Elseya dentata has various common names including Northern Australian snapping turtle and deep shelled snapper (Cann, 1998; Cogger, 1992; Iverson, 1992). It is a side-necked turtle or pleurodire (see Gaffney website for more information on pleurodires and cryptodires), and within this group it is a member of Chelidae (see also Chelus). For further information on Australian chelids see Cann (1998) and Goode (1967).

As currently interpreted (Gaffney and Meylan, 1988), Chelidae is the sister group to Pelomedusoides (see Podocnemis, Pelusios, and Hamadachelys); these groups are united by the unique characters of Pleurodira including the processus trochlearis oticum, a jaw muscle pulley arrangement (see Gaffney website). A recent systematic analysis based on molecular data (Shaffer et al., 1997) recognizes two clades within Chelidae, one South American and one Australian; however, morphology (Gaffney, 1977; Gaffney and Meylan, 1988) suggests that the Australian Chelodina is most closely related to the South American Hydromedusa.

Chelidae is diagnosed by unique features of the skull that can be seen in Elseya. The cheek emargination is developed from the ventral margin and extends posteromedially to a greater extent than in any other turtle group. Probably related to this is the loss of the quadratojugal bone, a cheek element lacking in all chelids.

Elseya is usually considered to be closely related to or synonymous with Emydura because their skulls are very similar. Skull morphology of all chelids is described in Gaffney (1977, 1979), with skull figures of Elseya and/or Emydura in Cann (1998) and Cann and Legler (1994). See Gaffney (1979: figs. 12,38, 40, 43, 55, 69, 145, and 150) for labeled drawings of the skull of Elseya and sectioned skulls of Emydura. The most current treatments of the fossil record of the Elseya/Emydura group are Megirian and Murray (1999), Thompson and Mackness (1999), and Thomson (2000).

An interesting comparison within the chelids is between the presumably more generalized skull of Elseya and the very derived skull of Chelus. Elseya and Emydura have skulls that are interpreted as exhibiting more primitive character states (Gaffney, 1977) than the other chelids, like Chelus, Hydromedusa and Chelodina. In Chelus the skull is very flat in contrast to the much higher skull seen in Elseya and the outgroup Pelomedusoides. The cheek emargination of Elseya is relatively primitive because it does not extend posteriorly and medially as it does in Chelus and other chelids. Furthermore, nasal bones are present in Elseya but lost in Chelus.

This specimen was made available to the University of Texas High-Resolution X-ray CT Facility for scanning by Dr. Chris Bell of The University of Texas at Austin and Dr. Gene Gaffney of the American Museum of Natural History. Funding for scanning was provided by a National Science Foundation Digital Libraries Initiative grant to Dr. Timothy Rowe of The University of Texas at Austin.

The specimen was frozen in liquid nitrogen and then scanned by Richard Ketcham and Matthew Colbert on 8 September 2000 along the coronal axis for a total of 246 512x512 pixel slices. Each slice 0.105 mm thick, with an interslice spacing of 0.105 mm and a field of reconstruction of 27.527 mm. The animations displayed were reduced for optimal Web delivery from the original, much higher resolution CT data.

Literature

Cann, J. 1998. Australian Freshwater Turtles. Beaumont Publishing Pte Ltd., Singapore. 292 pp.

Cann, J., and J. M. Legler. 1994. The Mary River tortoise: a new genus and species of short-necked chelid from Queensland, Australia (Testudines: Pleurodira). Chelonian Conservation and Biology 1:81-96.

Cogger, H. G. 1992. Reptiles and Amphibians of Australia. Fifth Edition. Reed Books, Sydney. 775 pp.

Gaffney, E. S. 1977. The side-necked turtle family Chelidae: A theory of relationships using shared derived characters. American Museum Novitates 2620:1-28.

Gaffney, E. S. 1979. Comparative cranial morphology of recent and fossil turtles. Bulletin of the American Museum of Natural History 164:65-375.

Gaffney, E. S., and P. A. Meylan. 1988. A phylogeny of turtles; pp. 157-219 in M. J. Benton (ed.), The Phylogeny and Classification of the Tetrapods, Volume 1: Amphibians, Reptiles, Birds. Systemtics Association Special Volume 35A, Clarendon Press, Oxford.

Goode, J. 1967. Freshwater Tortoises of Australia and New Guinea (in the Family Chelidae). Lansdowne Press, Melbourne. 154 pp.

Iverson, J. B. 1992. A Revised Checklist with Distribution Maps of the Turtles of the World. Privately printed, Richmond, Indiana.

Megirian, D., and P. Murray. 1999. Chelid turtles (Pleurodira, Chelidae) from the Miocene Camfield Beds, Northern Territory of Australia, with a description of a new genus and species. The Beagle, Records of the Museums and Art Galleries of the Northern Territory 15:75-130.

Shaffer, H. B., P. Meylan, and M. L. McKnight. 1997. Tests of turtle phylogeny: molecular, morphological, and paleontological approaches. Systematic Biology 46:235-268.

Thomson, S. 2000. A revision of the fossil chelid turtles (Pleurodira) described by C. W. De Vis, 1897. Memoirs of the Queensland Museum 45:593-598.

Thomson, S., and B. Mackness. 1999. Fossil turtles from the early Pliocene Bluff Downs Local Fauna, with a description of a new species of Elseya. Transactions of the Royal Society of South Australia 123:101-105.

Links

Gene Gaffney's Phylogeny of Turtles (AMNH) (requires Flash plug-in)

Peter Meylan's Testudines Page on the Tree of Life

None available.