Academic literature on the topic 'Diprotodontoidea'

Abstract We describe the partial cranium and skeleton of a new diprotodontian marsupial from the late Oligocene (~26–25 Ma) Namba Formation of South Australia. This is one of the oldest Australian marsupial fossils known from an associated skeleton and it reveals previously unsuspected morphological diversity within Vombatiformes, the clade that includes wombats (Vombatidae), koalas (Phascolarctidae) and several extinct families. Several aspects of the skull and teeth of the new taxon, which we refer to a new family, are intermediate between members of the fossil family Wynyardiidae and wombats. Its postcranial skeleton exhibits features associated with scratch-digging, but it is unlikely to have been a true burrower. Body mass estimates based on postcranial dimensions range between 143 and 171 kg, suggesting that it was ~5 times larger than living wombats. Phylogenetic analysis based on 79 craniodental and 20 postcranial characters places the new taxon as sister to vombatids, with which it forms the superfamily Vombatoidea as defined here. It suggests that the highly derived vombatids evolved from wynyardiid-like ancestors, and that scratch-digging adaptations evolved in vombatoids prior to the appearance of the ever-growing (hypselodont) molars that are a characteristic feature of all post-Miocene vombatids. Ancestral state reconstructions on our preferred phylogeny suggest that bunolophodont molars are plesiomorphic for vombatiforms, with full lophodonty (characteristic of diprotodontoids) evolving from a selenodont morphology that was retained by phascolarctids and ilariids, and wynyardiids and vombatoids retaining an intermediate selenolophodont condition. There appear to have been at least six independent acquisitions of very large (>100 kg) body size within Vombatiformes, several having already occurred by the late Oligocene.

The extinct diprotodontoids were large bodied, browsing herbivorous marsupials most closely related to, among living marsupials, wombats. Referred to two families, Diprotodontidae and Palorchestidae, diprotodontoids are geographically and temporally widespread vombatimorphian taxa in Australian and New Guinean Cenozoic deposits. The most diverse diprotodontoid fauna recorded from any single region in Australia comes from Oligo-Miocene limestone deposits of the Riversleigh World Heritage Area, northwestern Queensland. In this thesis a new diprotodontoid genus and five new species are described from Riversleigh, as well as additional material from Riversleigh for the palorchestids Propalorchestes novaculacephalus and Pr. ponticulus and diprotodontids Nimbadon lavarackorum, Neohelos tirarensis, Neohelos stirtoni and Ngapakaldia bonythoni. A new vombatomorphian family, Maradidae, known from a single species at Riversleigh, is recognised as the sister-group of a vombatid-diprotodontoid clade. New abundant, exceptionally well-preserved cranial material of the zygomaturine Nimbadon lavarackorum enables characterisation of intraspecific variation and ontogenetic development. The results of these analyses have been used to discriminate species boundaries throughout this work. Consequently: Nimbadon whitelawi is now considered a junior synonym of Ni. lavarackorum; Nimbadon scottorrorum is a junior synonym of Neohelos tirarensis; and Bematherium angulum is a synonym of Ngapakaldia bonythoni. The new Riversleigh diprotodontoids clarify phylogenetic relationships within and between diprotodontoid families. The monophyly of both Palorchestidae and Diprotodontidae is strongly supported as is their union in the superfamily Diprotodontoidea. Monophyly of the Zygomaturinae and Diprotodontinae is not supported, primarily due to the unstable position of Alkwertatherium webbi as well as the high degree of homoplasy in cranial morphology of the more derived members of each subfamily. Overall phylogenetic and distribution patterns for diprotodontoids is generally consistent with current interpretations of Riversleigh's stratigraphy. Five diprotodontoid species allow direct biocorrelation with other Australian Tertiary mammal faunas. Riversleigh's basal System A deposits correlate with late Oligocene deposits of the Etadunna Formation of South Australia. Riversleigh's low-mid System C deposits correlate with the middle Miocene Bullock Creek Local Fauna of the Northern Territory. Riversleigh's high System C Jaw Junction and Encore Local Faunas contain diprotodontoid taxa antecedent to diprotodontoids of the late Miocene Alcoota Local Fauna of the Northern Territory.