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, <i>Chunia pledgei</i> 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 <i>Chunia</i>. The analyses failed to recover species of the genus <i>Durudawiri</i> in a monophyletic Miralinidae, indicating that they require systematic review. We also transfer the purported basal phalangerid <i>Eocuscus sarastamppi</i> to Miralinidae (<i>Miralina sarastamppi</i> comb. nov.). Additionally, the M1 specimens used to describe the Early to Middle Miocene miralinid genus <i>Barguru</i>, 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.

袋貂超科（Phalangeroidea）下的隐袋貂科（Ektopodontidae）是一类神秘的有袋类类群，其化石记录分布于澳大利亚渐新世晚期至更新世早期地层。尽管目前仅发现孤立牙齿、多件下颌骨残段与上颌骨残片，但凭借其极具辨识度的牙齿形态，学界已区分出3属9种。本文记述了可能是地质年代最古老的隐袋貂科物种——Chunia pledgei 新种（sp. nov.），其化石发现于澳大利亚中部渐新世的Pwerte Marnte Marnte化石点。本次基于分子框架下的80个主要牙齿性状对袋貂超科开展系统发育分析，结果支持将该新分类群归入春尼袋貂属（Chunia）。分析未能将杜鲁达维里属（Durudawiri）的物种归入单系的米拉林科（Miralinidae），表明该类群需要进行系统分类修订。我们还将原本被认为是基底袋貂科的Eocuscus sarastamppi转移至米拉林科，组合为Miralina sarastamppi 新组合（comb. nov.）。此外，原本用于记述早中新世至中中新世米拉林科巴古鲁属（Barguru）及其3个物种的第一上臼齿（M1）标本，被重新鉴定为早期袋鼠类（macropodoids）的乳第三前臼齿（deciduous third premolars）。这些发现意味着米拉林科仅发现于渐新世晚期，而已知最古老的命名袋貂科物种则来自早中新世。通过对隐袋貂科牙齿形态的功能学分析，我们支持此前关于该类群为食谷性与/或食果性的推论。该新分类群所展现的演化阶段，与Namba组与Etadunna组的下部动物群带相当，这支持Pwerte Marnte Marnte化石组合的年代为渐新世晚期。