); thus the preneural this is identical to the proposed many characters of scalation used by Hutchi- primitive number for trionychids. son and Bramble (1981) do not enter into the The development of a secondary palate is current argument. Many of the remaining not widespread enough among kinostemids characters of their dermatemydid-kinoster- to be a valid shared derived feature of this nid clade are shared by the Trionychidae and family. Hutchison and Bramble (1981) cited Carettochelyidae: posterior lobe reduced in Gaffiney (1979b) in support of this feature. width, stapedial artery reduced, large costi- Gaffiney mentioned the presence of a second- form processes, reduction of plastral bridge. ary palate only in two genera (Staurotypus Two other characters which they use, mega- and Xenochelys). The palate in the other gen- cephaly and the tricarinate carapace, are ac- era of this family are not remarkably elon- tually quite variable within the Dermate- gate. This character is ofvalue at a lower level 1 987 MEYLAN: TRIONYCHIDAE 61 ofuniversality (subfamily Staurotypinae) than opening comparable to the foramen inter- it is assigned in the Hutchison and Bramble maxillaris. arrangement. All four of the nonscute features used by Impressed musk ducts are clearly visible Hutchison and Bramble (1981) for evidence on the interior surface of the anterior periph- of monophyly ofthe Staurotypinae are shared erals (usually numbers two, three, and four) by the Trionychidae and Carettochelyidae. of all kinosternids. In Carettochelys, there is These are: (1) costal bone four spans periph- no duct impression but there is a canal through eral six (carettochelyids); (2) the anterior lobe the second peripheral. The interior opening is kinetic; (3) there are very short plastral of this canal is at the same level as the im- buttresses; and (4) scapular attachment is pressed duct in kinosternids, the exterior transferred from entoplastron to epiplastron. opening is identical in position to the anterior I find the second feature to be useful at a musk duct opening in trionychids. It is ap- higher level and I have used it as evidence parent that all trionychoids have anterior for monophyly of the Kinosternidae, Caret- musk ducts which exit just dorsal to the fore- tochelyidae, and Trionychidae. Attachment limbs. In kinosternids they leave an impres- of the scapulae to the epiplastra via the ac- sion in the anterior peripherals; in Caret- romial ligament has been verified for Ca- tochelys they leave no impression but rettochelys and the Trionychidae (Bramble apparently pass through the second periph- and Carr, MS). This feature may occur i eral. Trionychids have no anterior periph- kinosternines only because the entoplastron erals so the path of the musk duct cannot be is absent and thus it may not be homologous traced in osteological material. The condition to the condition in Staurotypines, Caret- in Carettochelys could be viewed as a mod- tochelys, and trionychids. ification of that seen in the kinostemids. The osteological data support an arrange- From the osteological evidence it appears ment of the families of the Trionychoidea that the best arrangement for the Triony- that has not been considered previously. That choidea is to regard the Dermatemydidae as is, monophyly of the Staurotypinae, Caret- a sister group to the other three families. Fur- tochelyidae, and Trionychidae (fig. 24C). That thermore, it is apparent that certain kino- the entire Kinostemidae might be the sister stemids have closer affinities to the caretto- group to the carettochelyid-trionychid clade chelyids and trionychids than others. (fig. 24B) is an alternative possibility. Monophyly ofthe Kinostermidae exclusive of the Trionychidae and Carettochelyidae is MONOPHYLY OF THE STAUROTYPINAE, suggested by four characters in addition to CARETTOCHELYIDAE, AND TRIONYCHIDAE those treated by Hutchison and Bramble One line ofevidence pursued in the present (1981). These are: (1) the presence of one study supports monophyly of the Staurotyp- dorsal and one lateral opening ofthe foramen inae, Carettochelyidae, and Trionychidae, and nervi auriculotemporalis (character 97); (2) evidence from Hutchison and Bramble (1981) two, rather than one, posterior thoracic ver- supports this view. The palate of all three tebrae having transverse processes that fail living species of staurotypines develops a fo- to reach the carapace (character 89); (3) the ramen intermaxillaris (character 47). It does presence of an ilioischial notch (Zug, 1971; not appear until maturity but it forms in ex- character l 10); and (4) the presence of clasp- actly the same manner as in carettochelyids ing or stridulating organs in most species. and trionychids. It lies between the vomer However, the most parsimonious arrange- and premaxillae with maxillae defining the ment of the osteological data results in the lateral edges. In staurotypines it allows the arrangement shown in figure 24C. symphyseal hook ofthe lowerjaw to pass into the nasal capsule. In other cryptodires with MONOPHYLY OF THE CARETTOCHELYIDAE re- well-developed symphyseal hooks, this AND TRIONYCHIDAE gion of the palate is usually deeply impressed (Chelydra, Macroclemys, Platysternon) or the Since it was first described, Carettochelys premaxillae may be slightly divided (Dei- has often been associated with the Trio- rochelys) but in no other turtles is there an nychidae (Baur, 1891b; Hummel, 1929; 62 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 186

TABLE 20 TABLE 21 Shared Derived Characters of the Trionychidae Uniquely Derived Features of the Trionychidae and Carettochelyidaea Char- Char- acter acter code Character state code Character state 5 18 or fewer peripherals; no pygal or supra- 6 peripherals never sutured to pleurals pygal 28 rib heads strongly sutured to vertebral centra 22 boomerang-shaped entoplastron 30 shell is sculptured and without epidermal 33 quadratojugal not in contact with postorbital scutes 35 jugal contacts parietal 44 premaxillae fused 45 premaxillae excluded from apertura narium 46 basisphenoid contacts palatines externum 50 vomer not in contact with pterygoids 80 hyperphylangy of manus digits 4 and 5, pes 56 foramen posterius canalis carotici interni digit 4 completely within pterygoid 82 three clawed digits in manus 94 50% or more of area articularis mandibularis 84 centra of eighth cervical and first body verte- formed by surangular bra not in contact 99 retroarticular process forms about one-tenth 85 no ventral processes on eighth cervical ofjaw 90 corpus hyoideum composed of six or eight 83 cervical centra 2-7 opisthocoelous ossifications 52 processus pterygoideus not projecting 101 ilia curve posteriorly 81 radius and ulna in contact adjacent to manus 106 pectineal processes in a single plane and in 82 number of clawed digits three or fewer broad contact with plastron 105 epipubic region never ossifies 108 pectineal processes equal to or wider than in- 113 coracoid longest of three pectoral processes terpubic contact 37 quadrate enclosing stapes 27 carapace not sutured to plastron a States for characters 6 through 83 are unique among are unique to these two families, trionychids the Cryptodira. States for characters 52 through 1 3 are and carettochelyids are also the only cryp- also found among the Chelonioidea. The state for 37 is todires known to have a fleshy proboscis. also found in the Testudinidae and Chelydridae; that for 27 is also found in both the Chelonioidea and Chelyd- MONOPHYLY OF THE TRIONYCHIDAE ridae. Monophyly ofthe family Trionychidae has, Ramsay, 1886; Siebenrock, 1909; Walther, to my knowledge, never been questioned. All 1922). It is clear from the characters consid- recent systematic studies treat the family as ered in the current study that this association a monophyletic unit (De Broin, 1977; Gaff- is very well supported by osteological data ney, 1975, 1979b, 1984; Bickham and Carr, (table 20). Ten of the features shared by these 1983; Meylan, 1985), but the osteological two families occur in no other cryptodire. evidence for monophyly has never been com- Five others are present in these two families piled. Therefore, the unique features of the and among the Chelonioidea. However, the family are listed in table 21. In combination many unique features of the Chelonioidea these synapomorphic features result in the (Gaffiney, 1975, 1984) and the Trionychoidea unique overall morphology ofthis distinctive discussed above suggest that these five char- family of turtles. acter states have been attained in parallel. Three of them are states of characters which RELATIONSHIPS AMONG THE may only reflect the modification of limbs RECENT TRIONYCHIDAE and girdles for a highly aquatic mode of life: Computer-assisted analyses of indepen- coracoid is longest of three pectoral process dent data sets from the skull, shell, and non- (character 1 13); reduction in number of claws shell postcrania reveal that there are numer- (character 82); and contact ofradius and ulna ous possibilities for explaining the character adjacent to the manus (character 81). In ad- state distributions of each data set by using dition to the 10 osteological characters that hypotheses of descent that require a mini- 1987 MEYLAN: TRIONYCHIDAE 63 mum number of evolutionary steps. By rec- parsimonious trees. This is due entirely to ognizing unresolvable areas in the multiple, alternative topologies of the unresolvable equal-length arrangements suggested by each portions of the trees. Two clades that appear data set, a single solution or consensus tree in all of the shortest-length trees cannot be for that data set was obtained. These fun- fully resolved by analysis of the data from damental cladograms vary between data sets the shell alone. These problematical clades in the degree of resolution of interfamilial are a group of Cyclanorbines (Cycloderma relationships, in their intemal consistency (the aubryi, Cycloderma frenatum, and Lissemys amount of parallelism and reversal required punctata) and the Indian species of the genus by the distribution of the character states), Trionyx. These two clades are shown to be and most importantly, in their topology. The unresolved in the tree which best represents relationships suggested by analysis ofthe skull the relationships of the Trionychidae based data (fig. 26) differ from those obtained by on shell morphology alone (fig. 25). analysis of shell data (fig. 25). The poor res- These results are generally compatible with olution achieved by the small nonshell post- those of Meylan (1985). The monophyly of cranial data set (fig. 27) limits the compara- the Trionychinae is supported. Monophyly bility of the topology resulting from its of the Indian species and its position as the analysis to that resulting from analysis of shell sister group to the remaining Trionychinae is or skull characters. also repeated. The Asian species occupy the Results of analyses of the three separate middle ground between the Indian clade and data sets (i.e., the fundamental cladograms, a previously recognized clade leading to the figs. 25-27) could not be resolved into a single North American forms. general cladogram following the methods of The most obvious divergences from the Adams (1972) or Nelson (1979). Therefore, previous arrangement (Meylan, 1985) are the these results are contrasted and compared to failure to recognize a monophyletic Cycla- one another and to six equally parsimonious norbinae and the recognition of most Asian trees (figs. 29, 30) based on an analysis of all species as a monophyletic group. In this re- three data sets combined. This comparison gard these results support the conclusions of suggests a choice of two alternative trees as De Broin (1977) who suggested that the Cyc- the best hypotheses for the relationships of lanorbinae may not be monophyletic and that soft-shelled turtles from osteological evi- the Trionychinae includes three monophy- dence (figs. 33, 34). letic groups, the Indian forms (her Aspider- ites), most other Asian forms (her Amyda), and a group which culminates in the North EVIDENCE FROM SHELL MORPHOLOGY American forms (her Platypeltis). A previous examination (Meylan, 1985) has The failure of analysis of the current shell indicated that there is sufficient variation in data to support a monophyletic Cyclanorbi- shell morphology among the shells of trion- nae, contrary to the findings in Meylan (1985), ychids to allow resolution ofthe relationships can be attributed to the inclusion of several of 20 of the 22 living species. The arrange- new characters not considered in that study. ment which resulted from that study is based Cyclanorbis elegans shares with the Tri- on 16 characters and the most parsimonious onychinae a reduction in length of the bony tree was produced by hand (fig. 28). That data bridge and articulation of the ilia against the set has been upgraded for the current study. cartilaginous part of the shell rather than on The present shell data matrix includes 40 per- the bony disc (characters 21 and 23). These cent more entries (21 characters x 22 taxa characters work in concert with reduced plas- vs. 16 characters x 20 taxa). With this in- tral callosities, a short nuchal bone, and the crease in data a search for the most parsi- united anterior and posterior costiform pro- monious tree proved to be too time consum- cesses (characters 1, 2, and 9) to suggest that ing by hand. A tree-producing package was the two Cyclanorbis species share a unique used to determine the most parsimonious ar- common ancester with the Tnionychinae. rangement ofthe Trionychidae based on shell However, the distribution of two characters data. This analysis produced a dozen equally which support monophyly of the Cyclanor- 64 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 186

Fig. 25. The most parsimonious cladogram of fused. Node 8: - 16(1) only eighth pleurals meet extant soft-shelled turtles based on 22 characters on midline (a reversal). Node 9: - 14(1) nine neu- of shell morphology. The characters defining each rals (fused one and two count two; a reversal). node are as follows: Node 1: - 1(2) nuchal more Node 10: - 17(2) point ofneural reversal at neural than two times wider than long, - 5(4) peripherals seven (a reversal). Node 11: - 20(3) anterior pro- absent, - 10(2) hyo- and hypoplastra fuse just cess of epiplastron long. Node 12: - 24(2) largest after hatching, - 13(2) posterior process of hy- adult size 200 mm or less (occurs also at node 17). poplastra lateral to anterior process of xiphiplas- Node 13: - 14(3) eight or fewer neurals (fused first tra, - 14(2) eight or nine neurals (after reversal and second count as two). Node 14: - 8(2) eighth to primitive condition at node 9, occurs again in pleurals reduced in size. Node 15: - 9(4) two plas- steindachneri), - 16(2) pleurals seven and eight tral callosities (occurs also in elegans). Node 16: or eight only meet on midline (after reversal at - 15(3) position ofneural reversal highly variable, node 8, occurs again in steindachneri), - 17(2) - 17(5) point of posteriormost neural reversal at point of neural reversal at neural seven, - 22(2) neural four, five, or six, - 29(2) sexual dimor- "boomerang-shaped" entoplastron. Node 2: - phism in disc size (occurs also in indica). Node 17: 19(2) epiplastra I-shaped, - 25(2) carapacial mar- - 9(1) up to seven callosities present in plastron gin straight or concave posteriorly. Node 3: - 1(3) (a reversal). Node 18: - 1(4) nuchal four or more nuchal bone three or more times wider than long, times wider than long (occurs also in subplanus), - 2(2) anterior and posterior costiform processes - 14(2) eight or nine neurals present (a reversal; united, - 3(2) anterior edge of first body vertebra fused one and two count two). Species characters: located at middle ofnuchal (occurs also in aubryi). punctata: - 5(3) 14 to 18 peripherals present, - Node 4: - 9(3) four or fewer plastral callosities 7(2) prenuchal bone present (occurs also in sene- (reverses twice), - 21(2) no depressions for the galensis), - 14(4) seven or eight neurals present. ilia on the eighth pleurals, - 23(2) bridge short. aubryi: - 3(2) anterior edge of first body vertebra Node 5: -10(1) hyo- and hypoplastra do not fuse at middle of nuchal (occurs also at node 3), - just after hatching (a reversal), - 13(1) anterior 17(1) neural reversal occurs at neural eight (a re- process of xiphiplastra lateral to posterior process versal which occurs also in elegans). senegalensis: ofhypoplastra (a reversal), - 17(3) point ofneural - 7(2) prenuchal bone present (occurs also in reversal at neural six or seven or anterior. Node punctata), - 9(0) nine or more callosities in the 6: - 9(2) five callosities present in plastron (a plastron, - 14(5) seven or fewer neurals, - 16(4) reversal that occurs also in cartilagineus), - 20(2) additional pleurals to six, seven and eight meet at anterior projection of epiplastron of intermediate midline. elegans: - 1(2) nuchal two times wider length. Node 7: - 4(2) first and second neurals than long (a reversal that also occurs in formosus 1987 MEYLAN: TRIONYCHIDAE 65

