Marlu

Abstract: The first unique genus of ringtail possums from the Riversleigh World Heritage Area in Australia is diagnosed and described. Gawinga aranaea is the type and only species of the new genus and is known from nine isolated lower molars. It has been recovered from three Riversleigh deposits: two are of early to mid-Miocene age, while the age of the other has yet to be determined. The new possum is larger than Oligo-Miocene species of Paljara, Pildra, and Marlu, but smaller than most extant taxa. It is characterised by a distinctive lower molar cusp morphology of parallel ridges extending primarily from the cristid obliqua, filling the occlusal basins. Additional autapomorphies include: extended, shelflike protostylid cristids and a bisected posthypocristid on m1, and posterior molars that have a metaconid ridge posterobuccal to the metaconid and an anteriorly positioned protoconid relative to the metaconid. It also possesses an enlarged protostylid on m1, a feature otherwise known only in extant genera. The precise phylogenetic position of Gawinga within the pseudocheirid radiation has yet to be determined, but it is tentatively identified here to be a highly derived pseudocheirid, apomorphic with respect to Paljara and Pildra species, and with no known descendants.

Abstract: Four genera of extinct ringtail possums have been reported from Australian Oligocene to Miocene sediments since 1987. The genus Marlu was described from two species, M. kutjamarpensis and M. praecursor (Woodburne, Tedford and Archer), from the Miocene Kutjamarpu Local Fauna (Leaf Locality) and late Oligocene Wadikali Local Fauna respectively, of northern South Australia. New fossil material referable to this genus has been collected from the Leaf Locality and the Oligocene to Miocene Riversleigh World Heritage Area in northwest Queensland. Three new species, Marlu karya sp. nov. from middle Miocene Riversleigh local faunas and Marlu syke sp. nov. and Marlu ampelos sp. nov. from the Leaf Locality as well as early to middle Miocene Riversleigh local faunas are described. A revision and rediagnosis of the genus and published species are made following the re-examination of referred material in conjunction with the new material. Marlu is characterized by simple dentition and synapomorphies with extant pseudocheirids such as a conjoined postmetacristid and preentocristid on m1 and the loss of the entostylid ridge. New material from middle Miocene Riversleigh deposits has been referred to M. kutjamarpensis, extending the known distribution and age of that species. Re-examination of M. praecursor has revealed the presence of a small m1 entostylid ridge, contributing further to differences between M. praecursor and all other Marlu species and raising the possibility that Marlu is paraphyletic. The new material does not contradict a sister group relationship between ‘Marlu’ (excluding M. praecursor) and the Pliocene–Pleistocene genus Pseudokoala. Homology of the pseudocheirid m1 protostylid identified in species of Paljara, Pildra and Marlu with that observed in extant species is reconsidered. The ‘protostylid’ of the extinct genera is herein described as the buccal stylid.