Egernia gillespieae and the history of Australia’s social skinks

Egernia gillespieae and the history of Australia’s social skinks

Twenty five years ago a large chunk of the Carl’s Creek Limestone at the Riversleigh World Heritage Fossil Area was blown off of the edge of Allan’s Ledge 1990 site. It then began a long journey back to the University of New South Wales PANGEA facility to undergo acid preparation to unlock its valuable secrets. Inside this lump of rock, block 94H, was a partial skull of Egernia gillespieae, the key to timing the origins of Australia’s social skinks. Egernia gillespieae was named in this new paper out in the Journal of Vertebrate Paleontology, after the palaeontologist, and fossil preparator, Dr Anna Gillespie. Dr Gillespie has been an integral element of the PANGEA lab, responsible for preparing thousands of fossils from Riversleigh World Heritage Area.

Fossil squamates (lizards and snakes) are rarely recovered so complete from Australian palaeontological excavations. Dr Gillespie’s keen eye, and care for all fossils regardless of their species, size, or where they fit in a skeleton, has meant that an almost complete individual skull representing Egernia gillespieae can be assembled. This is the first Australian fossil skink to be described so completely, most only known from half-mandibles, isolated frontals, or disarticulated post-crania.

Having a near-complete individual skull presents a novel opportunity to examine these elements in context with the living Egernia and their nearest relatives, which include ‘land mullets’, spiny-tailed skinks, bluetongues, and shinglebacks. Egernia gillespieae is most similar to living Egernia striolata, the tree skinks. The paper also examined Australia’s oldest fossil bluetongue lizard, Tiliqua pusilla, which came from another site at Riversleigh and is of a similar age. A number of questions were asked, covering differences in shape and the presence or absence of different features in each species, both alive and extinct. These morphological characters were then analysed with molecular data (DNA and mitochondrial), imploring Parsimony and Bayesian analyses, to find the simplest, and the most likely phylogenetic trees of Australia’s social skinks.

Having fossils to calibrate the family tree of Australia’s social skinks has deciphered that our big bluetongues and pink tongues, Tiliqua and Cyclodomorphus, split from Egernia as early as 25 million years ago. Unexpectedly, we also found that Australia’s smallest living Tiliqua, the pygmy bluetongue, Tiliqua adelaidensis is sister to one of the largest, the shingleback Tiliqua rugosa.

This study, was made possible due to the keen eye of Dr Anna Gillespie, numerous UNSW field teams venturing out to northwestern Queensland to blast the limestone, and a team of palaeoherpetologists from Flinders University and the South Australian Museum. It represents the first step toward unravelling the evolutionary history of Australia most iconic herpetofauna.