First Known Extant Elseya Specimens (Testudines: Chelidae) Bearing Rounded Ischial Blade Morphology – Cryptic Species or Novel Aberrancy?

Abstract

The inclusion of osteological characters as an essential component of the diagnosability of Australasian chelid turtles on a species level has taken on a higher priority in the last three decades. Genetic and morphological investigations continue to reveal a significantly enriched level of turtle species biodiversity in Australia and New Guinea than previously suspected.
One of the characters involves that of the plastral scar and suture of the ischial blade with the visceral surface of the xiphiplastron, distinctly different between the Elseya/Emydura lineage and that of Chelodina/ Pseudemydura. In this brief communication we here note and assess the first known documented examples of Elseya specimens in which the ischial morphology superficially resembles that of the latter group in bearing a semi-circular posterior ischial blade; all specimens are adults from a single river system, potentially indicating the presence of a cryptic taxon in the Elseya rhodini complex.