A new scincid lizard from the Miocene of northern Australia, and the evolutionary history of social skinks (Scincidae: Egerniinae)

ABSTRACT

The Egerniinae (formerly the Egernia group) is a morphologically diverse clade of skinks comprising 61 extant species from eight genera, spread across Australia, New Guinea, and the Solomon Islands. The relatively large size and robustness of many egerniines has meant that they fossilize more readily than other Australian skinks and have been more frequently recorded from paleontological excavations. The Riversleigh World Heritage Area of northeastern Australia has yielded multiple egerniine fossils, but most are isolated jaw elements, and only one taxon (‘Tiliqua’ pusilla) has been formally described. Articulated remains recently recovered from the mid-Miocene AL90 site (14.8 Ma) at Riversleigh are here described as Egernia gillespieae and represent the first opportunity to describe the morphology of a significant portion of a single individual of a fossil member of the Egerniinae. We include this fossil and ‘T.’ pusilla in an integrated analysis of morphology and published molecular data to assess their relationships and to provide calibration points for the timing of the egerniine radiation. Our calibrated tree combining molecular and morphological data suggests that the modern Australian radiation dates to the end of the Eocene (34.1 Ma). Both fossils are within the Australian crown clade Egerniinae: Egernia gillespieae is placed close to species of the living genus Egernia, whereas ‘Tiliqua’ pusilla likely sits basal to the divergence of the clade inclusive of Tiliqua and Cyclodomorphus. The fossils thus provide direct evidence that the Australian radiation of the Egerniinae was well underway by the mid-Miocene.

ACKNOWLEDGMENTS

Support for The Riversleigh Fossil Project comes from the Australian Research Council (LE0989067, DP0985214, DP0664621, LP0989969, LP100200486, DP1094569, DP130100197, DE130100467, DP170101420), Xstrata Community Partnership Program North Queensland, Outback at Isa, Mount Isa City Council, Queensland Museum, University of New South Wales, Environment Australia, Queensland Parks and Wildlife Service, the CREATE fund at University of New South Wales, and the Waanyi people of northwestern Queensland. The authors would like to acknowledge the numerous field teams that have collected fossils from Riversleigh World Heritage Area over the last 40 years; P. Stokes for photographing the Egernia gillespieae specimens and comparative material; Adelaide Microscopy for access to their Skyscan-1076 for micro-CT; I. Douvartzidis for assisting with the micro-CT scanning; M. Gardner for discussions on Egernia diversity; Australian Biological Resources Study National Taxonomy Research Grant Program for a Student Travel Grant to K.T.; and the Society of Vertebrate Paleontology for the Jackson School of Geosciences Travel Award to K.T., to present this research at the 77th Annual Meeting of Society of Vertebrate Paleontology in Calgary. We also thank the Willi Hennig Society for making TNT freely available, A. Čerňanský, an anonymous reviewer, and the editor J. Sterli for their comments and suggestions, which improved the manuscript.

ORCID

Kailah M. Thorn http://orcid.org/0000-0002-0645-835X

Michael S. Y. Lee http://orcid.org/0000-0002-3905-0887