Australia: The Land Where Time Began

A biography of the Australian continent 

Riversleigh Dasyurids 

Most of the Riversleigh dasyurids have lineages that don't appear to be represented among extant taxa, though some appear to be similar to taxa from the Kutjamarpu Local Fauna from the Tirari Desert. A species of dasyurid from the Oligocene-Miocene deposit at Riversleigh has been found to be an archaic dasyurid. It is believed to be near, or possibly on, the common stem of all later Antechinus of Australia and the Murexia of Australia and New Guinea. This find indicates that Antechinus and Murexia go back about 20 million years. All known Riversleigh dasyurids fit in the same size range modern species. It had been expected that at least some of the Riversleigh dasyurids would be larger, as occurs among mammal populations elsewhere. In fact, it seems the modern dasyurids are more diverse than those at Riversleigh. A suggested reason for this increase in diversity and size is that at Riversleigh they were competing with other carnivorous groups such as crocodiles, marsupial lions, snakes, and even carnivorous kangaroos.

An unexpected finding at Riversleigh has been that none of the animals of New Guinea are represented in its deposits. This finding was unexpected because the rainforests of New Guinea were believed to be refuge areas for Tertiary groups from Australia. Another unexpected finding was that the dasyurids of Riversleigh were less common in their habitat than many the small living representatives are in modern habitats. It has been suggested by Jeanette Muirhead that the lower population of dasyurids at Riversleigh may have been the result of competition with the very abundant and diverse peroryctid bandicoots, that were of similar size,  and that occurred in the same faunal assemblages, both searching for food on the floor of the Rainforest. The problem then becomes, why are the roles reversed in modern forests. Biodiversity of modern bandicoots is lower than that of dasyurids, while the biomass of bandicoots is much higher than that of dasyurids in many forests.

In the Riversleigh area, by the Pliocene the archaic dasyurids are not found and the modern genera such as Planigale and Sminthopsis are found. It is not known if the archaic groups persisted until later in other parts of Australia.

Sources & Further reading

Michael Archer, Suzanne J. Hand & Henk Godthelp, Australia's Lost World: Riversleigh, world heritage Site, Reed New Holland