The Oldest Genus of Scincid Lizard (Squamata) from the Tertiary Etadunna Formation of South Australia

-Recent expeditions to the Lake Palankarinna rea of South Australia resulted in the oldest and only known extinct skink genus in Australia. The holotype of a new genus and species, Proegernia palankarinnensis, was collected from the basal portion of the Late Oligocene Etadunna Formation from the Minkina Local Fauna. Additional scincid fossils previously recovered from higher levels in the formation include material that may be referable to Proegeria. Proegernia is placed in the Egeria group within the Australian Lygosominae, based mainly on its closed Meckelian groove with the apex of the splenial notch low on the lingual surface. However, the apex is markedly more anterior in Proegernia than in any living Egernia group taxon. Proegernia possesses characters suggestive of its position as a stem taxon for later occurring skinks of the Egernia species groups. Even so, overall stage of evolution suggests that the Scincidae of Australia had a long evolutionary history prior to the Late Oligocene, a contention supported by previous molecular studies. The Scincidae are the most abundant and diverse lizards in Australia. At least 38 genera and 378 species are recognized (Cogger, 2000) in Australia, and additional species are known but not yet described (e.g., Storr et al., 1999). Skink species range from 0.4 g and 35 mm snout-vent length (SVL) to 1000 g and 371 mm SVL (Hutchinson, 1993). The diversity of skink habitat preferences includes terrestrial, fossorial, arboreal, saxicoline, and semiaquatic. Skink diets are also diverse as reflected by various tooth morphologies, some of which are characteristic of lineages, whereas others are related to prey type (e.g., Estes and Williams, 1984). Skink systematics emphasize cranial features and include a cranium covered with enlarged dermal plates, paired premaxillae, and parietals with a descending process that abuts against the epipterygoids (Estes et al., 1988). In fossil deposits, cranial material is often scarce or fragmentary (Smith, 1976), so most fossil skinks are identified by the peglike teeth and enlarged coronoid process of the dentary (Estes, 1983). Although these characters are shared with related groups (cordylids and anguids; Lee, 1998), most skinks are distinguishable by mode of tooth replacement and tooth-crown shape (Edmund, 1969; Lang, 1991). Given the diversity of Australian scincids, one might expect a long evolutionary history on the 2 Corresponding Author. continent. However, because of the isolation of Australia, one might also postulate rapid diversification caused by reduced competition and limited predators. Based upon immunological data, phylogenetic divergence of major scincid groups is postulated to have occurred during the earliest Tertiary, suggesting divergence of the family during the Cretaceous (Baverstock and Donnellan, 1990). Unfortunately, the fossil record is limited. A medial to late Eocene femur from the Rundle Formation, central east Queensland was reported by Hocknull (2000), who felt that the specimen warranted assignment to scincomorphs but not enough morphological data were preserved for assignment to the Scincidae. Estes (1984) described skinks from the Late Oligocene Etadunna Formation, represented by dentary, maxillary, and parietal elements, which until now were the oldest well-documented skink fossils. Estes identified these specimens as Egernia and Tiliqua, but both were derived from higher in the stratigraphic section (Ditjimanka L.F.) than that described herein. Skinks from the early to medial Miocene Riversleigh assemblages were described by Hutchinson (1992) and include the Egernia frerei (= Egernia major) species group, the Egernia striolata species group, and Tiliqua (Hutchinson, 1992; Shea and Hutchinson, 1992). These Egernia comparisons were based upon plesiomorphic morphology or characters (especially dentition) that are phenetically similar to those of certain Egernia but of unclear AUSTRALIAN TERTIARY SCINCID TABLE 1. Comparative species examined and Egernia species groups assignments.