Fig. 25 (continued). the total number of neurals (character 14) and steindachneri), - 9(4) two plastral callosities although there is a reversal in this condition (occurs also at node 15), - 17(1) neural reversal in the most derived forms. occurs at neural eight (a reversal that occurs also in aubryi). indica: - 3(3) anterior edge offirst body vertebra occurs at anterior edge ofnuchal, - 29(2) sexual dimorphism in disc length (occurs also at EVIDENCE FROM SKULL MORPHOLOGY node 1 6).formosus: - 1(2) nuchal two times wider than long (a reversal that occurs also in elegans Like variation in the trionychid shell, vari- and steindachneri). cartilagineus: - 9(2) five cal- ation in the trionychid skull is sufficient to losities in plastron (a reversal that occurs also at allow nearly complete resolution of the re- node 6). steindachneri:- 1(2) nuchal two times lationships of all 22 living species. wider than long (a reversal that occurs also in ele- Analysis of 23 characters of the trionychid gans andformosus), - 14(2) eight or nine neurals skull using PAUP results in a minimum- (fused one and two count two), - 16(2) pleurals length tree of 99 evolutionary steps. Three seven and eight or eight only meet at midline (a equally parsimonious trees produced by rederived feature after reversal to the primitive PAUP differ only in minor changes in the condition at node 8). subplanus: - 1(4) nuchal of four times wider than long (occurs also at node positions Trionyxformosus and T. leithii. 18), - 15(2) point of neural reversal is always at Variation in the three trees is represented in adjacent neurals (also in hurum and gangeticus), the single solution cladogram by a trichoto- - 16(0) no pleurals meet on midline. sinensis: - my (fig. 26). The three equally parsimonious 8(1) eighth pleurals not reduced in size (a reversal), cladograms otherwise agree completely in the - 20(3) anterior process of epiplastra long, - remainder of their structure. 29(1) no sexual dimorphism (a reversal). The three arrangements all support a monophyletic Cyclanorbinae as the sister group to a monophyletic Trionychinae. Liss- binae (characters 10 and 13) in Meylan, 1985, emys punctata is always the sister group to are explained as unique reversals to the prim- all other cyclanorbines. Chitra indica and itive condition for all trionychines in figure Pelochelys bibroni form a clade which is the 25. Characters ofthe skull and nonshell post- sister group to the remaining Trionychinae. crania considered below and the results from Trionyx cartilagineus is the sister group to all three data sets analyzed together firmly two remaining major monophyletic units, the support monophyly ofthe Cyclanorbinae and North American group plus T. triunguis, T. the recognition of this subfamily. euphraticus, and T. swinhoei on the one hand, In the arrangement based on shell mor- and the Indian and Asian Trionyx species on phology, monophyly of the Indian species is the other. Unlike the arrangement based on supported by the occurrence of five plastral shell morphology, T. sinensis is placed among callosities in all species (character 9) (this oc- the Asian clade and T. subplanus is the sister curs elsewhere only in Trionyx cartilagineus) group to the North American clade. and on the occurrence of epiplastral projec- Although the arrangement based on skull tions of intermediate length (character 20). It data alone is initially more appealing for sev- is also possible that the existence of two neu- eral reasons, its internal consistency is lower rals between the first pleurals is a derived than that derived from shell data. The dis- feature arrived at independently in the Cycla- tribution ofnearly two-thirds ofthe character norbinae and the Indian forms. states in the skull cladogram must be ex- Monophyly of the Asian clade (Pelochelys plained by reversal or parallelism. The ap- bibroni through Trionyx subplanus) in figure pealing features of the skull arrangement in- 25 is supported only by an apparent reversal. clude its support of both subfamilies, the The eighth pleurals are the only pair that meet Cyclanorbinae and Trionychinae, as mono- on the midline, a condition which occurs phyletic units and its overall similarity to the elsewhere only in Trionyx leithii. Monophyly arrangement in Meylan (1985) which in turn of T. triunguis, T. euphraticus, T. swinhoei, approaches arrangements proposed by Love- the three North American forms, and T. si- ridge and Williams (1957) and De Broin nensis, is suggested by a unique reduction in (1977). Fig. 26. The distribution of character states in fuses to pterygoid in adults only (occurs also at the most parsimonious arrangement ofextant soft- node 6), - 76(2) quadratojugal participates inpro- shelled turtles based on 23 characters of skull mor- cessus trochlearis oticum (occurs also at node 8). phology. Evidence for the numbered nodes is as Node 6: - 70(0) when epipterygoid is present pter- follows: Node 1: - 33(2) quadratojugal never con- ygoid contacts foramen nervi trigemini between tacts postorbital, - 34(2) jugal contacts parietal epipterygoid and quadrate or not at all, - 71(2) on skull surface in one-half of sample (occurs in- epipterygoid contacts prootic anterior to foramen dependently in subplanus and muticus after re- nervi trigemini in one-half of sample (reverses at versal at node 8), - 35(2) jugal always contacts node 9), - 73(2) epipterygoid fuses to pterygoid - parietal within temporal fossa, - 45(2) premax- only in adults (occurs also at node 5). Node 7: illae always excluded from apertura narium ex- 34(3)jugal always contacts parietal on skull surface ternum, - 48(2) vomer never divides maxillae, (occurs also at node 3 and in formosus), - 48(1) - 53(2) foramen palatinum postenius small, - vomer divides maxillae (a reversal), - 68(3) epi- 60(2) foramen posterius canalis carotici interni pterygoid never contacts palatine (occurs also in within lateral crest ofbasioccipital tubercle, - 68(2) senegalensis and frenatum). Node 8: - 76(2) epipterygoid, when present, contacts palatine in quadratojugal participates in processus trochlearis one-half of sample. Node 2: - 54(2) foramen oticum (occurs also at node 5 and in formosus), palatinum posterius forms in palatine only (occurs, - 34(1) jugal never contacts parietal on skull sur- also in sinensis and swinhoei), - 58(2) foramen face (a unique reversal), - 41(2) dorsal edge of jugulare posterius excluded from fenestra postot- apertura narium extemum weakly laterally emar- ica by pterygoid arching dorsally to contact opis- ginate (occurs also at node 4), - 49(2) vomer nev- thotic, - 60(3) foramen posterius canalis ca- er reaches intermaxillary foramen (occurs also at rotici interni below lateral crest of basioccipital node 3), - 64(2) basisphenoid sometimes medi- tubercle (occurs also at node 9). Node 3: - 34(3) ally constricted (occurs also at node 20 after re- jugal always contacts parietal on skull surface (also versal at node 16). Node 9: - 60(3) foramen pos- occurs at node 7 and informosus), - 36(2) vomer terius canalis carotici interni below lateral crest of does not contact prefrontal (occurs also in indica, basioccipital tubercle (occurs also at node 2), - reverses in elegans), - 49(2) vomer never reaches 68(1) epipterygoid, when present, always in con- intermaxillary foramen (occurs also at node 8), - tact with palatine (a reversal that occurs also in 53(3) foramen palatinum posterius small and di- elegans), - 71(1) epipterygoid never contacts vided, - 69(2) no contact between pterygoid and prootic anterior to foramen nervi trigemini (a foramen nervi trigemini when epipterygoid is unique reversal). Node 10: - 64(3) basisphenoid - present (occurs also in muticus), - 72(2) epipter- always medially constricted, 70(1) when epi- ygoid contacts prootic posterior to foramen nervi pterygoid is present pterygoid contacts foramen trigemini. Node 4: - 41(2) dorsal edge ofapertura nervi trigemini between prootic and epipterygoid narium extemum weakly emarginate laterally (oc- or not at all (a presumed reversal). Node 11: - curs also at node 8). Node 5: - 73(2) epipterygoid 76(1) quadratojugal never participates in proces- Fig. 26 (continued). 73(3) epipterygoid never fuses to pterygoid (occurs sus trochleans oticum (a unique reversal), - 32(2) also at nodes 11 and 18 and in indica). hurum: - jugal contacts squamosal in one-half of sample 59(1) foramen jugulare posterius not excluded from (occurs also in muticus and swinhoei), - 73(3) fenestra postotica (a reversal). steindachneri: - epipterygoid never fuses to pterygoid (occurs also 34(3)jugal always contacts parietal on skull surface at node 18, in cartilagineus and in indica). Node (occurs also at nodes 3 and 7 and informosus), - 12: - 34(2) jugal contacts parietal on skull roof 71(3) epipterygoid always contacts prootic ante- in one-half of sample (occurs also at node 1, in rior to foramen nervi trigemini (occurs also in in- subplanus and in muticus). Node 13: - 41(3) dor- dica), - 75(2) postorbital bar very narrow, less sal edge ofapertura narium externum strongly lat- than one-fifth orbit width (occurs also in muticus, erally emarginate (occurs also at node 15), - 59(2) spiniferus, and subplanus). sinensis: - 54(2) fo- foramen jugularis posterius excluded from fenes- ramen palatinum posterius forms in palatine only tra postotica by descending process of opisthotic (occurs at node 2 and in swinhoei), - 70(2) when which reaches pterygoid (occurs also in subplanus, epipterygoid is present pterygoid contacts foramen absent in hurum). Node 14: - 31(1) quadratojugal nervi trigemini between epipterygoid and parietal contacts maxillary (a unique reversal), - 71(2) or not at all - 76(2) quadratojugal participates in epipterygoid contacts prootic anterior to foramen processus trochlearis oticum (occurs also at nodes nervi trigemini in 50% of sample (occurs also in 5 and 9). formosus: - 34(3) jugal always contacts cartilagineus, bibroni, and indica). Node 15: -41(3) parietal on skull surface (occurs at nodes 3 and 7 dorsal edge of apertura narium externum strongly and in steindachneri). leithii: - 70(0) when epi- laterally emarginate (occurs also at node 13). Node pterygoid is present, pterygoid contacts foramen 16: - 78(2) parietal makes up 22.1% or more of nervi trigemini between epipterygoid and quad- the processus trochlearis oticum (occurs also in rate or not at all (occurs also at node 6). nigricans: nigricans and elegans), - 64(1) basisphenoid not - 60(2) foramen posterius canalis carotici interni medially constricted in ventral view (a unique re- located in lateral crest ofbasioccipital tubercle (oc- versal). Node 17: - 48(2) vomer usually divides curs also in bibroni, cartilagineus, and indica), - maxillae (a unique reversal), - 74(2) intermax- 68(3) epipterygoid, when present, never contacts illary foramen extends across 60 percent of pri- palatine (occurs also at node 7 and in senegalen- mary palate. Node 18: - 49(1) vomer reaches in- sis), - 78(2) parietal makes up 22.1% or more of termaxillary foramen (a reversal that occurs also processus trochlearis oticum (occurs also at node in senegalensis), - 73(3) epipterygoid never fuses 16 and in elegans). subplanus: - 34(2) jugal con- to pterygoid (occurs also at node 11 and in carti- tacts parietal on skull surface in one-halfof sample lagineus and indica). Node 19: - 48(1) vomer (occurs also at node 12, in punctata and in muti- always divides maxillae (a reversal that also occurs cus), - 59(2) foramen juglare posterius excluded at node 7 and in senegalensis). Node 20: - 64(2) from fenestra postotica by descending process of basisphenoid constricted in some individuals (oc- opisthotic (occurs also at node 13), - 75(2) post- curs also in cartilagineus and subplanus). Species orbital bar less than one-fifth oforbit width (occurs characters. aubryi: - 53(4) foramen palatinum also in spiniferus, muticus, and sinensis). muticus: posterius divided into many small openings (oc- - 32(2) jugal contacts squamosal in one-half of curs also infrenatum), - 65(2) premaxilla absent sample (occurs also at node 11 and in swinhoet), in some individuals. senegalensis: - 48(1) vomer - 34(2) jugal contacts parietal on skull surface in always divides maxillae (occurs also at nodes 7 one-halfofsample (occurs also at node 12, in punc- and 19), - 49(1) vomer reaches intermaxillary tata and subplanus), - 69(2) contact between pter- foramen (occurs also at node 18), - 68(3) epi- ygoid and foramen nervi trigemini never occurs pterygoid, when present, never contacts palatine when epipterygoid is present (occurs also at node (occurs also at node 7, infrenatum and nigricans). 3 and in steindachneri), - 75(2) postorbital bar elegans: - 36(1) vomer contacts prefrontals (a less than one-fifth of orbit width (occurs also in unique reversal), - 68(1) epipterygoid, if present, spiniferus, sinensis, and subplanus. swinhoei: - always contacts the palatine (occurs also at node 32(2)jugal contacts squamosal in one-halfof sam- 9). frenatum: - 53(4) foramen palatinum poste- ple (occurs also at node 11 and in muticus), - rius consists of many small openings (occurs also 41(2) dorsal edge of apertura narium externum in aubryi), - 68(3) epipterygoid, if present, never weakly laterally emarginate (a reversal that occurs contacts the palatine (occurs also at node 7, in elsewhere only in euphratricus), - 54(2) foramen nigricans and senegalensis). indica: - 36(2) vomer palatinum posterius forms in palatine only (occurs never contacts prefrontal (occurs also at node 3), also at node 2 and in sinensis). spiniferus: - 75(2) - 65(3) premaxilla usually absent, - 71(3) epi- postorbital bar less than one-fifth of orbit width pterygoid always contacts prootic anterior to fo- (occurs also in sinensis, muticus, and subplanus), ramen nervi trigemini (occurs also in steindach- - 70(2) when epipterygoid is present, pterygoid ner), - 73(3) epipterygoid never fuses to pterygoid contacts foramen nervi trigemini between epi- (occurs also at nodes 1 1 and 18 and in cartilagi- pterygoid and parietal or not at all (occurs also in neus), - 74(0) intermaxillary foramen less than 7 sinensis). euphraticus: - 41(2) dorsal edge ofaper- percent of primary palate length, - 75(0) post- tura nariun externum weakly laterally emarginate, orbital bar twice length of orbit. cartilagineus: - a reversal that occurs elsewhere only in swinhoei). 67 68 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 186

1 6

Fig. 27. The most parsimonious cladogram for 91(2) two or more ossifications in second branchial extant soft-shelled turtles based on 13 characters horn, - 113(2) coracoid longest of three pectoral ofthe mandible and nonshell postcrania. Evidence processes (occurs also in punctata). Node 7: - for each node is as follows: Node 1: - 79(3) ent- 95(2) a strong ridge present in a depression on the epicondylar foramen never closed (occurs also in symphysis. Node 8: - 87(2) a distinct ventral keel the Staurotypinae and in Cheloniidae), - 80(2) present on the posterior end of the eighth cervical hyperphalangy of manus digits 4 and 5, pes digit (occurs also at node 13), - 90(3) eight ossifications 4 (absent only in senegalensis), - 82(2) three digits in corpus hyoidis (occurs also at node 11 and in clawed, - 84(2) centrum of eighth cervical not in gangeticus). Node 9: - 88(2) strong dorsal pro- contact with centrum of first body vertebra, - cesses on posterior cervicals (occurs also at node 85(2) no ventral process ofeighth cervical, - 90(2) 4), - 92(2) ossifications of second branchial horn six or more ossifications in corpus hyoideum, - very broad and strongly sutured, - 95(1) no ridge 96(2) foramen nervi auriculotemporalis usually on symphysis (a unique reversal), - 112(2) angle with two lateral openings (occurs also in emydids of acromion process to scapula approaches that of and some pleurodires), - 101(2) ilia curve pos- coracoid to acromion (occurs also at nodes 5 and teriorly, - 102(2) ilia are not expanded distally 10). Node 10: - 12(2) angle of acromion process (occurs also in all Kinosternidae), - 106(2) pec- to scapula approaches that of coracoid to acro- tineal processes and interpubic suture lie in a single mion (occurs also at nodes 5 and 9). Node 11: - plane (occurs also in Claudius), - 108(2) pectineal 90(3) eight ossifications in corpus hyoidis (occurs processes equal to or wider than interpubic con- also at node 8 and in gangeticus). Node 12: - tact. Node 2: - 93(2) basihyals in close contact 91(3) seven or more ossifications in second bran- and projecting anteriorly, - 98(2) foramen inter- chial hom (occurs also in gangeticus and spinifer- mandibularis caudalis never enclosed by preartic- us), - 109(2) metischial processes not well de- ular (occurs also in indica, formosus, and swin- veloped (occurs also at node 2). Node 13: - 87(2) hoei), - 109(2) metischial processes very weakly distinct ventral keel on posterior end of eighth developed (occurs also at node 12). Node 3: - cervical (occurs also at node 8). Specific characters. 107(1) ischia extend slightly into thyroid fenestra punctatus: - 113(2) coracoid longest of three pec- (reversal of feature shared by Staurotypinae, Ca- toral processes (occurs also at node 6). indica: - rettochelyidae, and Trionychidae). Node 4: - 88(2) 98(2) foramen intermandibularis caudalis never strong dorsal processes present on posterior cer- enclosed by prearticular (occurs also at node 2 and vicals. Node 5: - 112(2) angle ofacromion process in formosus and swinhoei). hurum: - 91 (1) only to scapula approaches that of coracoid to acro- one ossification in second branchial horn (a unique mion (occurs also at nodes 9 and 10). Node 6: - reversal). gangeticus: - 90(3) eight ossifications 1987 MEYLAN: TRIONYCHIDAE 69

