A new species of Miocene wombat (Marsupialia, Vombatiformes) from Riversleigh, Queensland, Australia, and implications for the evolutionary history of the Vombatidae

Abstract

A new species of wombat, Rhizophascolonus ngangaba sp. nov., is described from Miocene deposits at Riversleigh along with additional specimens of Rhizo-phascolonus crowcrofti, and some maxillary and mandibular fragments attributable to Rhizophascolonus. A phylogenetic analysis indicates that Rhizophascolonus is the next most plesiomorphic wombat after Nimbavombatus boodjamullensis. Morphological characters common to Nimbavombatus and Rhizophascolonus suggest that adaptations to high rates of tooth wear in wombats had their origin in the late Oligocene, presumably in response to climatic cooling and its effects on the vegetation. A period of climatic amelioration in the early Miocene may have led to diversification of wombats and/or to an expansion of their range into rainforest habitats. Although wombats form a significant component of Australia's open-forest and woodland habitats from the early Pliocene to Holocene, they appear to have been rare in all palaeoenvironments prior to this.