New material of the toothed platypus Obdurodon insignis (Monotremata: Ornithorhynchidae) from the late Oligocene Pinpa Local Fauna at Billeroo Creek, South Australia

Monotreme fossils of pre-Pliocene Cenozoic age are very rare in Australia and limited to those of the toothed platypus Obdurodon (Ornithorhynchidae). From the late Oligocene fluvio-lacustrine sediments of central Australia, the record includes only three teeth, a partial dentary and a partial ilium, all assigned to Obdurodon insignis Woodburne and Tedford, 1975. Here, we report three more fossils attributed to O. insignis: a lower first molar; an upper second premolar; and a partial scapulocoracoid from the Namba Formation exposed at Billeroo Creek, Frome Downs Station, South Australia, which contribute to the Pinpa Local Fauna that is of late Oligocene age. The scapulocoracoid is only the second postcranial element referred to a species of Obdurodon. It shows this fossil platypus had a very similar pectoral girdle to the modern Platypus Ornithorhynchus anatinus (Shaw, 1799), which along with the general skull morphology of another ancient platypus, Obdurodon dicksoni Archer et al., 1992, suggests that the general form of the extant Platypus has existed since at least the late Oligocene.