Fig. 27 (continued). acromion process to scapula angle (character in corpus hyoidis (occurs also at node 8 and node 112), each identify a separate clade within 11), - 91(3) seven or more ossifications in the the Cyclanorbinae. second branchial horn (occurs also at node 12 and in spiniferus). formosus: - 98(2) foramen inter- Among the Trionychinae, one large subset mandibularis caudalis never enclosed by preartic- of taxa, the four Indian species plus Trionyx ular (occurs also at node 2 and in indica and swin- formosus, T. cartilagineus, Chitra indica, and hoei). spiniferus: - 91(3) seven or more ossifica- Pelochelys bibroni are recognized as a single tions in second branchial horn (occurs also at node clade largely on the basis of a symphyseal 12 and in gangeticus). swinhoei;- 98(2) foramen ridge (character 95). Four characters of the intermandibularis caudalis never enclosed by nonshell postcrania support monophyly of prearticular (occurs also at node 2 and in indica Chitra and Pelochelys. and formosus). The remaining trionychine species always include three additional clades. Trionyx mu- EVIDENCE FROM NONSHELL ticus and T. spiniferus share a rare configuration of the scapula (character 1 12). T. sub- POSTCRANIA AND LOWER JAW planus, T. euphraticus, T. swinhoei, and T. Only 13 characters of the lower jaw and ferox have eight ossifications of the corpus nonshell postcrania were found to display hyoidis (character 90), also found in T. car- useful interspecific variation among living tilagineus, Chitra, and Pelochelys. T. euphra- trionychids. This is far too few to allow com- ticus and T. ferox have a high number of plete resolution of the relationships of the ossifications in the second branchial horn Recent Trionychidae. Two pairs of species (character 91) and lack distinct methishial share identical character state distributions processes (character 109). (Cycloderma aubryi and Cycloderma frena- Although variation in the characters of the tum; Trionyx nigricans and T. leithii) and lower jaw and nonshell postcrania are insuf- three other species share another distribution ficient to allow formulation of an indepen- (T. steindachneri, T. sinensis, and T. triun- dent arrangement of the Recent trionychids, guis). Furthermore, two additional species, certain of these characters are important in T. swinhoei and T. formosus, have numerous corroborating clades identified by the shell missing values. The lack of resolvability and and skull data sets. Also, some characters the presence of many missing values result which have proven unimportant at this level in hundreds of equally parsimonious trees. are essential to formulation of a hypothesis But even among the numerous trees are some for the higher relationships of the Tri- consistently repeated nodes. onychidae. Examination of a large subset (N = 45) of these trees reveals that nine clades appear in FORMULATION OF A GENERAL every one. These provide important evidence HYPOTHESIS OF RELATIONSHIPS FOR for intrafamilial relationships and are shown THE TRIONYCHIDAE in a consensus tree (fig. 27). Most importantly, the Cyclanorbinae and Trionychinae The methods available for constructing are recognized in every case. The former has consensus trees (Adams, 1972 and Nelson, a unique configuration of the corpus hyoidis 1979) will not completely resolve the rela- (character 93), lacks distinct metischial pro- tionships among Recent soft-shelled turtles. cesses (character 109), and never has the fo- The Adams (1972) method combines infor- ramen intermandibularis caudalis defined by mation from nodes present in every rival tree. bone (character 98). The latter has multiple There is only one node, that representing the ossifications of the second branchial horn Trionychinae, found in all three fundamental (character 9 1) and the coracoid is longer than cladograms. The Nelson (1979) method com- the scapula (character 1 13) in every case (and bines replicated nodes as the foundation for also in Lissemys punctata). a consensus tree; uncombinable nodes are A unique reversal to the primitive condi- discarded and combinable nodes, which are tion of ischial projections into the thyroid unreplicated but compatible with one another, fenestra (character 107) and reduction of the are added to the replicated nodes. Only six 70 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 1 86 nodes are replicated in two or more of the Cyclanorbis (elegans plus senegalensis) is fundamental cladograms in this study and considered to be monophyletic. Monophyly four combinations of combinable unrepli- of the Cyclanorbinae is indicated in all six cated nodes can be added to produce a con- equally parsimonious trees based on the com- sensus tree which contains an equal amount bined data set. of cladistic information (an equal number of Resolution of the Cyclanorbinae is best nodes). completed by recognizing three monophylet- As an alternative, I have made a clade-by- ic genera, Lissemys (L. punctata), Cyclanor- clade comparison of the trees resulting from bis, and Cycloderma (aubryi plus frenatum), analysis of the shell data (fig. 25) to that re- with Lissemys being the sister group to the sulting from the data on the skull (fig. 26) and other genera. This arrangement requires that the mandible and nonshell postcrania (fig. 27). two steps be added to account for indepen- These results are then compared to those dent acquisition ofepiplastron shape and shell based on a separate PAUP analysis of all three shape (characters 19 and 25) in Lissemys and data sets combined (figs. 33, 34). Cycloderma. But the retention of the shell All three cladograms based-on independent topology would require independent acqui- data sets and those from the combined data sition of seven characters in Cycloderma and set consist ofbasal cyclanorbines, and a series Cyclanorbis and would add seven evolution- ofsimilar combinations ofIndian, Asian, and ary steps. Among the characters supporting North American species. It is simplest to monophyly of Cyclanorbis plus Cycloderma compare and combine results by proceeding are the reduced size ofthe coracoid (character up the cladogram. 1 3), medial curvature of the ilia (lost in Cyc- CYCLANORBINAE: Monophyly of the Cyc- lanorbis elegans; character 109), the presence lanorbinae has been advocated by several of a small and multiply divided foramen pal- students of trionychid systematics (Boulen- atinum posterius (character 53), and exclu- ger, 1889; Deraniyagala, 1939; Loveridge and sion of the quadrate from the trigeminal fo- Williams, 1957; Meylan, 1985). It is sup- ramen by the epipterygoid (character 71). ported strongly by the skull and nonshell data Three ofthe four species also lack prefrontal- sets (figs. 26, 27) but does not appear in the vomer contact, an absence found elsewhere arrangement based on the shell alone (fig. 25). only in Chitra indica (character 36). As pointed out in Meylan (1985) the unique Monophyly of Cyclanorbis is suggested by cyclanorbine xiphiplastral-hypoplastral joint ischial extension into the thyroid fenestra and early fusion of the hyo- and hypoplastra (character 107), reduced angle of the acro- (characters 10, 13) can be considered shared mion process to body of scapula (character derived characters for the subfamily rather 112), wide nuchal (character 1), united cos- than unique reversals for the Trionychinae tiform processes (character 2), and the loca- as shown in figure 25. These two characters, tion of the first thoracic vertebra in the in combination with the unique cyclanorbine middle of the nuchal bone (character 3). Cy- hyoid (character 93) restriction ofthe fenestra cloderma has a unique condition of the fo- postotica by an ascending pterygoid arch ramen palatinum posterius: it is represented (character 58), the absence of distinct me- by many very fine openings hardly distin- tishial processes (character 109), and other guishable from the nutritive foramina of the characters of the skeleton and soft parts (in- palate (character 53). The two species of the cluding femoral flaps) suggest that recogni- genus also share characters of shell shape and tion of a monophyletic Cyclanorbinae would epiplastron shape (characters 19, 25), which ultimately lead to a more parsimonious ar- are found also in Lissemys, and the presence rangement of the Trionychidae. If the shell of enlarged dorsal processes on the cervical arrangement (fig. 25) is used, the distribution series which occur elsewhere only in Chitra of seven nonshell characters common to these indica and Pelochelys bibroni (character 88). five taxa would require 21 evolutionary steps. The six equally parsimonious cladograms On the other hand addition of the shell data for the combined data set match three ar- to the skull arrangement would require only rangements of the Cyclanorbinae (fig. 29) to seven added steps, provided that the genus two arrangements of the Trionychinae (fig. 1987 MEYLAN: TRIONYCHIDAE 71

Fig. 28. A cladogram of 20 living species of soft-shelled turtles from Meylan (1985). It is based on 16 characters of the shell, a subset of those shell characters used in the current study. Evidence for the nodes is given in Meylan (1985). 30). One of the alternative cyclanorbine ar- support monophyly of Cycloderma (fig. 29B) rangements is that advocated above (fig. 29B). versus those which support monophyly of The other two require either a paraphyletic Cycloderma aubryi plus Cyclanorbis (fig. 29C) Cyclanorbis or a paraphyletic Cycloderma. provides useful results relevant to determin- Choice between these equally parsimoni- ing the relative reliability of these two alter- ous arrangements for the Cyclanorbinae rests native arrangements. The two characters on further considerations of the characters. which argue for monophyly of Cycloderma Variability in the number ofpleurals that meet include one unique evolutionary event, the on the midline (character 16) provides usefil reduction ofthe foramen palatinum posterius data that enhance the argument for recogni- to a series of fine openings (character 53), and tion of a monophyletic Cyclanorbis. The a feature which occurs elsewhere on only one modal condition ofthe neural series was used occasion, the presence of large dorsal spines to score taxa in table 3. However, the highly on the cervical vertebrae (fig. 20, character derived condition (state 4 of character 16), 88). The average consistency of these char- common in Cyclanorbis senegalensis, is also acters is 0.750. The average consistency of known to occur in Cyclanorbis elegans (see the three characters which support mono- section on neurals under variation in shell phyly of Cycloderma aubryi and Cyclanorbis morphology). Using Cartmill's (1978) phi- (fig. 29C) is much less, 0.431. These include losophy, that occasionally derived is in fact anterior location ofthe first thoracic vertebra derived, the rare occurrence ofa high number (character 3, C = 0.667), location of neural of pleurals meeting at the midline in Cycla- reversal (character 17, C = 0.375), and emar- norbis elegans reinforces the suggestion of gination of the prefrontals in the apertura monophyly for this genus which appears in narium externum (character 41, C = 0.250). two ofthe three alternative topologies for the On the strength of its higher consistency at Cyclanorbinae (fig. 29). the critical level (see Wheeler, 1986), it is Recognition of a monophyletic Cyclanor- suggested that the arrangement of the Cyc- bis reduces the choice of topologies for the lanorbinae that appears in figure 29B is the Cyclanorbinae to those shown in figure 29B most reliable hypothesis. and C. Examination of the characters which TRioNYcHINAE: The shell (fig. 25) and both 72 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 186

to neural six or seven and the presence of A multiple ossifications ofthe second branchial horn (characters 17 and 91). Four other features of the Trionychinae appear independently in one or both Cyclanorbis species (characters 1, 2, 21, and 23). The basic difference between the arrangement of the Trionychinae determined from shell versus skull data is the combination of the Asian and North American clades to the exclusion of the Indian clade in the shell arrangement and the combination of the In- dian, North American, and parts ofthe Asian clades to the exclusion of Chitra, Pelochelys, B and Trionyx cartilagineus in the skull arrangement. These differences are based on very few characters. More importantly, the four major clades which appear in the analyses of all three data sets combined always appear in either the skull or shell arrangement or both. At this point it seems best to consider the evidence for recognition ofthese four major clades within the Trionychinae. Consid- eration of a hypothesis about their interre- lationship can then follow. Four groups of species within the Tri- onychinae are represented as distinct clades C or are in close proximity in at least two of the three arrangements based on the three independent data sets and in all most parsimonious arrangements based on united data sets. These are termed the North American clade, the Indian clade, the Trionyx cartilagineus clade, and the T. steindachneri clade. The North American clade includes three Old World species, Trionyx triunguis, T. euphraticus, and T. swinhoei, as well as the three North American forms, T. ferox, T. muticus, Fig. 29. The three alternative topologies for and T. spiniferus. This clade also includes T. the subfamily Cyclanorbinae, each of which ap- sinensis in the arrangement based on shell pears in two of six equally parsimonious clado- data. All members of this group have eight grams of the Trionychidae based on combined or fewer neurals (character 14), deeply emar- skull, shell, and nonshell postcranial evidence. ginate prefrontals (character and Based on details of character 16 and higher inter- 41), a large nal consistency of critical characters, alternative contribution by the parietal to the processus B is used in the solution cladogram. trochlearis oticum (character 78). Except for T. triunguis, the members of this clade also have a large foramen intermaxillaris (char- nonshell arrangements (figs. 26, 27) support acter 74), second branchial horns which os- a monophyletic Trionychinae. In all, nine sify from seven or more centers (character characters support the recognition of this 9 1), and small to absent eighth pleurals (char- subfamily (figs. 33, 34). Unique features of acter 8). the Trionychinae include advancement ofthe The Indian clade includes Trionyx gan- point of reversal ofneural orientation at least geticus, T. leithii, T. hurum, and T. nigricans. 987 MEYLAN: TRIONYCHIDAE 73

and some of the members of the T. stein- NORTH dachneri group may be included in the Indian :ARTILAGINEUS AMERICAN STEINDACHNERI clade. GROUP GROUP GRO6P The Trionyx steindachneri group appears to include T. sinensis and T. subplanus. Al- INDIAN though these three taxa are not combined in GR6UP any ofthe three cladograms based on the three separate data sets, they form a monophyletic group in all six of the equally parsimonious cladograms resulting from analysis of all data combined (figs. 30, 33, 34). The most important character of this group is the unique NORTH division of the fenestra postotica by a de- CARTILAGINEUS AMERICAN STEINDACHNERI scending process of the opisthotic in T. si- GROUP GROUP GROUP nensis, T. steindachneri, and T. subplanus. Furthermore, in T. sinensis the pterygoid contacts the foramen nervi trigemini anterior INDIAN to the epipterygoid, unlike the condition in GROUP the members of the North American clade in which the contact is posterior to the epipterygoid (see discussion of character 70). T. si- Fig. 30. The two alternative topologies for the nensis also lacks the high number of ossifi- ubfamily Trionychinae, each ofwhich appears in cations in the cornu branchiale II, the hiree of six equally parsimonious cladograms of significant contribution of the parietal to the hie Trionychidae based on combined skull, shell, processus trochlearis oticum, the large fora- nd nonshell postcranial evidence. No supple- men intermaxillaris, and the secondarily en- aentary evidence is available to support one of larged vomer found in all members of the hese arrangements over the other. North American clade (characters 91, 78, 74, 48, and 49). Recognition ofa clade consisting of T. sinensis, T. steindachneri, and T. sub- .he evidence that this group should be rec- planus requires that the highly variable neu- ignized comes entirely from the shell. All ral formula with the last reversal in neural our species have a maximum of five plastral orientation occurring at neural six (characters allosities, epiplastral extensions of inter- 15 and 17) and the reappearance ofcallosities nediate length, and two neurals between the on all plastral elements (character 9) occur trst pair of pleurals (characters 4, 9, and 20). independently in T. sinensis and in the North he presence oftwo neurals between the first American clade. However, reversal of reduc- 'air of pleurals may be primitive for the tion in the eighth peripheral and of sexual rionychinae but in that case an extra neural size dimorphism which are required in the aust have been added to the anterior end of shell arrangement are not required if T. si- he neural series in the common ancestor of nensis is withdrawn from the North Ameri- 11 trionychids. Only one appears between the can clade. Lrst pleurals in carettochelyids, kinostemids, The last ofthe four groups ofspecies within .nd dermatemydids. The addition of neural the Trionychinae includes Trionyx cartila- ne in the ancestral trionychid and the sub- gineus, Chitra indica, and Pelochelys bibroni. equent fusion of neurals one and two called These three species have the foramen pos- or in Meylan (1985) are two independent terius canalis carotici interni lying within, vents. However, the appearance of two rather than below, the lateral crest of the tu- Leurals between the first pleurals could al- berculum basioccipitale, a condition seen ernatively be explained by independent elsewhere only in the single available skull of vents in the Cyclanorbinae and in the Indian T. nigricans (character 60). The epipterygoid orms of Trionyx. In the various arrange- frequently contacts the prootic anterior to the aents under consideration here T. formosus foramen nervi trigemini (character 70), and 74 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 186

the eighth cervical vertebra has a distinct sinensis. Only the latter character is present ventral ridge (character 87) in all three. Fur- in T. steindachneri and T. subplanus, but the thermore, these taxa all have a hyoid with distribution of other characters suggests that eight elements in the corpus hyoidis which the absence of the former is best considered occurs elsewhere only in T. subplanus and in as a reversal. three species of the North American clade. This arrangement (fig. 31) is the most par- The highly derived nature of Chitra and Pelo- simonious one that will preserve the four chelys is suggested by their many shared de- species groups as monophyletic units. It is rived features and the unique features of Chi- four steps longer than the two shortest trees tra. based on analysis of the skull, shell, mandi- The shell characters that conflict with the ble, and nonshell postcrania combined. nonshell evidence for monophyly of these The two alternative arrangements of the three taxa are relatively minor. An extra pos- Trionychinae based on the analysis of the terior neural may appear at times in Chitra combined data sets differ only in the place- indica and Trionyx cartilagineus and neural ment of the four trionychine clades (figs. 30, reversal may occur one neural more poste- 33, 34). In both, the Indian species group is riorly in some cases (characters 14 and 17). paraphyletic and the only difference is that The clearest conflict in character distribution the North American forms are the sister group is the presence ofelongate anterior epiplastral to the Trionyx cartilagineus group on the one projections (character 20) in T. cartilagineus hand, and to the T. steindachneri group on and in the Indian and T. steindachneri groups. the other. No supplementary evidence is Recognition of these groups requires that available to support one of these arrange- elongate epiplastra arise independently on ments over the other. Consequently, until ad- three occasions. ditional data can be collected and analyzed, The resolution of the species of the Tri- the arrangements shown in figures 33 and 34 onychinae into four clades seems clear and it must be considered equally plausible, most results in the recognition of groups which parsimonious hypotheses for the interfami- other authors have recognized and even lial relationships of the Trionychidae. The named in the past. To finish the task of de- revised classification which follows reflects termining the best hypothesis for relation- the uncertainties which remain in our un- ships among all members of this subfamily, derstanding of trionychid relationships (fig. it is necessary to identify the interrelation- 32). ships ofthese four clades. Unfortunately, there are few characters which contribute to the understanding of the relationship of these COMPARISON OF RESULTS TO THE clades to one another and several alternative PREVAILING HYPOTHESES OF hypotheses are possible. TRIONYCHID RELATIONSHIPS Based on the presence ofa symphyseal ridge Although there is extensive literature on (character 95) (which is absent in species with the taxonomy of soft-shelled turtles, few au- a short symphysis or reduced overall size) thors have considered the systematic rela- and a constricted basisphenoid (character 64), tionships of all of the family members. The all of the Indian and Asian forms could be few exceptions are Hummel (1929), Love- the sister group of the North American clade ridge and Williams (1957), and De Broin (fig. 3 1). Within this Indian and Asian clade, (1977). Of these, the Loveridge and Williams the Trionyx cartilagineus group stands out as treatment gives the most complete consid- being highly derived. A sister group to the T. eration of intrafamilial relationships. cartilagineus group could be defined on two These three major systematic studies all features of the skull: contact of the jugal and recognize at least three of the five species squamosal across the quadratojugal (char- groups thought to represent monophyletic (or acter 32) and contact ofjugal and parietal on paraphyletic) clades in the current study. The the skull surface (character 34). These char- Cyclanorbinae and the Indian and North acters occur in some individuals of nearly American groups retain their identity in all every species in the Indian clade and in T. three. The uniqueness of the genera Peloche- 1 987 MEYLAN: TRIONYCHIDAE 75

