Two new species of ektopodontid marsupial from the lower deposits of the Etadunna Formation (latest Oligocene), South Australia and a phylogenetic hypothesis for the Ektopodontidae

Abstract

Abstract Molar morphologies of the latest Oligocene genera, Chunia and Ektopodon, are easy to distinguish, but species determinations are more difficult. As more specimens have been collected, more maxillary fragments with molars and/or alveoli and a portion of the rostrum preserved are available. With a suite of maxillae now known, new ektopodontid features have revealed themselves, including the shortening of the rostrum compared to other families of contemporary possums. The facial angulation represented by the flexure of the rostrum at the boundary between P3 and the molar row results in the rostrum being angled differently than the molar row. Ektopodontids have a significantly greater angulation and thus shorter faces, compared to that seen in contemporary phalangeriform possums. Two new species of the genus Chunia, from the lower Etadunna Formation, South Australia, can be distinguished from the type species, Chunia illuminata, of the Ditjimanka Local Fauna. Differences in molar morphologies and the degree of facial angulation distinguish a new species of Chunia from the lowest faunal zone and the Minkina Local Fauna (facial angulation of 52°) from C. illuminata from the next higher faunal zone (Ditjimanka Local Fauna), which has a greater facial angulation of 63°, while a second new species of Chunia, also from the Dijimanka Local Fauna, has a facial angulation of 58° and intermediate molar traits. The degree of facial shortening is a valid discriminator between species of ektopodontid marsupials as it coincides with the species level differences in dental morphology. Additionally, C. omega from the Tarkarooloo Local Fauna is placed in new genus, Ngathachunia, as it is outside of the hypodigms for both of the previously described genera, Chunia and Ektopodon. A well-supported phylogenetic hypothesis for the family indicates the species of Ektopodon form a monophyletic clade, while the species of Chunia are paraphyletic. Judd A. Case [jcase@ewu.edu], Department of Biology, Eastern Washington University, Cheney, WA 99004, USA. Case, J.A., Month, 202X. Two new species of ektopodontid marsupial from the lower deposits of the Etadunna Formation (latest Oligocene), South Australia and a phylogenetic hypothesis for the Ektopodontidae. Alcheringa XXX, X–X. ISSN 0311-5518.