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

The Egerniinae (formerly the <i>Egernia</i> 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 (‘<i>Tiliqua’ pusilla</i>) has been formally described. Articulated remains recently recovered from the mid-Miocene AL90 site (14.8 Ma) at Riversleigh are here described as <i>Egernia gillespieae</i> 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 ‘<i>T.</i>’ <i>pusilla</i> 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: <i>Egernia gillespieae</i> is placed close to species of the living genus <i>Egernia</i>, whereas ‘<i>Tiliqua</i>’ <i>pusilla</i> likely sits basal to the divergence of the clade inclusive of <i>Tiliqua</i> and <i>Cyclodomorphus</i>. The fossils thus provide direct evidence that the Australian radiation of the Egerniinae was well underway by the mid-Miocene.