Fig. 31. The topology of the most parsimonious cladogram that preserves monophyly of all four trionychine clades identified during this study. This arrangement is four steps longer that those shown in figures 33 and 34. lys and Chitra is recognized in each, as is the chosen as the best solution. However, they possible relationship of Trionyx sinensis to supported monophyly of Cyclanorbis and T. steindachneri. Cycloderma, as is suggested by the data con- Since the time of Boulenger (1889) and Ly- sidered in the current study. dekker (1889), soft-shelled turtles that hide The Indian clade is recognized in all three their hind feet with flaps of skin have been previous systematic studies of the family. It recognized to be unique relative to other soft- has been based in part on the presence of a shelled turtles. Only De Broin (1977) ques- preneural although this may be primitive for tioned the monophyletic nature of this the family. Hay (1904) proposed the name subfamily. The 12 shared, derived features Aspideretes for those fossil and Recent trion- of this subfamily (figs. 33, 34) strongly sup- ychine species with a preneural. Hummel port its continued recognition. Furthermore, (1929) endorsed the use of this term as a the nine derived features ofthe Trionychinae subgenus, and De Broin (1977) recognized it indicate monophyly for the remaining trion- alternatively as a valid genus or subgenus. In ychids which have previously been placed spite of its apparent paraphyletic nature, rec- together without attention to their unique ognition of this distinctive taxon may best common ancestry. promote a more complete understanding of Loveridge and Williams (1957) detailed the trionychine relationships. relationships of the African members of the De Broin (1977) and Loveridge and Wil- Cyclanorbinae in terms of a progression of liams (1957) found Trionyxformosus and T. what they considered to be the most primi- cartilagineus to be closely related to the In- tive form, Cyclanorbis elegans, to the most dian clade. The results of this study suggest derived form, Cycloderma aubryi, based on that T. formosus is the sister group ofthe four three skull characters. The arrangement of Indian species (but that it does not share the the Cyclanorbinae given in their figure 50 features of Aspideretes). T. cartilagineus is (reproduced here as a cladogram in fig. 1) is thought to share a unique common ancestor identical to one of three alternatives for the with Chitra and Pelochelys. Cyclanorbinae derived here (fig. 29A) but not In past studies the North American clade 76 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 186

Trionychidae Fig. 32. A cladogram of trionychid relationships derived from the classification supported by this study. The use of a single branch point for the four tribes within the Trionychinae reflects uncertainty about the interrelationships of these four monophyletic groups. is as frequently recognized as the Indian clade. strict the use of the name Platypeltis to the The present analyses suggest that it includes three North American forms and resurrect Trionyx triunguis, T. euphraticus, T. swin- the name Rafetus Gray 1864 for T. swinhoei hoei, and the three living North American and T. euphraticus. Although Rafetus Gray species, T. muticus, T. spiniferus, and T. fe- could be applied to these two Old World rox. No previous study has included T. triun- members of this clade, Apalone Rafinesque guis in this group. Loveridge and Williams 1832 (Trionyx spiniferus LeSeuer 1827 type (1957) placed T. triunguis in a sister group species) has priority over Platypeltis Fitzinger to the North American clade along with T. 1835 and would have to be applied to the sinensis and T. steindachneri (fig. 1). These three North American forms. three species are united only because they Fortunately, the systematic position of Tri- each fail to share features of the distinctive onyx triunguis is clear. It can stand alone in groups which these authors recognized. De the arrangement of the family as described Broin (1977) considered T. triunguis as the above. This is important taxonomically be- remnant of a group that evolved indepen- cause it is the type species of Trionyx. The dently from that which led to the North long muzzle of this species makes it phenet- American forms. Based on the osteological ically distinct and the separation of the ex- features considered here, T. triunguis is best occipital from the pterygoid by the basisphe- considered the sister group of the remainder noid (character 63) is unique and makes it of the North American clade. The remainder cladistically recognizable. of this clade is recognized in the three pre- In past considerations of trionychid rela- vious systematic works and the name Platy- tionships the species Trionyx sinensis and T. peltis Fitzinger 1835 was applied to it by steindachneri appear to have been left over Hummel (1929). De Broin (1977) would re- after other more distinctive taxa had been 1 987 MEYLAN: TRIONYCHIDAE 77 extracted from the Trionychinae. Loveridge TABLE 22 and Williams (1957) mentioned the unique Summary of Classification of the Trionychidae feature shared by these two taxa (and also T. Suggested by This Study subplanus), division of the fenestra postotica Trionychidae (Fitzinger, 1826) Bell, 1828 by a ventral process ofthe opisthotic, but they Cyclanorbinae Hummel, 1929 do not make full use of this unique quality. Cyclanorbini (Hummel, 1929), New Rank In addition to this skull character, these two Cyclanorbis Gray, 1854 species and T. subplanus share characters of Cyclanorbis senegalensis (Dumeril and Bibron, reduced total size and an extremely short nu- 1835) chal bone. Smith and Smith (1980) indicated Cyclanorbis elegans (Gray, 1869) name Geoffroy has Cycloderma Peters, 1854 that the generic Amyda Cycloderma aubryi (A. Dumeril, 1856) Trionyx cartilagineus as its type species and Cycloderma frenatum Peters, 1854 thus cannot be applied to this clade as has Lissemydini (Williams, 1950) New Rank been suggested by De Broin (1977) and Hum- Lissemys Malcom Smith, 1931 mel (1929). The first available name is Pelo- Lissemys punctata (Lac6p6de, 1788) discus Gray 1844 for which T. sinensis is the Trionychinae (Fitzinger, 1826) Lydekker, 1889 type species. Chitrini (Gray, 1870) New Rank The last of the four trionychine clades rec- Chitra Gray, 1844 ognized in the current study includes Pelo- Chitra indica (Gray, 1831) chelys, Chitra, and Trionyx cartilagineus. Pelochelys Gray, 1864 More than 100 years ago Gray (1873a) rec- Pelochleys bibroni (Owen, 1853) Amyda Geoffroy, 1809 ognized a unique relationship between Chitra Amyda cartilaginea (Boddaert, 1770) and Pelochelys by making them the only Aspideretini, New Tribe members of his subfamily Chitraina of the Aspideretes Hay, 1904 family Chitridae. Although no authors have Aspideretes gangeticus (Cuvier, 1825) followed this arrangement, none have dis- Aspideretes hurum (Gray, 1831) puted it. Aspideretes leithii (Gray, 1872) The sister group relationship of Trionyx Aspideretes nigricans (Anderson, 1875) cartilagineus to Chitra and Pelochelys pro- Nilssonia Gray, 1872 posed here is novel. But based on a unique Nilssoniaformosa (Gray, 1869) location of the foramen posterior canalis ca- Trionychini (Fitzinger, 1826) New Rank Trionyx Geoffroy, 1809 rotici intemi (character 60), frequent contact Trionyx triunguis (Forskil, 1775) of the epipterygoid and prootic anterior to Rafetus Gray, 1864 the foramen nervi trigemini (character 71), Rafetus euphraticus (Daudin, 1802) absence of contact of epipterygoid and pal- Rafetus swinhoei (Gray, 1873) atine (character 68), and the presence of a Apalone Rafinesque, 1832 fine ridge on the centrum of the eighth cer- Apaloneferox (Schneider, 1783) vical vertebra (character 87), the sister rela- Apalone spinifera (Le Sueur, 1827) tionship of T. cartilagineus to these unique Apalone mutica (Le Sueur, 1827) genera is well supported. Recognition of the Pelodiscini, New Tribe T. as a seems Pelodiscus Gray, 1844 cartilagineus clade single genus Pelodiscus sinensis (Wiegmann, 1835) undesirable given the established quality of Dogania Gray, 1844 the names Pelochelys and Chitra. But T. car- Dogania subplana (Geoffroy, 1809) tilagineus deserves distinction from the rest Palea, New Genus of the genus Trionyx. In this case the generic Palea steindachneri (Siebenrock, 1906) name Amyda Geoffroy, for which Testudo cartilaginea Boddaert (1770) is the type species, should be applied to T. cartilagineus (Smith and Smith, 1980). qualities ofthese clades are not currently con- In summary, the clades recognized by phy- veyed by the broad use of the name Trionyx logenetic analysis are in nearly every case not but could be by the use of the available ge- totally novel. All have had generic or subge- neric names as in the classification which fol- neric names applied to them. The unique lows (summarized in table 22). If more com- 78 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 186 plete resolution of the interrelationships of the pubic bones lie in a single plane as appears the four identified trionychine clades can be to be the case early in ontogeny of other tur- achieved, further increase in information tles. Furthermore, ossification of the prepu- content of trionychid classification could re- bic region, which occurs in most living cryp- sult from the use of supertribes to contain todires, never occurs in trionychids. The tribes of unique common ancestry. absence of other paedomorphic features of soft-shelled turtle morphology suggests that developmental truncation has not been an TRENDS AND MECHANISMS IN overriding influence on the evolution of the SOFT-SHELLED TURTLE EVOLUTION group. Although it is possible to trace the changes The most completely described adaptive in character states during the course of evo- hypothesis for the unique shell form of trion- lution of trionychids, many possibilities exist ychids is that of Pritchard (1984). He sug- that might explain why these changes have gested that Chitra is the best model for the occurred. Three adaptive scenarios could ex- ancestral trionychid, and that the unique body plain portions of the unique morphology of form of trionychids is an adaptation for a trionychids: (1) selection for greater snapping rapid predatory strike (one of his three listed ability (Pritchard, 1984); (2) selection for high- adaptations for piscivory). His evidence is speed swimming (Pritchard, 1984; personal partly based on the similarity of the skull of obs.); and (3) selection for greater aquatic fos- Chitra to that of Chitracephalus dumonli soriality (Pritchard, 1984; Bramble, personal Dollo 1884 from the Jurassic or Cretaceous commun.). of Europe, and partly on his observation that The apparently critical evolutionary step Chitra is the most developed piscivore among which allows the unique loss of peripherals the trionychids and that other forms have in trionychids occurs in carettochelyids. This secondarily become more generalized. is the very tight and broad suturing of the rib Other than their similar skull shape, there heads to the vertebral centra. The develop- is nothing to suggest that Chitracephalus is ment of massive rib heads provides a struc- related to the trionychids (Gaffney, 1979b). tural alternative to the use of the plastron (via Pritchard himself stated that the long, narrow the peripherals) as a tension member (Rich- skull found in these two forms appears a mond 1964; Bramble, personal commun.). number of times in turtle evolution. He cites The peripherals are not strongly sutured to Glyptops (a pleurostemid) and Deirochelys (an the pleurals in Carettochelys and it is unlikely emydid) as examples. The superficial simi- that the plastron is as effective a tension larity of Chitracephalus and Chitra goes be- member in this genus as it is in turtles with yond the overall skull shape: both have large solid pleuroperipheral and bridge contacts. and well-developed hyoids. However, judg- The absence of peripherals can most easily ing from unpublished stereo photographs of be explained by developmental truncation. the type of Chitracephalus, the corpus hyoidis In the embryonic turtle, ossification centers in the type is not composed of multiple os- in the disc margin (those which result in the sifications and what appears to be a jugal- peripherals, nuchal, and pygal bones) are the quadratojugal bar is actually the lower jaw. last to form (Zangerl, 1969). Consequently, Thus, Chitracephalus has continuous cheek the trionychid shell may be paedomorphic; and temporal emargination which is not that is, the final step in carapace development known elsewhere among the Cryptodira. never occurs. Further arguments against using Chitra as Paedomorphosis may be the mechanism the ancestral trionychid can be taken directly by which the unique trionychid shell mor- from the phylogenetic analyses conducted in phology evolved. However, few other fea- this study. The many unique features of Chi- tures of soft-shelled turtles can be ascribed tra (and Chitra plus Pelochelys) would have to a truncation of development. The only to be lost secondarily in all other trionychids. characters which might also be a result of A good example is the extensive postorbital paedomorphosis are those of the pubic ele- bar. The hypothesis supported by the phy- ments. As noted, the pectineal processes of logenetically analyzed data suggests that a very 1 987 MEYLAN: TRIONYCHIDAE 79 narrow postorbital bar first allowed contact ascribed to crypsis or to their swimming of the jugal and parietal and that expansion speed. Trionychids may be among the fastest of this contact is secondarily increased in swimming freshwater turtles (see Webb, 1962, Chitra and other species in the family with and references therein). It has been my ob- long, narrow skulls. Other features, including servation that Trionyx ferox is the fastest extensive hyperphalangy (Boulenger, 1889), swimming turtle that one encounters in clear the presence of large dorsal spines on the fifth Florida spring runs. Selection for better and sixth cervicals, the narrow symphysis, swimming ability could explain the acquisi- the very short nuchal bone with the first tho- tion of numerous derived features noted dur- racic vertebra located at the anterior margin, ing the course of this study, especially those and the unique hyoid with a massive corpus of the shell and girdles. hyoidis ofeight ossifications and large second Trends toward reduction in shell size, in- branchial arch of three strongly sutured os- cluding reduction in the number of periph- sifications, would all have to appear and then erals, neurals, and plastral callosities, and re- be lost in the course of trionychid evolution. duction in the size of the eighth pleurals and It is far more parsimonious to consider the the nuchal bone could all be attempts to light- genus Chitra as a highly specialized triony- en the shell, with shell streamlining as the chid (with all ofits derived features appearing result. Reduction of the bridge is important only once). Conversely, Pritchard's (1984) ar- in allowing maximum retraction of the hind gument that Lissemys punctata is the most limbs for a maximum power stroke in swim- derived of trionychids remains unsupported. ming (Zug, 1971). The view that it is the most primitive (Wal- Loss of epidermal scutes may also act to ther, 1922; Deraniyagala, 1939) is corrobo- reduce the weight of the shell. If Coldiron rated in the current study. (1974) is correct in his hypothesis that dermal Pritchard (1984) suggested that swimming bone sculpturing acts to disperse stresses on prowess and aquatic fossoriality are two sec- broad areas of dermal bone (crocodilian and ondary advantages of modification of shell labryinthodont skulls), sculpturing could be shape in trionychids. Bramble (personal an alternative shell-strengthening mecha- commun.) has also pointed out that fossorial nism to epidermal scutes in trionychids. activity is enhanced by the shape of the trion- Acquisition of hyperphalangy can be cor- ychid carapace. Certainly, the flattened body related with increased swimming prowess. form of trionychids provides reduced resis- Strong contact of the radius and ulna stiffens tance to motion through water, sand, or mud. the forearm and probably produces a better It is only after the loss of peripherals in trion- paddle in trionychids, carettochelyids, and ychids that there has been a remarkable de- cheloniids. The reduction of the transverse crease in the relative proportion of the total processes of the tenth thoracic vertebra that carapace made up by the bony disc. A con- occurs in all trionychoids might increase the comitant increase in the flexible margin, capacity ofthe pelvic girdle to rotate and thus which would assist in aquatic fossoriality, also contribute to the very long hind-limb power occurs at this stage, indicating that fossori- stroke of trionychids (Zug, 1971). The ex- ality may in fact be a secondary result of pe- panded pectineal processes of the pelvic gir- ripheral loss, and not necessarily the cause dle and the relatively enlarged coracoids both for their loss. provide additional surface area for muscle Although trionychids have reduced shells, attachment. Thus it appears that selection for they are found living with turtle-eating croc- improved swimming speed would account for odilians throughout much oftheir range. Their many of the derived features noted to occur survival under such circumstances may be in the Trionychidae. 80 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 186

'21

20 18 17

L12 '13 I 1

1 Fig. 33. One of two most parsimonious also at node 8 and informosus and steindachneri), arrangements of the living Trionychidae. Char- - 36(2) vomer not in contact with prefrontal (oc- acters supporting the nodes are as follows: Node curs also in indica and reverses in elegans), - 1: The evidence for monophyly of the Trionychi- 53(3) foramina palatinum posterius small and didae is summarized in table 21. Node 2: - 10(2) vided, - 69(2) no contact between pterygoid and hyoplastra and hypoplastra fuse just after hatch- foramen nervi trigemini when epipterygoid is ing, - 13(2) hypoplastra are lateral to xiphiplastra present (occurs also in muticus and steindachneri), at hypo-xiphiplastral union, - 14(2) eight or nine - 72(2) epipterygoid contacts prootic posterior to neurals (reduced from always nine) (occurs also at foramen nervi trigemini, - 100(2) ilia curve me- node 19 and in indica and leithii), - 16(2) eighth dially, - 113(1) coracoid shorter than either pro- pleural only or seventh and eighth pleurals meet cess of scapula (unique among trionychids). Node on midline (occurs also at node 1 1), - 17(1) neural 4: - 19(2) epiplastra I-shaped (occurs also in reversal always occurs at neural eight (may be punctata), - 25(2) carapace straight or concave primitive condition), - 34(2) jugal contacts pa- posterolaterally (occurs also in punctata), - 53(4) rietal on skull surface in one-halfof sample (occurs posterior palatine foramen consists of many small also at node 15 and in leithii and muticus), - 54(2) foramina, - 68(3) epipterygoid never contacts foramen palatinum posterius forms in palatine only palatine (occurs also at node 8 and in nigricans (occurs also in sinensis and swinhoei), - 58(2) and senegalensis), - 88(2) strong dorsal processes foramen jugulare posterius excluded from fenestra on cervicals (occurs also at node 9). Node 5: - postotica by pterygoid arching to contact opis- 2(2) anterior and posterior costiform processes thotic, - 68(2) epipterygoid excluded from con- united (occurs also at node 6), - 3(2) anterior edge tact with palatine in 50% of cases where it is pres- of first body vertebra is in the middle ofthe nuchal ent (occurs also at node 8), - 93(2) basihyals in bone (occurs also at node 6 and in aubryi), - close contact and projecting anteriorly, - 98(2) 107(2) no extension of ischia into thyroid fenestra foramen intermandibularis caudalis never en- (occurs also at node 6), - 112(2) angle ofacromion closed by prearticular (occurs also at node 12 and process to scapula approaches that of coracoid to in indica and formosus), - 107(1) ischia extend acromion (occurs also at nodes 9 and 14). Node into thyroid fenestra (reversal of a derived con- 6: - 1(3) nuchal at least three times wider than dition shared by most trionychids, carettoche- long (occurs also in senegalensis), - 2(2) anterior lyids, and staurotypine kinosternids, - 109(2) and posterior costiform processes united (occurs metischsial processes not well developed (occurs also at node 5), - 3(2) anterior edge of first body also at node 11). Node 3: - 5(4) no peripheral vertebra in the middle of the nuchal (occurs also elements (occurs also at node 6), - 34(3) jugal at node 5 and in aubryi), - 5(4) no peripheral always contacts parietal on skull surface (occurs bones (occurs also at node 3), - 9(3) four plastral 1987 MEYLAN: TRIONYCHIDAE 81

