Thomson, S. A. 2000 06 30: A Revision of the Fossil Chelid Turtles (Pleurodira) Described by C.W. De Vis, 1897. Memoires of the Queensland Museum 45(2):593-598. Brisbane. ISSN 0079-8835.

S.A. Thomson, Applied Ecology Research Group and CRC for Freshwater Ecology, University of Canberra, Canberra, ACT, 2601, Australia. 29 October, 1999.

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With increasing knowledge of the morphology of Australian chelid turtles and major changes in taxonomy it has become necessary to assign, where possible, the fossil species described last century by C.W. de Vis. It was found that four of these, Chelymys uberima, C. arata, C. antiqua and Pelecomastes ampla, were synonymous, with C. uberima being the senior synonym. Chelymys uberima was determined to be a member of the Elseya whose affinities lie with the Elseya lavarackorum group of species. The paralectotypes of Chelymys antiqua were found to be a new species of the genus Rheodytes and sister to R. leukops. These specimens are described as a new species. Chelodina insculpta was found to be a valid taxon whose affinities probably lie with C. expansa. Keywords: Testudines, side-necked turtle, Chelidae, Miocene, Pleistocene.

Summary  

     The identification of fossil forms is an important addition to the understanding of the evolution and zoogeography of any species group. This is made difficult when the taxonomy of the extant forms is not well defined, as is the case for the Australian chelid turtles (Cogger et al., 1983; Thomson et al., 1997). With some recent advances on the skeletal morphology of chelids (Thomson & Georges, 1996; Thomson et al., 1997) it is now possible, and appropriate, to examine the fossil forms that have been formally described. For example, the recent description of a fossil turtle from Riversleigh, Elseya lavarackorum (White & Archer, 1994), and the subsequent discovery of a living population of this species (Thomson et al., 1997).

     Fossil turtles in Australia have for many years been ignored due to the lack of detailed description of extant species. Rarely have skeletal diagnoses accompanied descriptions of the Australian chelid turtles, even those more recent. This makes the identification and placement of fossils difficult or impossible.

     A second verified record now comes from the South Alligator River system, approximately 400 km east of the Daly River site. There, in Yellow Waters billabong on Jim Jim Creek, a single female (CSIRO R. No. 320) was caught by a CSIRO fauna survey team on 5 November 1971. the specimen (Fig. 1), deposited in the museum of CSIRO's Division of Wildlife Research, Canberra, is large, having a carapace length of 45.6 cm. This compares with ca 48-50.5 cm for the largest New Guinea specimens (Walther 1922; Schultze-Westrum 1963). Other dimensions, taken from life, are: carapace breadth (including marginals) 36.5 cm; total height (carapace + plastron) 14.8 cm; head length (to base of crown) 15 cm; head width 8.1 cm; head + neck length (to gular shields of plastron) 18.5 cm; fore-limb length (posterior margin of the flipper) 26.4 cm; hind-limb length (anterior margin of the flipper) 25.3 cm; tail (to base of anal shields of plastron) 16.9 cm long, with 12 or 13 dorsal scute bands. Soft part colours: shell, limbs, head and tail, mid to dark olive-brown dorsally, grading to cream ventrally (fleshy scream on plastron); iris mid blue-green-grey. Except for the reduced number of caudal scutes, quoted at 14-16 for New Guinean specimens by de Rooij (1915), the South Alligator specimen appears to be identical with New Guinean forms.

     Apart from Elseya lavarackorum and E. nadibajagu Thomson & Mackness, 1999, only five other species of fossil chelid turtles have been described from Australia (Gaffney, 1981), all by C. W. de Vis (1897). Gaffney (1981) found that the available material was indeterminate below family or genus level was the last to revise the de Vis specimens. Three of the species, Chelymys uberima, C. antiqua and C. arata, were identified as Emydura sp. (= Emydura + Elseya of Gaffney, 1977); another, Chelodina insculpta, was identified as Chelodina sp.; and the last, Pelocomastes ampla, could not be identified to family (Gaffney (1981). These species were all described from fragmentary material from the Darling Downs with no holotypes designated (de Vis, 1897), hence Gaffney (1981) nominated lectotypes from each set of fragments and designated the rest of the specimens as syntypes. These specimens were originally diagnosed using differences in sulci (de Vis, 1897) but it seems that they were actually arranged according to scute ornamentation (Gaffney, 1981). This is a highly variable character and I agree with Gaffney (1981) that it is of little phylogenetic significance.

     In this paper the fossil turtles described by de Vis (1897) are reanalysed and, where appropriate, resurrected or placed in synonymy. They are in their correct genera using previously published diagnostic characters and their affinities and phylogenetic implications discussed.

The purpose of this paper is to solve the nomenclatural problems associated with having described specimens of unknown affinity. It is not the purpose of this paper to present a review of the living genera with respect to the fossils.

     Turtles representing all extant Australasian species have been borrowed from museums, collected or otherwise obtained, and skeletonised as per methods outlined in Thomson et al. (1997). This turtle collection of some 350 specimens is housed at the University of Canberra. Characters described in Thomson et al. (1997) were used for diagnosis and the fossils were then assigned to genus and their affinities demonstrated. A complete list of specimens examined can be found in Thomson et al. (1997). Further specimens with locality data will be presented in a future major analysis of the Elseya genus.

Material. Holotype: none set (de Vis, 1897). Lectotype: QMF9040 by subsequent designation (Gaffney, 1981) (Fig. 1.). Paralectotypes: QMF1104, 1105 by subsequent designation (Gaffney, 1981). Lectotype of Chelymys arata QMF16-1099B by subsequent designation (Gaffney, 1981) (Fig. 1B). Lectotype of Pelocomastes ampla QMF1102D by subsequent designation (Gaffney, 1981) (Fig. 1C-D). Lectotype of Chelymys antiqua QMF16-1106E by subsequent designation (Gaffney, 1981).

Horizon. Pliocene
Locality. Darling Downs, Queensland, Australia.
Discussion. Material consists of: QMF9040 (Fig. 1A) nuchal, right peripherals 1-3, left and right pleural 1, articulated. QMF1104 numerous unarticulated carapace fragments including peripherals and pleurals. QMF1105 numerous unarticulated plastral fragments.

The lectotype assigned by Gaffney (1981) is suitably diagnostic and can be recognised as an Elseya without difficulty. The first vertebral scute is significantly wider than the second (Fig. 1A), a character found only in the Elseya and Chelodina (Thomson et al., 1997). The Chelodina have either an anterior bridge strut restricted to the peripheral bones and not continuing onto the pleural bones, eg C. longicollis group except C. novaeguineae (Thomson, in press; Thomson et al., in press). Or the strut continues onto the pleurals but not contributed to by the rib gomphosis, although it crosses it in some species, is wide throughout its length with a significant enlargement at the medial end, C. expansa group and C. novaeguineae (Thomson, in press; Thomson et al., in press). The structure of the anterior bridge struts in Chelymys uberima is consistent with neither of the Chelodina conditions and is similar in structure to that described for the Elseya lavarackorum group (Thomson et al., 1997)(Fig. 2.). The structure of the first pleural and the indentation at the nuchal region places this species in the Elseya lavarackorum group of species. The fact that this species has a cervical scute is not unusual among fossil Elseya, particularly those from western flowing drainages. Specimens in the South Australian Museum from Lake Palankarina and Lake Ngapakaldi all exhibit this feature and may represent an entire extinct radiation of Elseya turtles.

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