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

Abstract

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 reidentified 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. http://zoobank.org/urn:lsid:zoobank.org:pub:8881FF3A-4B9F-4085-A5C2-1BBF976CFB65 SUPPLEMENTAL DATA-Supplemental materials are available for this article for free at www.tandfonline.com/UJVP.

A probable koala from the Oligocene of central Australia provides insights into early diprotodontian evolution

“…Relationships and divergence estimates for extant lineages follow Duchêne et al 6 . Those of extinct lineages follow Beck et al 5 , Travouillon et al 102 , and Crichton et al 38 , 39 . The divergence estimates for extinct vombatiforms and phalangeroids are speculatory.…”

“…It is less clear how metatherian stylar cusp homologies translate to the somewhat bunolophodont molars of thylacoleonids and most early phalangeriforms (Fig. 7 ; see 5 , 36 , 38 , 64 and references therein). Thylacoleonids have been interpreted, by some, as retaining the symplesiomorphic condition of a continuous centrocrista and a distinct stylar shelf 38 , 65 , 66 .…”

“…7 ; see 5 , 36 , 38 , 64 and references therein). Thylacoleonids have been interpreted, by some, as retaining the symplesiomorphic condition of a continuous centrocrista and a distinct stylar shelf 38 , 65 , 66 . It has also been suggested that that the small buccal-most structures on the M1 of thylacoleonids are actually neomorphic, and that the primary buccal cusps, traditionally referred to as the paracone and metacone, are actually stylar in origin 5 .…”

“…Local Fauna, and Age . Initial biochronological assessments have suggested that the Pwerte Marnte Marnte LF is late Oligocene age 38 , 39 , 48 , and may predate the oldest late Oligocene assemblages from the Etadunna and Namba Formations of the southern Lake Eyre Basin, perhaps corresponding to an as-yet-unnamed land mammal age immediately preceding the Etadunnan 29 , 48 .…”

New fossils, new ideas: selected contributions of vertebrate paleontology to scientific knowledge

“…Among the latter, the ektopodontids are a rare group of marsupials so far only recorded in Australia from Oligocene to Pleistocene outcrops. In “A new ektopodontid possum (Diprotodontia, Ektopodontidae) from the Oligocene of central Australia, and its implications for phalangeroid interrelationships” Arthur I. Crichton and coauthors (2023) describe a new species that leads them to analyze the phylogenetic relationships of all phalangeroid possums using morphological and molecular data. Considering the results of their phylogenetic analyses and the high morphological diversity that phalangeroids had already attained by the late Oligocene, they conclude that the group must have had an extensive evolutionary history that predates their earliest records and has yet to be discovered.…”