Fig. 33 (continued). reversal that occurs also in elegans). Node 10: - callosities (reversal to 5 occurs at node 16 and in 17(3) point of reversal of neural orientation at cartilagineus), - 17(3) neural series reverses at neural six or seven (occurs also at node 8), - 20(2) neural six or seven or anterior to that point, - anterior extension of epiplastra is intermediate. 21(2) depressions for ilia in eighth pleural absent Node 11: - 16(2) pleurals seven and eight or eight (occurs also in elegans), - 23(2) bridge short (oc- only meet on midline (occurs also at node 2), - curs also in elegans), - 41(2) dorsal edge of aper- 34(l) jugal never contacts parietal on skull surface tura narium externum weakly emarginate (occurs (a reversal that occurs also in cartilagineus). Node also in aubryi and senegalensis), - 64(2) basi- 12: - 15(2) neural reversal occurs at one of two sphenoid occasionally medially constricted, - adjacent neurals, - 32(1) jugal never contacts 73(3) epipterygoid never fuses to pterygoid, -91(2) squamosal (a reversal), - 41(3) dorsal edge of two or more ossifications in second branchial horn apertura narium externum strongly laterally emar- of hyoid, - 95(2) symphyseal ridge strong and ginate. Node 13: - 14(2) some individuals with present in a depression, - 107(2) no extension of only eight (rather than nine) neurals (fused one ischia into thyroid fenestra (occurs also at node and two counted as two) (occurs also at node 2 5). Node 7: - 4(2) first and second neurals fused and in bibroni and leithii), - 76(2) quadratojugal (occurs also at node 14), - 60(2) foramen pos- participates in processus trochlearis oticum (oc- terius canalis carotici interni occurs within lateral curs also in cartilagineus, elegans, andfrenatum). crest of basioccipital tubercle (occurs also in ni- Node 14: - 4(2) first and second neurals fused gricans), - 70(0) when epipterygoid is present (occurs also at node 7), - 9(3) four callosities pterygoid contacts foramen nervi trigemini be- present in plastron (occurs also at node 8 and in tween epipterygoid and quadrate or not at all (oc- formosus), - 95(1) symphyseal ridge absent (occurs also at node 17 and in leithiz), - 71(2) epi- curs also at node 8). Node 15: - 1(4) width of pterygoid contacts prootic anterior to foramen nuchal bone more than four times length (occurs nervi trigemini in about 50% of sample (occurs also in muticus), - 20(3) anterior extension of also in hurum), - 87(2) ventral keel on eighth epiplastra is long (occurs also in cartilagineus), - cervical present and limited to posterior end of 24(2) largest adult size 200 mm or less (occurs also centrum (occurs also at node 19), - 90(3) eight at node 21), - 34(2) jugal contacts paretal on ossifications make up corpus hyoidis (occurs also skull surface in one-half of sample (occurs also at at node 18 and in hurum and subplanus). Node 8: node 2 and in hurum and muticus), - 59(2) fo- - 9(3) four callosities present in plastron (occurs ramen jugulare posterius excluded from fenestra also at node 14 and informosus), - 17(3) reversal postotica by descending process ofopisthotic which of neural orientation occurs at neural six or seven reaches pterygoid, - 70(2) when epipterygoid is (occurs also at node 10), - 34(3) jugal always present, pterygoid contacts foramen nervi trigem- contacts parietal on skull surface (also occurs at ini between epipterygoid and parietal or not at all. node 3 and informosus and steindachnen), - 4 1(1) Node 16: - 17(2) neural reversal occurs at neural dorsal edge of apertura narium externum not seven (a reversal), - 69(2) no contact occurs be- emarginate (a reversal that occurs elsewhere only tween pterygoid and foramen nervi trigemini when in frenatum), - 48(1) vomer divides maxillae (a epipterygoid is present (occurs also at nodes 3 and presumed reversal that occurs at node 18 and in 21). Node 17: - 14(3) eight neurals, - 15(1) neu- senegalensis), - 49(1) vomer reaches intermax- ral reversal always occurs at same neural (a re- illary foramen (a presumed reversal that occurs versal that occurs also in steindachneri), - 20(1) also at node 18 and in punctata and senegalensis), anterior extension of epiplastra short (a reversal), - 64(1) basisphenoid not medially constricted - 64(1) basisphenoid not medially constricted (a (occurs also at node 17), - 68(3) epipterygoid reversal that occurs also at node 8), - 70(0) when never contacts palatine (occurs also at node 4 and epipterygoid is present, pterygoid contacts fora- in nigricans and senegalensis), - 88(2) strong dor- men nervi trigemini between epipterygoid and sal processes present on cervicals five and six (oc- quadrate or not at all (occurs also at node 7 and curs also at node 4), - 92(2) ossifications ofsecond in leithil), - 78(2) 22.1% or more of processus branchial horn broad and strongly sutured, - 95(1) trochlearis oticum is made up by parietal (occurs no symphyseal ridge (occurs also at node 14), - also in elegans and nigricans). Node 18: - 8(2) 112(2) angle of acromion process to scapula ap- eighth pleurals reduced or absent, - 48(1) vomer proaches that ofcoracoid to acromion (occurs also divides maxillae (a reversal that occurs also at at nodes 3 and 21). Node 9: - 32(2) jugal contacts node 8 and in senegalensis), - 49(1) vomer reach- squamosal in one-half of sample (occurs also in es intermaxillary foramen (a reversal that occurs muticus, sinensis, and swinhoei), - 64(3) basi- also at node 8 and in punctata and senegalensis). sphenoid medially constricted, - 68(1) epipter- - 74(2) average ratio of intermaxillary foramen ygoid always contacts palatine when present (a length to length primary palate about 0.60, - 90(3) 82 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 186

Fig. 33 (continued). dratojugal participates in processus trochlearis oti- eight ossifications in corpus hyoidis (occurs also cum (occurs also at node 13 and in cartilagineus at node 7), - 91(3) seven or more ossifications in and frenatum), - 78(2) 22.1% or more of pro- second branchial horn (occurs also in gangeticus), cessus trochlearis oticum made up by parietal (oc- - 109(2) metischial process not distinct (occurs curs also at node 17 and in nigricans). senegalensis: also at node 2). Node 19: - 9(4) two callosities - 1(3) nuchal more than three times wider than on plastron (occurs also in elegans), - 41(2) dorsal long (occurs also at node 6), - 7(2) prenuchal bone edge ofapertura narium extemum weakly laterally present (occurs also in punctata), - 9(0) nine cal- emarginate (a reversal that occurs also in gange- losities in plastron, - 14(5) seven or fewer neurals, ticus), - 87(2) weak ventral keel present on pos- - 16(4) pleurals in addition to numbers six, seven, terior end of eighth cervical (occurs also at node and eight meet at midline, - 48(1) vomer divides 7), - 98(2) foramen intermandibularis caudalis maxillae (occurs also at nodes 8 and 18), - 49(1) never enclosed by prearticular (occurs also at node vomer reaches intermaxillary foramen (occurs also 2 and informosus and indica). Node 20: - 15(3) at nodes 8 and 18 and in punctata), - 68(3) when position of reversal of neural orientation highly present epipterygoid does not contact palatine (oc- variable, often two reversals present (occurs also curs also at nodes 4 and 8 and in nigricans). punc- in sinensis), - 17(4) point of reversal of neural tata: - 7(2) prenuchal bone present (occurs also orientation at neural six, - 29(2) sexual dimor- in senegalensis), - 12(2) xiphiplastra fuse in large phism in disc length. Node 21: - 9(1) seven cal- adults (occurs also in aubryi), - 14(4) seven or losities in plastron of large adults (a reversal that eight neurals, - 19(2) epiplastra I-shaped (occurs occurs also in sinensis), - 24(2) largest adult disc also at node 4), - 25(2) carapace straight or con- length 200 mm or less (occurs also at node 15), - cave posterolaterally (occurs also at node 4), - 69(2) contact between pterygoid and foramen ner- 49(1) vomer reaches intermaxillary foramen (oc- vi trigemini is absent when epipterygoid is present curs also at nodes 8 and 18 and in senegalensis), (occurs also at nodes 3 and 16), - 75(2) postorbital - 65(2) premaxilla occasionally absent (occurs bar less than one-fifth of orbit diameter (occurs also in aubryi, frequently absent in indica). bibroni: also at node 16), - 90(2) six ossifications in corpus - 14(2) eight or nine neurals (occurs also at nodes hyoidis (a reversal), - 109(1) metischial processes 2 and 13 and in leithii), - 73(2) epipterygoid fuses present and distinct (a reversal), - 1 12(2) angle to pterygoid in adults only (occurs also in elegans, of acromion process to scapula approaches that of frenatum, gangeticus, muticus, subplanus, and coracoid to acromion (occurs also at nodes 3 and triunguis). indica: - 3(3) anterior edge of first body 8). Specific characters. aubryi:- 3(2) anterior edge vertebra at anterior edge ofnuchal, - 29(2) sexual of first body vertebra at middle of nuchal (occurs dimorphism in disc length, - 36(2) vomer does also at nodes 5 and 6), - 12(2) xiphiplastra may not contact prefrontals (occurs also at node 3), - fuse on midline (occurs also in punctata), - 65(2) 65(3) premaxillae usually absent, - 71(3) epi- premaxillae occasionally absent (occurs also in pterygoid contacts prootic anterior to foramen punctata), - 68(2) epipterygoid, if present, fails nervi trigemini (occurs also in steindachneri), - to contact palatine in one-half of sample (a rever- 74(0) intermaxillary foramen about 7% ofprimary sal). frenatum: - 3(1) anterior edge of first body palate length, - 75(0) postorbital bar about two vertebra lies at posterior edge of nuchal (a reversal times orbit width, - 98(2) foramen intermandibu- that occurs also in punctata), - 17(2) reversal of laris caudalis never enclosed by prearticular (oc- neural orientation occurs at neural seven (occurs curs also at nodes 2 and 19 and in formosus). also at node 16), - 41(1 ) dorsal margin ofapertura cartilagineus: - 20(3) long anterior projections of narium extemum is not emarginate (a reversal that epiplastra (occurs also at node 15), - 76(2) qua- occurs also at node 8), - 73(2) epipterygoid fuses dratojugal participates in processus trochlearis oti- to pterygoid in adults only (occurs also in bibroni, cum (occurs also at node 13 and in elegans, fre- elegans, gangeticus, muticus, subplanus, and triun- natum, and steindachnerz).formosus: - 1(2) nuchal guis), - 76(2) quadratojugal participates in pro- between two and three times wider than long (a cessus trochlearis oticum (occurs also at node 13 reversal that occurs elsewhere in steindachneri), - and in cartilagineus and frenatum). elegans, 9(3) four callosities in plastron (occurs also at nodes 9(4) two plastral callosities (occurs also at node 8 and 14), - 34(3) jugal always contacts parietal 19), - 21(2) no depressions for ilia on eighth pleu- on skull surface (also occurs at nodes 3 and 8 and rals (occurs also at node 6), - 23(2) bridge short in steindachneri), - 98(2) foramen intermandi- (occurs also at node 6), - 68(1) epipterygoid con- bularis caudalis never enclosed by prearticular (oc- tacts palatine when present (occurs also at node curs also at nodes 2 and 19 and in indica). leithii: 9), - 73(2) epipterygoid fuses to pterygoid in adults - 14(2) eight or nine neurals (occurs also at nodes only (occurs also in bibroni, frenatum, gangeticus, 2 and 13 and in bibroni and muticus), - 70(0) muticus, subplanus, and triunguis), - 76(2) qua- when epipterygoid is present, pterygoid contacts 1987 MEYLAN: TRIONYCHIDAE 83

Fig. 33 (continued). curs at nodes 3 and 8 and in formosus), - 71(3) foramen nervi trigemini between epipterygoid and epipterygoid always contacts prootic anterior to quadrate or not at all (occurs also at nodes 7 and foramen nervi trigemini (occurs also in indica), - 17). nigricans: - 60(2) foramen posterius canalis 76(1) quadratojugal not participating in processus carotici interni occurs within lateral crest of basi- trochlearis oticum (a unique reversal). subplanus: occipital tubercle (occurs also at node 7), - 68(3) - 14(1) nine neurals present (a unique reversal), when present epipterygoid does not contact pal- - 16(0) no pleurals meeting at midline, - 64(2) atine (occurs also at nodes 4 and 8 and in sene- basisphenoid occasionally medially constricted (a galensis), - 78(2) 22.1% or more of processus unique reversal), - 73(2) epipterygoid fuses to trochlearis oticum made up by parietal (occurs pterygoid in adults only (occurs also in bibroni, also at node 17 and in elegans). hurum: - 34(2) elegans, frenatum, gangeticus, muticus, and triun- jugal contacts parietal in one-half of sample (oc- guis), - 90(3) eight ossifications in corpus hyoidis curs also at nodes 2 and 15 and in muticus), - (occurs also at nodes 7 and 18 and in hurum), - 71(2) epipterygoid contacts prootic anterior to fo- 95(2) symphyseal ridge present and in a depression ramen nervi trigemini in about one-half of sample (occurs after loss at node 14). triunguis: 73(2) epi- (occurs also at node 7), -90(3) eight ossifications pterygoid fuses to pterygoid in adults only (occurs in corpus hyoidis (occurs also at nodes 7 and 18 also in bibroni, elegans,frenatum, gangeticus, mu- and in subplanus), - 91(1) only one ossification ticus, and subplanus). euphraticus: - 46(1) basi- in second branchial horn (a unique reversal). gan- sphenoid fails to reach palatines (unique among geticus: - 41(2) dorsolateral edge of apertura nar- trionychids), - 64(2) basisphenoid occasionally ium externum weakly emarginate (a reversal that medially constricted (a reappearance after loss at occurs also at node 19), - 73(2) epipterygoid fuses node 17). swinhoei: - 32(2) jugal contacts squa- to pterygoid in adults only (occurs also in bibroni, mosal in one-half of sample (occurs also in for- elegans, frenatum, muticus, subplanus, and triun- mosus, leithii, nigricans, muticus, and sinensis), - guis), - 91(3) seven or more ossifications in sec- 54(2) foramen palatinum posterius forms in pal- ond branchial horn (occurs also at node 18). si- atine only (occurs also at node 2 and in sinensis). nensis: - 9(1) seven plastral callosities present in ferox: - 1(2) hyoplastra and hypoplastra fuse in plastron (a reversal that occurs also at node 21), adults. spiniferus: - 64(2) basisphenoid occasion- - 15(3) position of neural reversal highly variable ally medially constricted. muticus: - 1(4) nuchal with more than one reversal sometimes present bone more than four times wider than long (occurs (occurs also at node 20), - 17(4) posteriormost also at node 15), - 14(2) eight or nine neurals neural reversal present at neural six or anterior (occurs also at nodes 2 and 13 and in bibroni and (occurs also at node 20), - 32(2) jugal contacts leithi), - 32(2) jugal contacts squamosal in one- squamosal in one-half of sample (occurs also in half of sample (occurs also in formosus, leithii, formosus, leithii, nigricans, muticus, and swin- nigricans, muticus, and swinhoei), - 34(2) jugal hoez), - 54(2) foramen palatinum posterius forms contacts parietal on skull surface in one-half of in palatine only (occurs also at node 2 and in swin- sample (occurs also at node 2 and 15 and in hu- hoei). steindachneri: - 1(2) nuchal between two rum), - 49(2) vomer fails to reach intermaxillary and three times wider than long (a reversal that foramen (a unique reversal), - 73(2) epipterygoid occurs elsewhere in formosus), - 15(1) position fuses to pterygoid in adults only (occurs also in of neural reversal is always at the same neural (a bibroni, elegans, frenatum, gangeticus, subplanus, reversal that occurs also at node 17), - 34(3) jugal and triunguis), - 91(2) two or more ossifications always contacts parietal on skull surface (also oc- in second branchial horn of hyoid. 84 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 186

