A PRELIMINARY study has been carried out on fossil remains (unearthed in the British Museum) from a travertine deposit in Tasmania. Regardless of the precise taxonomic assignments ultimately given to this material, the evidence we present that a diverse fauna of diprotodont marsupials existed in Australia in late Oligocene time is of considerable importance. This evidence gives tangible support to the hypothesis that marsupials have been residents of the Australian continent since the early Tertiary at least. The basic differentiation of herbivorous Diprotodonta from Marsupicarnivora (Ride, 1964) very likely took place before the separation of Australia from Antarctica. By late Oligocene time Tasmania was situated near 52°S latitude¹ bathed by warmer seas² and the travertine accumulated in an equable warm–temperate to subtropical environment supporting a rich forest vegetation^3–5 the closest living equivalents of which occur in the uplands of New Guinea and New Caledonia. Present-day representatives of some of the fossil marsupials from the travertine still inhabit such tropical environments in northern Australia and New Guinea.