Australian chelid turtle taxonomy is poorly known and much in need of review (Cogger et al. 1983; Thomson et al. 1997). Electrophoretic surveys have revealed that in some instances, currently accepted species boundaries are difficult to justify and what are currently regarded as single species are in fact two or more species (Georges & Adams 1992, 1996).

    The detailed morphological analysis required to verify these findings has not been completed (Thomson & Georges, 1996; Thomson et al. 1997), and until recently it was not possible to distinguish even between extant short-necked genera on the basis of osteological characters (Gaffney, 1977). The poor knowledge of osteological characters suitable for distinguishing the genera of extant forms makes the identification of fossils, many incomplete, difficult (Thomson et al., 1997). In many instances, chelid fossils have been assigned to either Chelodina or Emydura, with little or no evidence presented to eliminate the possibility that the short-necked forms among them may be Elseya, Rheodytes or Elusor.

     Specimens of the chelid turtle species identified using electrophoresis by Georges & Adams (1996) were obtained from museums, the Conservation Commission of the Northern Territory and the University of Canberra. Where possible the voucher specimens of Georges & Adams (1992, 1996) were utilised to avoid incorrect identification. The specimen collection was supplemented by limited field sampling. All specimens were skeletonised and assessed by methods outlined in Thomson et al. (1997).

     The fossil specimens from Bluff Downs were collected as part of an on-going study of the palaeoecology of the Bluff Downs Local Fauna by one of the authors (BM). Specimens are currently held at the Queensland Museum. Each was examined to determine the presence of character states for the characters identified as being diagnostic at the level of genus for extant taxa. The fossil specimens were then assigned to genus. Throughout this paper, names of the bony elements of the shell and the overlying scutes follow those of Zangerl (1969).

     Five characters were identified as diagnostic at generic level. Where polarity is indicated, it was determined by comparison with South American chelids and African pelomedusids in a cladistic analysis to be presented elsewhere (Thomson & Georges, in prep.). Only those characters relevant to the identification of the fossil specimen are presented.

Anterior Bridge Struts
Character A. Contact with Pleural 1
A0: In the primitive state, the posterior edge of the bridge-carapace suture runs parallel and adjacent to the rib/gomphosis of pleural 1.
A1: In the derived state, the posterior edge of this suture contacts the rib/gomphosis at its anterior end, but is set at a forward divergent angle of between 15and 50 . This angle is most pronounced in Emydura, least so in Rheodytes.

Character B. Bridge suture shape
B1: The anterior and posterior edges of the bridge-carapace suture diverge from their point of congruence closest to the vertebral column. The widest extent of the suture is distal to the vertebral column and there is no medial constriction.

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