Fig. 34. The second oftwo most parsimonious most trionychids, carettochelyids, and staurotyp- cladograms of the living Trionychidae. Characters ine kinosternids), - 109(2) metischial processes supporting the nodes are as follows: Node 1: The not well developed (occurs also at node 1 1). Node evidence for monophyly of the Trionychidae is 3: - 5(4) no peripheral elements (occurs also at summarized in table 21. Node 2: - 10(2) hyoplas- node 6), - 34(3) jugal always contacts parietal on tra and hypoplastra fuse just after hatching, - skull surface (occurs also informosus, indica, and 13(2) hypoplastra are lateral to xiphiplastra at hypo- steindachneri), - 36(2) vomer not in contact with xiphiplastral union, - 14(2) eight or nine neurals prefrontal (occurs also in indica and reverses in (reduced from always nine) (occurs also at node elegans), - 53(3) foramina palatinum posterius 19 and in indica and leithii), - 16(2) eighth pleu- small and divided, - 69(2) no contact between rals only or seventh and eighth pleurals meet on pterygoid and foramen nervi trigemini when epi- midline (occurs also at nodes 10 and 17), - 17(1) pterygoid is present (occurs also in muticus and neural reversal always occurs at neural eight (may steindachneri), - 72(2) epipterygoid contacts be primitive condition), - 54(2) foramen palati- prootic posterior to foramen nervi trigemini, - num posterius forms in palatine only (occurs also 100(2) ilia curve medially, - 113(1) coracoid in sinensis and swinhoet), - 58(2) foramen jug- shorter than either process of scapula (unique ulare posterius excluded from fenestra postotica among trionychids). Node 4: - 19(2) epiplastra by pterygoid arching to contact opisthotic, - 68(2) I-shaped (occurs also in punctata), - 25(2) cara- epipterygoid excluded from contact with palatine pace straight or concave posterolaterally (occurs in 50 percent of cases where it is present (occurs also in punctata), - 53(4) posterior palatine fo- also at node 8), - 93(2) basihyals in close contact ramen consists of many small foramina, - 88(2) and projecting anteriorly, - 98(2) foramen inter- strong dorsal processes on cervicals (occurs also mandibularis caudalis never enclosed by preartic- at node 9). Node 5: - 2(2) anterior and posterior ular (occurs also at node 12 and in indica and costiform processes united (occurs also at node 6), formosus), - 107(1) ischia extend into thyroid - 3(2) anterior edge of first body vertebra is in fenestra (reversal of a derived condition shared by the middle ofthe nuchal bone (occurs also at node 1 987 MEYLAN: TRIONYCHIDAE 85

Fig. 34 (continued). cervicals (occurs also at node 4), - 92(2) ossifi- 6 and in aubryi), - 107(2) no extension of ischia cations ofsecond branchial horn broad and strong- into thyroid fenestra (occurs also at node 6), - ly sutured, - 112(2) angle of acromion process to 112(2) angle of acromion process to scapula ap- scapula approaches that of coracoid to acromion. proaches that ofcoracoid to acromion (occurs also Node 10: - 14(3) eight or fewer neurals (fused one at nodes 9 and 14). Node 6: - 1(3) nuchal at least and two counted as two), - 16(2) seventh and three times wider than long (occurs also in sene- eighth pleurals meet in some individuals (occurs galensis), - 2(2) anterior and posterior costiform also at node 2 and at node 17), - 41(3) dorsal processes united (occurs also at node 5), - 3(2) edge of apertura narium externum strongly emar- anterior edge of first body vertebra in the middle ginate (occurs also at node 18), - 78(2) parietal ofthe nuchal (occurs also at node 5 and in aubryi), makes up 22.1 percent or more of processus troch- - 5(4) no peripheral bones (occurs also at node learis oticum (occurs also in elegans and ni- 3), - 9(3) four plastral callosities (reversal to 5 gricans). Node 11: - 8(2) eighth pleurals reduced occurs at node 16 and in cartilagineus), - 17(3) or absent, - 48(1) vomer divides maxillae (occurs orientation of neural series reverses at neural six also at node 9 and in senegalensis), - 49(1) vomer or seven or anterior to that point, - 21(2) depres- reaches foramen intermaxillaris (occurs also at node sions for ilia in eighth pleural absent (occurs also 9, in senegalensis and punctata), - 74(2) inter- in elegans), - 23(2) bridge short (occurs also in maxillary foramen about 60% oflength of primary elegans), - 41(2) dorsal edge of apertura narium palate, - 91(3) seven or more ossifications in sec- externum weakly emarginate (occurs also in aubryi ond branchial horn (also occurs in gangeticus), - and senegalensis), - 73(3) epipterygoid never fus- 109(2) no distinct metischial processes (occurs also es to pterygoid, - 91(2) two or more ossifications at node 2). Node 12: - 9(4) only two callosities in second branchial horn of hyoid, - 107(2) no on plastron (occurs also in elegans), - 41(2) dorsal extension of ischia into thyroid fenestra (occurs edge of apertura narium externum weakly emar- also at node 5). Node 7: - 4(2) first and second ginate (a unique reversal to a condition widespread neurals fuse (occurs also at node 20), - 34(1)jugal in the trionychinae), - 98(2) foramen interman- never contacts parietal on skull surface (a reversal), dibularis caudalis never enclosed by prearticular - 70(0) when epipterygoid is present, pterygoid (occurs also at node 2, in formosus and indica). contacts foramen nervi trigemini between epi- Node 13: - 15(3) location ofneural reversals high- pterygoid and quadrate or not at all, - 76(2) qua- ly variable (occurs also in sinensis), - 17(4) pos- dratojugal participates in processus trochlearis oti- teriormost reversal occurs at neural six (occurs cum (occurs also in elegans, frenatum, gangeticus, also in sinensis), - 29(2) sexual dimorphism in and sinensis), - 90(3) eight ossifications in corpus disc length (occurs also in indica). Node 14: - 9(1) hyoideum. Node 8: - 60(2) foramen posterius seven plastral callosities (a reversal to most prim- canalis carotici interni lies within ridges which ex- itive condition which occurs also in sinensis),- tend laterally from the basioccipital tubercles (oc- 24(2) largest adult size about 200 mm or less disc curs also in nigricans), - 68(2) when present, epi- length (occurs also at node 20), - 69(2) contact pterygoid fails to contact palatine in 50 percent or between pterygoid and foramen nervi trigemini more of sample (occurs also at node 2 and in ni- does not occur when epipterygoid is present (oc- gricans), -7 1(2) epipterygoid contacts prootic an- curs also at node 3 and in steindachneri), - 75(2) terior to foramen nervi trigemini in 50 percent or postorbital bar very narrow, less than one-fifth more of sample (occurs also in hurum and stein- orbit diameter (occurs also at node 21), - 90(2) dachneri), - 87(2) a ventral keel present on pos- six ossifications in corpus hyoidis (a reversal that terior end of 8th cervical (occurs also in euphra- occurs also in triunguis), - 109(1) metischial pro- ticus). Node 9: - 34(3) jugal always contacts cesses present and distinct (a unique reversal), - parietal on skull surface (also occurs at node 3 in 112(2) angle of acromion process to scapula ap- formosus and steindachneri), - 41(1) no dorsal proaches that of coracoid to acromion (occurs also emargination of apertura narium extemum (a at nodes 5 and 9). Node 15: - 32(2)jugal contacts unique reversal), - 48(1) vomer divides maxillae squamosal in about one-halfofsample (occurs also (occurs also at node 11 and in senegalensis), - in euphraticus, muticus, and sinensis), - 64(3) ba- 49(1) vomer reaches intermaxillary foramen (oc- sisphenoid almost always medially constricted, - curs also at node 1 1, in punctata and in senegalen- 95(2) symphyseal ridge strong and in a depression sis), - 68(3) when present, epipterygoid never (occurs also in cartilagineus). Node 16: - 9(2) five contacts palatine (occurs also in frenatum, ni- callosities present in plastron (a reversal that oc- gricans, and senegalensis), - 76(1) no contribu- curs also in cartilagineus), - 20(2) anterior pro- tion by quadratojugal to processus trochlearis oti- cesses of epiplastra of intermediate length. Node cum (a reversal that occurs elsewhere in 17: - 16(2) seventh and eighth pleurals meet on steindachneri), - 88(2) strong dorsal processes on midline in some individuals (occurs also at nodes 86 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 186

Fig. 34 (continued). - 41(2) dorsal edge of apertura narium externum 2 and 10). Node 18: - 15(2) neural reversal occurs weakly emarginate laterally (occurs also at node 6 at adjacent neurals, - 32(1) jugal never contacts and in aubryi), - 48(1) vomer divides maxillae squamosal (a unique reversal). Node 19: - 14(2) (occurs also at nodes 9 and 11), - 49(1) vomer some individuals with eight neurals (fused first and reaches intermaxillary foramen (occurs also at second neurals counted as two, occurs also at node nodes 9 and 11 and in punctata), - 68(3) when 2, and in bibroni), - 76(2) quadratojugal partic- present, epipterygoid never contacts palatine. ipates in processus trochlearis oticum (occurs also punctata: - 7(2) prenuchal bone present (occurs at node 7, and in elegans andfrenatum). Node 20: also in senegalensis), - 12(2) xiphiplastra fuse in - 1(4) nuchal bone four or more times wider than some individuals (occurs also in some aubryi), - long (occurs also in muticus), - 4(2) first and sec- 14(4) some individuals with seven neurals in con- ond neurals fused (occurs also at node 7), - 20(3) tinuous series, - 19(2) epiplastra I-shaped (occurs anterior processes of epiplastra long (occurs also also at node 4), - 25(2) carapace straight or con- in cartilagineus), - 24(2) largest adult size about cave laterally (occurs also at node 4), - 49(1) vo- 200 mm disc length (occurs also at node 14), - mer reaches intermaxillary foramen (occurs also 59(2) foramen jugulare posterius excluded from at nodes 9 and 11 and in senegalensis). bibroni: - fenestra postotica by descending process of opis- 14(2) some individuals with eight (rather than nine) thotic which usually reaches pterygoid, - 70(2) neurals (occurs also at nodes 2 and 19 and in lei- when epipterygoid is present pterygoid contacts thi), - 73(2) epipterygoid fuses to pterygoid in foramen nervi trigemini between epipterygoid and adults only (occurs also in frenatum, elegans, parietal or not at all. Node 21: - 9(3) four plastral triunguis, muticus, gangeticus, and subplanus). in- callosities (a reversal to the common condition in dica: - 3(3) anterior edge of first body vertebra trionychines), - 17(2) posteriormost neural re- at anterior edge of nuchal bone, - 29(2) sexual versal occurs at neural seven or anterior to it (a dimorphism in disc length (occurs also at node reversal that occurs also in cartilagineus andfor- 13), - 36(2) vomer fails to contact prefrontal (oc- mosus), - 75(2) postorbital bar less than one-fifth curs also at node 3), - 65(3) premaxilla usually of orbit diameter (occurs also at node 14). Specific absent (occurs also in aubryi), - 71(3) epiptery- characters. aubryi: - 3(2) anterior edge of first goid always contacts prootic anterior to foramen body vertebra at middle of nuchal bone (occurs nervi trigemini (occurs also in steindachneri), - also at nodes 5 and 6), - 12(2) xiphiplastra fuse 74(0) intermaxillary foramen quite reduced, av- in some individuals (occurs also in some puncta- eraging 7% of primary palate, - 75(0) postorbital ta), - 41(2) dorsal edge of apertura narium ex- bar about two times orbit diameter, - 98(2) fo- ternum weakly emarginate (occurs also at node 6 ramen intermandibularis caudalis never enclosed and in senegalensis), - 65(2) premaxillae usually by prearticular (occurs also at nodes 12 and in absent. frenatum: - 68(3) epipterygoid, when formosus). cartilagineus: - 9(2) five plastral cal- present, never contacts palatine (occurs also at node losities (a reversal that occurs also at node 18), - 9, in nigricans and in senegalensis), - 73(2) epi- 17(2) posteriormost neural reversal occurs at neu- pterygoid fuses to pterygoid in adults only (occurs ral seven (a character reversal that occurs also at also in elegans, bibroni, triunguis, muticus, gan- node 21 and in formosus), - 20(3) anterior epi- geticus, and subplanus). elegans: - 9(4) only two plastral process long (occurs also at node 20), - plastral callosities (occurs also at node 12), - 21(2) 64(2) basisphenoid occasionally medially con- depressions on eighth pleurals for contact of ilia stricted (occurs also in euphraticus and spiniferus), absent (occurs also at node 6), - 23(2) bridge short - 95(2) strong symphyseal ridge present (occurs (occurs also at node 6), - 36(1) vomer contacts also at node 15). triunguis: - 73(2) epipterygoid prefrontal (a unique reversal), - 42(2) dorsal edge fuses to pterygoid in adults only (occurs also in of apertura narium externum medially emargin- bibroni,frenatum, elegans, muticus, gangeticus, and ate, - 68(1) when present, epipterygoid always subplanus), - 90(2) six ossifications in corpus contacts palatine (a unique reversal), - 73(2) epi- hyoidis (a reversal that occurs also at node 14). pterygoid fuses to pterygoid in adults only (occurs euphraticus: - 64(2) basisphenoid occasionally also in frenatum, bibroni, triunguis, muticus, gan- medially constricted (occurs also in cartilagineus geticus, and subplanus), - 100(1) ilia do not curve and spiniferus), - 87(2) ventral keel present on medially (a unique reversal). senegalensis: - 1(3) posterior end ofeighth cervical (occurs also at node nuchal three times wider than long (occurs also at 8). swinhoei:- 32(2) jugal contacts squamosal in node 6), - 7(2) prenuchal bone present (occurs one-half of sample (occurs also at node 15 and in also in punctata), - 9(0) nine or more plastral muticus and sinensis), - 54(2) foramen palatinum callosities (includes gular pair), - 14(5) seven or posterius forms in palatine only (occurs also at fewer neurals, - 16(4) pleural bones, in addition node 2). ferox: - 1(2) hyo- and hypoplastra fuse to pairs six, seven, and eight, meet at the midline, in adults. spiniferus: - 64(2) basisphenoid me- 1 987 MEYLAN: TRIONYCHIDAE 87

Fig. 34 (continued). pus hyoidis (occurs also at node 7 and in subpla- dially constricted on occasion (occurs also in car- nus), - 91(1) a single ossification in the second tilagineus, euphraticus and subplanus). muticus: - horn of hyoid (a unique reversal). gangeticus: - 1(4) nuchal bone four or more times wider than 34(1) jugal never contacts parietal on skull surface long (occurs also at node 20), - 32(2) jugal con- (a reversal that occurs at node 7 and in nigricans), tacts squamosal in one-half of sample (occurs also - 73(2) epipterygoid fuses to pterygoid in adults at node 15 and in swinhoei and sinensis), - 34(2) only (occurs also in bibroni, frenatum, elegans, jugal contacts parietal on skull surface in one-half muticus, triunguis, and subplanus), - 91(3) seven ofsample (unique occurrence after reversal at node or more ossifications in second branchial horn of - 7), - 73(2) epipterygoid fuses to pterygoid in adults hyoid (occurs also at node 11). sinensis: 9(1) only (occurs also in bibroni, frenatum, elegans, seven callosities in plastron (a reversal that occurs gangeticus, subplanus, and triunguis), - 91(2) be- also at node 14), - 15(3) high variability of point tween two and six ossifications in second branchial of posteriormost neural reversal (occurs also at horn of hyoid (a unique reversal). formosus: - node 13), - 17(4) posteriormost neural reversal 1(2) nuchal bone only two times wider than long occurs at or anterior to neural six (occurs also at - (a reversal that occurs also in steindachneri), - node 13), 32(2)jugal contacts squamosal in one- 17(2) last reversal in neural orientation occurs at half of sample (occurs also at node 15 and in mu- neural seven (a character reversal that occurs also ticus and swinhoei), - 54(2) foramen palatinum at node 21 and in cartilagineus), - 34(3) jugal posterius forms in palatine only (occurs also at always contacts parietal on skull surface (also oc- node 2), - 95(1) symphyseal ridge absent (a re- curs at nodes 3 and 9 and in steindachneri), - versal that occurs also in steindachneri). stein- 98(2) foramen intermandibularis caudalis never dachneri: - 1(2) nuchal bone only two times wider enclosed by prearticular (occurs also at nodes 12 than long (a reversal that occurs also informosus), and in indica). leithii: - 14(2) some individuals - 15(l) neural reversal always occurs at the same with eight neurals (occurs also at nodes 2 and 19 neural (a unique reversal), - 34(3) jugal always and in bibroni), - 70(0) when epipterygoid is pres- contacts parietal on skull surface (also occurs at ent pterygoid contacts foramen nervi trigemini be- nodes 3 and 9 and informosus), - 71(3) epipter- tween epipterygoid and quadrate or not at all (oc- ygoid contacts prootic anterior to foramen nervi - curs also at node 7). nigricans: - 34(1)jugal never trigemini (occurs also in indica), 76(1) qua- contacts parietal on skull surface (a reversal that dratojugal excluded from processus trochlearis oti- occurs at node 7 and in gangeticus), - 60(2) fo- cum (a reversal that occurs also at node 9), -9 5 (1) ramen posterius canalis carotici interni located symphyseal ridge absent (a reversal that occurs within a lateral crest of the basioccipital tubercle also in sinensis). subplanus: - 14(1) nine neurals - (occurs also at node 8), - 68(3) epipterygoid does present (a unique reversal), 16(0) no pleurals not contact palatine (occurs also at node 9 and in meet on midline, - 64(2) basisphenoid medially frenatum and senegalensis), - 78(2) parietal makes constricted on occasion (occurs also in cartilagi- up 22. 1% or more ofprocessus trochlearis oticum. neus, euphraticus, and spiniferus), - 73(2) epi- hurum: - 41(3) dorsal edge of apertura narium pterygoid fuses to pterygoid in adults only (occurs externum strongly emarginate laterally (occurs also also in bibroni, frenatum, elegans, muticus, triun- - at nodes 10 and 20), - 71(2) epipterygoid contacts guis, and gangeticus), 90(3) eight ossifications prootic anterior to foramen nervi trigemini in one- in corpus hyoidis (occurs also at node 7 and in half of sample, - 90(3) eight ossifications in cor- hurum). 88 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 186

