DUAL ORIGIN FOR AUSTRALIA'S PLEISTOCENE REPTILIAN FAUNA: EVIDENCE FOR A LATE CRETACEOUS DISPERSAL FROM ANTARCTICA

Until recently, giant horned turtles (Family Meiolaniidae) have only been known to come from the Eocene (50 mya) of Argentina and the Pleistocene (2 mya to 10,000 ya) of Australia. The dispersal to account for this disjunct distribution of the meiolaniid turtles has been hypothesized as a northern route from South America up through North America to Asia and then to Australia after Australia had "docked" with southeast Asia in the Pliocene. In the final dispersal phase from Asia to Australia, meiolaniid turtles would have immigrated into Australia along with murid rodents, varanid lizards and elapid snakes. A specimen representing apart of the anterior carapace of a meiolaniid turtle was found by one of us (DAC) in Unit B of the Etadunna Formation (latest Oligocene, ca. 25 mya), at Lake Palankarinna, South Australia. This specimen is added to a small, but growing, list of Late Oligocene to Late Miocene meiolaniid specimens recovered from inland localities in Australia. These same localities have expanded the record of reptilian taxa, which have traditionally been regarded as Plio-Pleistocene immigrants from Asia into Australia. The more recent findings of meiolaniid specimens earlier than the Pleistocene, including the Late Cretaceous of Argentina, indicate that meiolaniids occurred earlier in Australia, when that continent was completely isolated in the southern IndoPacific Ocean. From these earlier occurrences of horned turtles in Australia and Argentina, a new biogeographic hypothesis can be formed. The horned turtles would disperse from Argentina through Antarctica to Australia, traveling "a southern route", and excluding the original "northern route" hypothesis. This more recent distribution of meiolaniid taxa in time and space, coincides with the dispersal trackway of marsupials, ratite birds, chelid turtles and madtsoiid snakes into Australia in the latest Cretaceous and a reverse migration of monotreme mammals from Australia to Argentina in this same time period.