The Australian gulf snapping turtle Elseya lavarackorum (Testudines: Chelidae) revisited—Is the late Pleistocene fossil species extant?

Abstract

Disagreement exists on the taxonomic identity of the extant populations of the Australian Elseya referred to in 1992 as the gulf Elseya (= Elseya sp. aff. dentata [Nicholson]). The extant form has since 1997 been considered conspecific with the late Pleistocene fossil Elseya lavarackorum (White and Archer, 1994). Recently it has been considered a new species, Elseya oneiros Joseph-Ouni et al., 2020, conspecific with another fossil found in the same site and stratum as Elseya lavarackorum. Here we re-examine the fossil material and reassess the characters used by previous authors in an attempt to decide the issue. We find that the anterior bridge suture with the carapace of the fossil Elseya lavarackorum is associated with extensive and prominent plastral elements, which has led to misinterpretation of characters associated with this structure. We furthermore show that interindividual variation in sulci patterns is so great as to render them of little taxonomic value. On the basis of (a) deviation of the anterior shape of the carapace from ovoid such that, in aged individuals, the most anterior point of the carapace occurs at marginal scutes M2 (a resultant nuchal bay occurs in such individuals); (b) the typical absence of a cervical scute; (c) no evidence of a medial constriction in the anterior bridge strut suture; and (d) absence of evidence of any other informative variation of taxonomic value; we conclude that the decision to consider the late Pleistocene (ca 23 kyr old) fossil and the extant Elseya sp. aff. dentata [Nicholson] as Elseya lavarackorum (White and Archer, 1994) as conspecific should stand.