CLASSIFICATION OF THE LIVING TRIONYCHIDAE

TRIONYCHIDAE TRIBE CYCLANORBINI (FITZINGER, 1826; AS TRIONYCHOIDEA) (HUMMEL, 1929; AS CYCLANORBINAE) BELL, 1828 NEW RANK

TYPE GENus: Trionyx Geoffroy, 1809. TYPE GENUS: Cyclanorbis Gray, 1854. DIAGNoSIs: Members ofthe Trionychoidea DiAGNosIs: Members of Cyclanorbinae (sensu Gaffiey, 1975, 1984) with 18 or fewer having no peripheral elements, medially peripherals, no pygal or suprapygal, a boo- curving ilia, coracoid shorter than either pro- merang-shaped entoplastron, quadratojugal cess of scapula, jugal always in contact with not contacting postorbital, jugal contacting parietal on dorsal surface of skull, vomer not parietal, premaxillae fused and excluded from in contact with prefrontal (except in Cycla- apertura narium externum by maxillae, hy- norbis elegans), foramen palatinum posterius perphalangy ofmanus digits four and five and small and divided, no contact between pter- pes digit four, three clawed digits in manus ygoid and foramen nervi trigemini when and pes, cervical centra all opisthocoelous epipterygoid is present, and epipterygoid- except eighth which lacks central articulation prootic contact posterior to foramen nervi to first thoracic vertebra, no ventral process trigemini. of eighth cervical vertebra, corpus hyoidis CoNTENr: The four living species of this composed of six or eight ossifications, ilia tribe belong to two genera, Cyclanorbis and curve posteriorly, pectineal processes lie in a Cycloderma. single plane and are in broad contact with plastron, and pectineal processes equal to or wider than interpubic contact. Cyclanorbis Gray, 1854 CONTENT: Twenty-two living species di- TYPE SPECIES: Cyclanorbis senegalensis vided among two subfamilies (the Cycla- (Dumeril and Bibron, 1835). norbinae and Trionychinae) and about 220 DIAGNosIs: Cyclanorbine trionychids, with named fossil species, some of which are, on the anterior and posterior costiform process- occasion, placed in a third subfamily, the es united, no extension of ischia into thyroid Plastomeninae. fenestra, angle between acromion process and body of scapula approaching that of acro- SUBFAMILY CYCLANORBINAE mion to coracoid, and a variable tendency of HUMMEL, 1929 pleurals to divide the neural series by meeting TYPE GENUS: Cyclanorbis Gray, 1854. on the midline. DLAGNOsIs: Trionychid turtles in which the CONTENT: Two species, Cyclanorbis sene- hyo- and hypoplastra fuse just after hatching, galensis and Cyclanorbis elegans. the hypoplastra are lateral to the xiphiplastra at the hypoxiphiplastral union, the basihyals Cyclanorbis senegalensis of the corpus hyoidis are in close contact and project anteriorly, the foramen intermandib- (Dumeril and Bibron, 1835) ularis caudalis is never enclosed by the prear- DiAGNosIS: A species of Cyclanorbis with ticular, metischial processes are not well de- a prenuchal bone present, nine or more plas- veloped, foramen palatinum posterius forms tral callosities, seven or fewer neural bones, within the palatine, and the foramen jugulare pleural bones in addition to numbers six, sev- postenus is isolated from the fenestra post- en, and eight meeting on the midline, vomer otica by dorsal arch of the pterygoid. dividing maxillae and reaching intermaxil- CONTENT: Considered to include five living lary foramen, and epipterygoid never con- species here divided into two tribes. tacting palatine. 1987 MEYLAN: TRIONYCHIDAE 89

Cyclanorbis elegans (Gray, 1869) terolaterally concave carapacial margin and in which the xiphiplastra suture and fuse on DiAGNOSIS: A species of Cyclanorbis with the midline in large adults and the vomer only two plastral callosities, no depressions reaches the intermaxillary foramen dorsal to on the eighth pleurals for articulation of ilia, the maxillae. Members of this tribe differ fur- a short bridge, the vomer in contact with the ther from all other known trionychids by the prefrontals; when present, epipterygoid al- primitive retention of peripheral elements. ways in contact with palatine, and apertura CONTENT: One genus Lissemys here con- narium externum medially emarginate. sidered to include a single species Lissemys Cycloderma Peters, 1854 punctata. TYPE SPECIES: Cycloderma frenatum Pe- Lissemys Malcolm Smith, 1931 ters, 1854. TYPE SPECIES: Lissemys punctata (La- DIAGNOSIS: Members of Cyclanorbini in cepede, 1788). which the epiplastra are I-shaped rather than DIAGNOSIS: As for the tribe Lissemydini. J-shaped, the margin of the carapace is con- CONTENT: As for the tribe Lissemydini. cave posterolaterally, the middle cervicals (4, 5, and 6) possess well-developed dorsal pro- Lissemys punctata (Lacepede, 1788) cesses, and the posterior palatine foramina consist of numerous very small openings DiAGNOSIS: As for the tribe Lissemydini. barely distinguishable from the nutritive foramina of the palate. SUBFAMILY TRIONYCHINAE CONTENT: Two living species, Cycloderma (FITZINGER, 1826; AS TRIONYCHOIDEA) frenatum and Cycloderma aubryi. LYDEKKER, 1889 TYPE GENus: Trionyx Geoffroy, 1809. Cycloderma frenatum Peters, 1854 DLAGNOSIS: Trionychid turtles with the nu- DIAGNOSIS: Members of Cycloderma in chal bone at least three times wider than long, which the epipterygoid, when present, never anterior and posterior costiform processes contacts the palatine and fuses to the ptery- united, no peripheral bones, neural series al- goid in large adults, and in which the vomer ways containing at least one reversal ofneural is absent. orientation, depressions for articulation of ilia This species differs further from its living absent from eighth pleural, a short bridge, congener in retaining primitive features in- two or more ossifications in the second bran- cluding the total absence of midline suturing chial horn (except in some hurum), dorsal or fusion of the xiphiplastra and in always edge of apertura narium externum slightly to retaining the premaxillae. strongly emarginate, and epipterygoid typically fusing to pterygoid in adults. Cycloderma aubryi (A. Dumeril, 1856) CONTENT: This study suggests that the subfamily Trionychinae consists of four DIAGNOSIS: Members of Cycloderma in monophyletic species groups. However, the which the xiphiplastra suture and fuse on the relationships between the four groups is not midline in large adults, the dorsal edge of the totally resolved. To reflect this lack of reso- apertura narium externum is weakly emar- lution the recognition of four tribes is rec- ginate, and premaxillae are usually absent. ommended below. By failing to designate groups between the rank of subfamily and TRIBE LISSEMYDINI tribe, the uncertainty about the interrelation- (WILLIAMS, 1950; AS LISSEMYDINAE) ships of these tribes can be indicated. In the NEW RANK interest of maintaining as much nomencla- TYPE GENuS: Lissemys Malcolm Smith, torial stability as possible, the use of four 1931. tribes at this level is thought to be preferable DIAGNOSIS: Cyclanorbine trionychids with to the recognition of four genera. The four a prenuchal bone, I-shaped epiplastra, pos- tribes constituting the Trionychinae are the 90 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 186

Chitrini, Aspideretini, Trionychini, and ally absent, and sexual dimorphism may exist Pelodiscini. (Wirot, 1979). CONTENT: The only living form is Chitra TRIBE CHITRINI indica. (GRAY, 1870; AS CHITRADAE) NEW RANK Chitra indica (Gray, 1831) TYPE GENUS: Chitra Gray, 1844. DiAGNOSIS: As for the genus. DIAGNOSIS: Trionychine trionychids in which the foramen posterius canalis carotici interni lies within a ridge extending laterally Pelochelys Gray, 1864 from the basioccipital tubercle, the eighth TYPE SPECIES: Pelochelys bibroni (Owen, cervical has a small ventral keel, and the 1853). epipterygoid usually does not contact the pal- DiAGNOSIS: Members of the subtribe Chi- atine but usually does contact the prootic an- trina which sometimes have eight neurals terior to the foramen nervi trigemini. (rather than nine, with fused one and two CONTENT: In the interest of nomenclatorial counted as two), vomer often contacts basi- stability this tribe is herein considered to be sphenoid, and the epipterygoids fuse to the composed of three monotypic genera in two pterygoid in adults. subtribes: Chitra indica, Pelochelys bibroni, Pelochelys differs further from its living sis- and Amyda cartilaginea. ter taxon, Chitra indica, in retaining primitive features including: prezygapophyses of SUBTRIBE CHITRINA the first thoracic vertebra recessed below the (GRAY, 1870; AS CHITRADAE) nuchal, foramen intermandibularis caudalis NEW RANK sometimes enclosed by prearticular, inter- TYPE GENUS: Chitra Gray, 1844. maxillary foramen larger (about 37% of pri- DiAGNOSIS: Members of the tribe Chitrini mary palate), postorbital bar two-thirds of with strong dorsal processes on cervicals four, the width of the orbit, premaxillary usually five, and six, ossifications ofthe second bran- present, and sexual dimorphism unknown. chial horn of the hyoid composed of three wide elements which are strongly sutured to SUBTRIBE AMYDINA one another, jugal always in contact with pa- (LOVERIDGE, 1942; AS AMYDIDAE) rietal on skull surface, no dorsal emargination NEW RANK of apertura narium extemum, and vomer dividing maxillae and reaching intermaxillary TYPE GENuS: Amyda Geoffroy, 1809. foramen. DIAGNOSIS: Members of the tribe Chitrini CONTENT: Contains Pelochelys bibroni and with five plastral callosities, elongate anterior Chitra indica and is used to suggest that they projections of epiplastra, a long symphysis share a common ancestor not shared by Amy- with a strong symphyseal ridge, and frequent- da cartilaginea. ly a medially constricted basisphenoid. CONTENT: The only living member is Amy- Chitra Gray, 1844 da cartilaginea. TYPE SPECIES: Chitra indica (Gray, 1831). DIAGNoSIs: Members of the subtribe Chi- Amyda Geoffroy, 1809 trina in which the anterior edge of the pre- TYPE SPECIES: Amyda cartilaginea (Bod- zygapophysis ofthe first thoracic vertebra lies daert, 1770). at the anterior edge of the carapace, the fo- DIAGNOSIS: As for the subtribe Amydina. ramen intermandibularis caudalis is never enclosed by the prearticular, the intermaxil- CONTENT: As for the subtribe Amydina. lary foramen is quite reduced (about 7% of primary palate), the postorbital bar is two Amyda cartilaginea (Boddaert, 1770) times orbit diameter, the premaxillary is usu- DIAGNOSIS: As for the subtribe Amydina. 1 987 MEYLAN: TRIONYCHIDAE 91

TRIBE TRIONYCHINI intermaxillary foramen is about 60 percent (FITZINGER, 1826; AS TRIONYCHOIDEA) of primary palate in length, there is no NEW RANK distinct metischial process (except in spinif- TYPE GENUS: Trionyx Geoffroy, 1809. erus and muticus), and the vomer divides the DIAGNOSIS: Members of the subfamily maxillae and reaches the intermaxillary fo- Trionychinae with eight or fewer neurals ramen. (fused first and second count as two), parietal CONTENT: The relationships of the mem- makes up nearly one-quarter of processus bers of this subtribe can be completely por- trochlearis oticum, and dorsal margin of trayed by the use of two generic names, Ra- apertura narium extemum is strongly emar- fetus and Apalone, with two subgenera ginate (except in swinhoei and euphraticus). (Platypeltis and Apalone) constituting the lat- CONTENT: Considered to include six living ter. species: triunguis, euphraticus, swinhoei, fe- Rafetus Gray, 1864 rox, spiniferus, and muticus. The relationships within this tribe, as understood from TYPE SPECIES: Rafetus euphraticus (Dau- the current analysis, can best be portrayed din, 1802). through the use of two subtribes, three gen- DiAGNOSIS: Members of the subtribe Apa- era, and two subgenera. lonina with only two callosities in the plastron, the foramen intermandibularis caudalis never enclosed by the prearticular, and the SUBTRIBE TRIONYCHINA dorsal edge of the apertura narium externum (FITZINGER, 1826; AS TRIONYCHOIDEA) only weakly emarginate. NEW RANK CONTENT: Two living species, euphraticus TYPE GENUS: Trionyx Geoffroy, 1809. and swinhoei. DIAGNOSIS: Members of Trionychini with six ossifications in the corpus hyoidis, epi- Rafetus euphraticus (Daudin, 1802) pterygoid fusing to the pterygoid in very large adults, and exoccipital partly or completely DiAGNOSIS: Members of the genus Rafetus isolated from the pterygoid by the basioccip- with a ventral keel present on the eighth cer- ital. Differing further from members of the vical vertebra, the basisphenoid medially sister subtribe in its primitive retention of constricted in some individuals, and the ba- complete eighth pleurals and a smaller inter- sisphenoid failing to contact the palatines. maxillary foramen (about one-third primary palate). Rafetus swinhoei (Gray, 1873) CONTENT: One species, Trionyx triunguis. DIAGNOSIS: Members of the genus Rafetus in which the jugal contacts the squamosal, Genus Trionyx Geoffroy, 1809 the foramen palatinum posterius is surround- TYPE SPECIES: Trionyx triunguis (Forskal, ed by the palatine, and the basisphenoid con- 1775). tacts the palatines. DIAGNOSIS: As for subtribe Trionychina. 1832 CONTENT: As for subtribe Trionychina. Apalone Rafinesque, TYPE SPECIES: Apalone spiniferus (Le Sueur, Trionyx triunguis (Forsklil, 1775) 1827). DiAGNOSIS: Members of the subtribe Apa- DIAGNOSIS: As for subtribe Trionychina. lonina in which the location of the posteriormost neural reversal is highly variable but SUBTRIBE APALONINA NEW NAME occurs at or anterior to neural six and in which TYPE GENUS: Apalone Rafinesque, 1832. there is marked sexual dimorphism. DIAGNOSIS: Members of the Tribe Trion- CONTENT: Two subgenera, Apalone and ychini in which the eighth pair of pleurals is Platypeltis are used within this genus to re- reduced or absent, there are seven or more flect the relationship of the three included ossifications in the second branchial horn, the species. 92 BULLETIN AMERICAN MUSSE'1UM OF NATURAL HISTORY VOL. 186

