Limb osteology and functional morphology of the extinct kangaroo Dorcopsoides fossilis (Macropodinae, Marsupialia) from Late Miocene central Australia

The 'modern' kangaroos and wallabies (subfamily Macropodinae) are herbivorous marsupials characterized by their bipedal hopping gait. Macropodines radiated through the Late Miocene and Pliocene (11.6-2.6 Ma) as Australia aridified. Dorcopsoides fossilis, known only from the Late Miocene Alcoota locality in central Australia, is the earliest undisputed macropodine. Although first described in 1967 from craniodental and postcranial fragments, it has since received minimal attention, despite the accumulation of many more specimens and the potential they hold for shedding light on kangaroo evolution. Here we describe its limb morphology and make comparisons with limb bones of extant species with various locomotory modes and habitat preferences. Though D. fossilis is generally similar to living low-geared hoppers, it has certain features seen in higher-geared macropodines that imply some ability to hop powerfully and efficiently. These features indicate the species was adapted to moving through open habitats, consistent with past interpretations of the Alcoota palaeoenvironment. As in modern macropodines, the pronounced size bimodality in forelimb elements of D. fossilis likely represents sexual dimorphism. Our results strongly reinforce the macropodine affinity of D. fossilis, demonstrating that the dominant features of the macropodine skeletal plan were in place well before the end of the Miocene.