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