Apalone (Apalone) spinifera members of the sister taxon (subgenus Apa- (Le Sueur, 1827) lone) by the fusion of the hyo-hypoplastra DIAGNOSIS: Members of the genus Apalone which occurs in nearly all adults. This species that can be distinguished from congeners be- is further diagnosable by only four callosities longing to the subgenus Platypeltis by the in the plastron of all adult individuals, eight presence of seven plastral callosities in old ossifications in the adult corpus hyoidis, ab- adult males, small adult size (200 mm or less sence of metischial processes, wider acro- disc length), six ossifications in corpus hyoi- mion to scapula angle, and large adult size. dis, postorbital bar about one-fifth orbit diameter, metischial process distinct, angle of TRIBE ASPIDERETINI, NEW NAME acromion to scapula approaches that of coracoid to acromion, and contact between pter- TYPE GENUS: Aspideretes Hay, 1904. ygoid and foramen nervi trigemini does not DIAGNosIs: Trionychine turtles with the occur when epipterygoid is present. This basisphenoid medially constricted, a strong species can be distinguished from its sister symphyseal ridge in a depression, the quad- taxon, Apalone (Apalone) muticus, by its rate excluded from the foramen nervi trigem- higher number of ossifications in the second ini by contact of the pterygoid and prootic branchial horn (seven or more), its medially posterior to this structure (except in A. lei- constricted basisphenoid (occurs only in some thui), and jugal contacting squamosal in some individuals), and by relatively primitive con- individuals. ditions for nuchal shape (about three times CONTENT: Here considered to include two wider than long) and jugal contacts (never genera, Aspideretes and Nilssonia. contacts parietal on skull surface). Aspideretes Hay, 1904 Apalone (Apalone) mutica TYPE SPECIES: Aspideretes gangeticus (Cu- Le Sueur, 1827 vier, 1825). DiAGNosIs: Members of the genus Apalone DIAGNOSIS: Members of Aspideritini most that can be distinguished from congeners be- easily recognized by two pairs of neurals be- longing to the subgenus Platypeltis by the tween the first pair of pleurals, five callosities presence of seven plastral callosities in old in the plastron, and anterior epiplastral pro- adult males, small adult size (200 mm or less jections of intermediate length. disc length), six ossifications in corpus hyoi- CONTENT: The interrelationships ofthe four dis, postorbital bar about one-fifth of orbit living species in this genus is not fully re- diameter, metischial processes distinct, angle solved. To reflect this no superspecific ranks of acromion to scapula approaches that of are used within the genus. The genus contains coracoid to acromion, and contact between four living species: gangeticus, hurum, leithii, pterygoid and foramen nervi trigemini does and nigricans. not occur when epipterygoid is present. This species can be distinguished from its sister Aspideretes gangeticus (Cuvier, 1825) taxon Apalone (Apalone) spinifera by its DIAGNOsIS: A species of the genus Aspi- wider nuchal bone (four times wider than deretes with seven or more ossifications in long), jugal which contacts parietal on skull the second branchial horn of the hyoid, jugal surface and/or with squamosal in some in- never contacting parietal on skull surface, and dividuals, and six or fewer ossifications in the quadratojugal participating in processus second branchial horn of the hyoid. trochlearis oticum. Apalone (Platypeltis) ferox Aspideretes hurum (Gray, 1831) (Schneider, 1783) DIAGNOSIS: A species of Aspideretes with DIAGNOSIS: Members of the genus Apalone only one ossification in the second branchial which can most easily be distinguished from horn, eight ossifications in the corpus hyoi- 1 987 MEYLAN: TRIONYCHIDAE 93 dis, the dorsal margin of the apertura narium tended (more than 40% of hyohypoplastron extemum strongly emarginate, and the epi- width), the largest adult size is 200 mm or pterygoid (when present) contacting the pro- less (with one possible exception), the fora- otic in front of the foramen nervi trigemini men jugulare posterius is excluded complete- in some individuals. ly or partially from the fenestra postotica by a descending process of the opisthotic, and Aspideretes leithii (Gray, 1872) when the pterygoid contacts the foramen ner- DIAGNOSIS: Members of Aspideretes in vi trigemini it does so between the epipter- which some individuals have eight rather than ygoid (when present) and the parietal. nine neurals and in which the pterygoid, if CONTENT: In order to completely portray contacting the foramen nervi trigemini, does relationships and to encourage use ofthe name so between the epipterygoid (when present) Dogania for the highly derived species sub- and the quadrate. Further diagnosed by prim- plana, this tribe is considered to be com- itive conditions for those specialized features posed of two subtribes and three monotypic which are diagnostic for its congeners. genera. Aspideretes nigricans (Anderson, 1875) SUBTRIBE PELODISCINA, NEW NAME TYPE GENUS: Pelodiscus Gray, 1844. DiAGNOSIS: Members of Aspideretes in DiAGNOSIS: Members of Pelodiscini with which the jugal never contacts the parietal on seven callosities in the adult plastron, loca- the skull surface (true also of gangeticus), the tion ofthe last neural reversal highly variable foramen posterior canalis carotici interni is but always occurring at or anterior to neural located within a crest extending anterolater- six, jugal contacting squamosal in some in- ally from the basioccipital tubercle, the pa- dividuals, and rietal makes up more than 22 percent of the foramen palatinum posterius processus trochlearis oticum, and the epi- surrounded by the palatine. pterygoid is not known to contact the pala- CONTENT: Contains only Pelodiscus sinen- tine. sis. Nilssonia Gray, 1872 Pelodiscus Gray, 1844 TYPE SPECIES: Nilssonia formosa (Gray, TYPE SPECIES: Pelodiscus sinensis (Weig- 1869). mann, 1835). DIAGNOSIS: Members of Aspideretini with DIAGNOSIS: Same as for subtribe Pelodis- a single neural (fused one and two) between cina. the first pair of pleurals, the nuchal bone only CONTENT: Same as for subtribe Pelodis- two times wider than long, the last neural cina. reversal occurring at neural seven, the jugal always in contact with the parietal on the Pelodiscus sinensis Weigmann, 1835 skull surface, and the foramen intermandib- DiAGNOSIS: Same as for subtribe Pelodis- ularis caudalis never enclosed by the prear- cina. ticular. CONTENT: The single living species Nils- SUBTRIBE DOGANIINA, NEW NAME sonia formosa. TYPE GENUS: Dogania. Nilssonia formosa (Gray, 1869) DiAGNOSIS: Members of the tribe Pelo- discini with four plastral callosities, poster- DiAGNOSIS: As for the genus Nilssonia. iormost neural reversal occurring as far posterior as neural seven, long anterior processes TRIBE PELODISCINI, NEW NAME ofthe epiplastra, and postorbital bar less than TYPE GENUS: Pelodiscus Gray, 1844. one-fifth of orbit diameter. DiAGNOSIS: Trionychine turtles in which CONTENT: Two monotypic genera, Doga- the epiplastra are significantly anteriorly ex- nia and Palea. 94 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 186

Dogania Gray, 1844 Palea, new genus TYPE SPECIES: Dogania subplana (Geof- TYPE SPECIES: Palea steindachneri (Sieben- froy, 1809). rock, 1906). DiAGNosIs: Members of the subtribe Do- DiAGNosIs: Members of the subtribe Do- ganiina with a complete series ofnine neurals ganiina with the nuchal bone only two times (first and second fused) which divide all of wider than long, neural reversal always oc- the pleurals along the midline, eight ossifi- curring at the same neural (number 7), jugal cations in the corpus hyoidis, basisphenoid always contacting parietal on skull surface, often medially constricted, postorbital bar and epipterygoid contacting prootic anterior one-ninth of orbit diameter, and maxillae to the foramen nervi trigemini. contacting frontals along anterior margin of ETYMOLOGY: From the Latin palea, mean- orbits. ing wattles, in reference to the autapomorph- CONTENT: Contains only Dogania subpla- ic structures on the neck. na. CONTENT: Contains only Palea steindachneri (Siebenrock, 1906). Dogania subplana (Geoffroy, 1809) Palea steindachneri (Siebenrock, 1906) DIAGNOsIs: Same as for genus Dogania. DIAGNOsIs: Same as for genus Palea.

ACKNOWLEDGMENTS The progress of this study has relied on a Sciences Naturelles de Belgique, Brussels great number of people and to all of them I (IRSNB); Richard Leakey and Alec Duff- extend my thanks. My doctoral committee, McKay, Kenya National Museum (KNM); Walter Auffenberg, David Webb, Jon Reis- Pere Alberch and Jose Rosado, Museum of kind and Doug Jones has been supportive Comparative Zoology, Harvard (MCZ); E. R. and encouraging throughout the course of this Brygoo, Roger Bour, and J. P. Gasc, Mus- study. I have benefited from numerous dis- eum National d'Histoire Naturelle, Paris cussions of turtle systematics and phylogeny (MNHNP); D. F. E. Thys van den Auden- with my colleagues, Dennis Bramble, Chuck aerde, Musee Royal de l'Afrique Central, Crumly, Jim Dobie, Ren Hirayama, Howard Tervuren (MRAC); U. Rahm, Naturhisto- Hutchison, John Iverson, Peter Pritchard, and risches Museum, Basel (NHMB); J. L. Perret, especially Gene Gaffney. This contribution Museum d'Histoire Naturelle, Geneva has been improved through the efforts ofGene (NHMG); Franz Tiedemann and Heinz Gril- Gaffney, Howard Hutchison, John Iverson, litsch, Naturhistorisches Museum, Vienna Sam McDowell, Hobart Smith, Bob Webb, (NMW); Don Broadley, National Museum of and Barbara Werschek all ofwhom have read Zimbabwe (NMZB); M. S. Hoogmoed, Rijks- part or all of the manuscript critically. museum van Natuurlijke Historie (RMNH); For loans and/or access to museum collec- K. Klemmer, Natur-Museum Senkenberg, tions I am grateful to the following curators Frankfurt (SMF); Walter Auffenberg and and collection managers: C. W. Myers and Dave Auth, Florida State Museum (UF); Ar- staff, American Museum of Natural History nold Kluge and Dennis Harris, Museum of (AMNH); Jim Dobie, Auburn University Zoology, University of Michigan (UMMZ); Museum of Paleontology (AUMP); Nick Ar- George Zug, United States National Museum nold, Colin McCarthy, and Barry Clarke, (USNM); and Ulrich Gruber and Dieter British Museum of Natural History (BMNH); Fuchs, Zoologisches Sammlung der Baye- Harold Voris, Field Museum of Natural His- risches Staates, Munich (ZSM). For access to tory (FMNH); J. P. Gosse, Institut Royal des specimens in their private collections I thank 1 987 MEYLAN: TRIONYCHIDAE 95

John Iverson (JBI and JI), Ed Moll (EOM), This study has been supported by a grant Peter Pritchard (PCHP), Richard Etheridge from the Leakey Foundation, by Colonel (RE), and Ren Hirayama (RH). Barkau, by the Department of Zoology and Vince DeMarco made the histological the Florida State Museum, University of preparations. Frank Ipollito prepared figures Florida, and by the Department ofVertebrate 4, 5, 6, 8, 14E, 17, 18, 19, 20, and 21. Ian Paleontology and the James Walter Carter Brehney prepared figure 9. All or part of fig- Memorial Fund of the American Museum of ures 10, 11, 12, 14, 15, and 16 were made Natural History. To the staff of the Florida available by Gene Gaffney. Chester Tarka, State Museum I give special thanks for sup- Lorraine Meeker, Carol Gelber, and Bill port of many kinds. Weinstein provided technical assistance. For Anne there are never thanks enough.

Appendix 1. Specimens Examined The modal conditions of characters for EOM 2801, MNHNP 1866-151, MNHNP members of the Trionychidae listed in tables A-5226, MNHNP unnumbered, SMF 52770. 3, 11, and 17 are based on the following spec- Aspideretes hurum BMNH 68.2.12.15, BMNH with more than one 86.8.26.2, BMNH 81.7.8.4, BMNH 81.7.8.5, EOM imens. For specimens 2681, EOM 2811, EOM 2826, RE 2132, ZSM 26/ catalog number (BMNH, MNHNP) the ear- 1912. liest number is given. See acknowledgments Aspideretes leithii BMNH 70.7.11.1, EOM 2627, for explanation of museum acronyms. EOM 2819. Aspideretes nigricans BMNH 1929.12.23.1, Apalone ferox AMNH 129737, PCHP 343, BMNH 1929.12.23.2. PCHP 354, PCHP 1171, PCHP 1532, PCHP 1533, Chitra indica BMNH 47.3.6.21, BMNH 86.2.1.1, PCHP 1534, PCHP unnumbered, UF 10963, UF BMNH 87.3.30.11, BMNH 1926.12.16.1, BMNH 11124, UF 11126, UF 14270, UF 14363, UF 48.2.139, BMNHI 1974.2451, BMNH 1984.1276, 18932, UF 32999, UF 33434, UF 33436, UF BMNH unnumbered (mount 220), EOM 2625, 33447, UF 33453, UF 37545, UF 40534, UF EOM 2696, EOM 2699, IRSNB 18.8.88 (.?.?= 3295), 52886, UF 52887, UF 53172, UF 53173, UF MNHNP 1880.182, PCHP 1474, PCHP 1707, 53174, UF 53175, UF 53382, UF 53383, UF PCHP 2613, SMF 52768, SMF 52769. 53568, UF 53569, UF 53570, UF 53671, UF Cyclanorbis elegans BMNH 64.1.25.3, BMNH 53672, UF 53673, UF 54212, UF 54547, UF 64.8.8.9, BMNH 65.5.9.22, BMNH 1900.9.22.8, 55576, UF T-1203. BMNH 1906.11.16.2, BMNH 1909.10.15.5, Apalone mutica PCHP 1611, PCHP unnum- BMNHI 1949.1.9.58, BMNH 1954.1.14.2, BMNH bered, UF 55789, UF 57724, UF 57725, UF 57729, 1954.1.14.3, BMNH unnumbered, NMW 157, UMMZ 128086, UMMZ 155231. NMW 1436, NMW 1437, NMW 1438, NMW Apalone spinifera IRSNB 231, PCHP 1479, 1439, NMW 1440, NMW 1441, NMW 1504, PCHP 1480, PCHP unnumbered, UF 22392, UF RMNH 17968, SMF 37475. 37228, UF 40614, UF 43154, UF 43889, UF Cyclanorbis senegalensis BMNH 63.11.9.6, 45181, UF 45182, UF 45183, UF 45184, UF BMNH 1864.216, BMNH 65.4.6.10, BMNH 45356, UF 48257, UF 50811, UF 51093, UF 65.5.3.72, BMNH 65.5.3.73, BMNH 65.5.3.75, 51094, UF 55564. BMNH 65.5.9.19, BMNH 65.5.9.20, BMNH Amyda cartilaginea IRSNB 230, IRSNB 230B, 65.5.9.21, BMNH 1920.1.20.3225, BMNH IRSNB 231C, MNHNP 1883-1798, MNHNP 1920.1.20.3641, BMNH 1920.1.20.4118, BMNH 1883-1817, MNHNP unnumbered, NHMB 3767, 1947.3.6.23, BMNH 1949.1.3.57, BMNH un- PCHP 1310, RH 128, RH 129, RH 133, UF 57728, numbered, MCZ 42599, MNHNP-AC 1944-25 1, USNM 222522, ZSM 832/1920, ZSM 833/1920, NMW 1257/1, NMW 1257/2, NMW 1434, SMF ZSM 834/1920, ZSM 835/1920, ZSM 836/1920, 37474, ZSM 2509/0. ZSM 837/1920, ZSM 838/1920. Cycloderma aubryi BMNH 61.7.29, BMNH Aspideretes gangeticus BMNH 48.2.21.41, 63.6.13.5, FMNH 98752, MCZ 145308, MHNG BMNH 80.1.28, BMNH 86.8.26.1, BMNH 3 un- unnumbered, MNNHNP 1889-384, MNHNP 1922- numbered specimens, EOM 2663, EOM 2664, 365, MNHNP 1930-362, MNHNP 1944-265, 96 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 186

MNHNP-AC unnumbered, MRAC 945, MRAC BMNH 99.1.12.7, BMNH 1974.2330, BMNH un- 2581, MRAC 3050, MRAC 14621, MRAC 14623, numbered, EOM 2675, NHMB 183, NMW 1857, MRAC 14662, MRAC 19212, MRAC 19813. RMNH 21839, RMNH unnumbered, USNM Cyclodermafrenatum BMNH unnumbered (type 231523. of Aspidochelys livingstonz), MCZ 50359, NHMB Pelodiscus sinensis BMNH 62.2.23.9, BMNH 16692, NMZB 1245, NMZB 6623, SMF 33700, 73.7.30.19, BMNH unnumbered, NHMB C 1438, TM unnumbered, UF 52704. NHMB C1439, NHMB C2659, NHMB 3173, Dogania subplana BMNH 53.5.38, BMNH NMW 1868, RH 307, SMF 69850, UF 55259, UF 60.3.19.1045, BMNH 81.10.10.12, BMNH 55265, UF 55266, UF 55267, UF 55270, UF 1929.7.3.10, BMNH unnumbered, MNHNP 55271, UF 56116, USNM 68476, USNM 68833, A5 182, MVZ 95937, NMW 1871, PCHP unnum- ZSM 144/1908, ZSM 428/1911, ZSM 429/1911, bered, RMNH unnumbered, UF 56317, USNM ZSM 430/1911, ZSM 3020/0, ZSM 3041/0, ZSM 40005, USNM 70835, USNM 222523. 3043/0, ZSM 3044/0. Lissemys punctata BMNH 69.8.28.10, BMNH Rafetus euphraticus BMNH 50.12.1.1, BMNH 88.12.3.4, BMNH 1972.2067, BMNH 1972.????, 50.12.21.16, BMNH 54.5.11.17, BMNH MNHNP A5169, MNHNP-AC 1880-472, NHMG 93.10.14.1,BMNH 1935.5.9.8,NMW 127,NMW 615.87, NHMG 615.88, NHMG 1557.19, NMW 130, NMW 131, NMW 132, NMW 204, NMW 1872, PCHP 1437, UF 55788, UF 56017, UMMZ 1446, NMW 1861, NMW 1862. 129396, UMMZ 129896, USNM 061093, USNM Rafetus swinhoei BMNH 73.7.30.125. 061094. Trionyx triunguis BMNH 62.3.20.8, BMNH Nilssonia formosa BMNH 68.4.3.142, BMNH 65.4.6.9, BMNH 1911.7.27.1, BMNH 1954.1.14.4, 81.7.8.3, BMNH 87.3.30.12, BMNH 87.3.30.20, IRSNB 3299, KNM ER 8123, KNM 3 unnum- BMNH 91.11.26.6. bered specimens, MNHNP A5186, MNHNP Palea steindachneri BMNH 1930.4.3.2, A5242, MRAC 5446, MRAC 11978, MRAC MNHNP 1980/1476, MNHNP unnumbered. 12324, MRAC 12329, MRAC 14479, MRAC Pelochelys bibroni BMNH 60.4.19.1444, BMNH 15408, MRAC 15651, MRAC 16560, NMW 203, 64.9.28.5, BMNH 80.4.25.6, BMNH 87.3.30.15, USNM 231704.

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