A new ektopodontid possum (Diprotodontia, Ektopodontidae) from the Oligocene of central Australia, and its implications for phalangeroid interrelationships

The Ektopodontidae are an enigmatic group of phalangeroid marsupials known from the late Oligocene to the Early Pleistocene of Australia. Although represented to date only by isolated teeth and several partial dentaries and maxillae, their highly distinctive dental morphology has allowed three genera and nine species to be distinguished. Here, we describe possibly the geologically oldest ektopodontid, Chunia pledgei sp. nov., from the Oligocene Pwerte Marnte Marnte fossil locality of central Australia. Phylogenetic analyses of Phalangeroidea, using 80 primarily dental characters framed by a molecular scaffold, support placement of the new taxon in the genus Chunia. The analyses failed to recover species of the genus Durudawiri in a monophyletic Miralinidae, indicating that they require systematic review. We also transfer the purported basal phalangerid Eocuscus sarastamppi to Miralinidae (Miralina sarastamppi comb. nov.). Additionally, the M1 specimens used to describe the Early to Middle Miocene miralinid genus Barguru, and three species therein, are re-identified as deciduous third premolars from early macropodoids. These findings imply that the Miralinidae are known only from the late Oligocene, whereas the oldest named phalangerids are from the Early Miocene. From a functional consideration of ektopodontid dental morphology, we infer support for prior suggestions of a granivorous and/or frugivorous diet for them. The relative stage-of-evolution expressed by the new taxon is comparable to those in the lower faunal zones of the Namba and Etadunna formations, which supports a late Oligocene age for the Pwerte Marnte Marnte assemblage.