Australia: The Land Where Time Began

A biography of the Australian continent 

Riversleigh Pygmy-Possums-burramyids

There are 2 basic types of Pygmy-possums living, the genus Circartetus, the size of a large mouse, and the Mountain Pygmy possum, Burramys parvus, that is a bit bigger. The Mountain Pygmy possum is highly specialised, living in the alps of southeastern New South Wales and northern Victoria.

B. triradiatus was discovered in the Hamilton Local Fauna from the Early Pliocene of Victoria. At the time of deposition, this site was a lowland rainforest in western Victoria. Another species of Burramys has been found to be plentiful in the deposits from the Oligocene-Miocene at Riversleigh. Another species, B wakefieldi, has been found in the Ngama Local Fauna from the Miocene of central Australia.

A surprise in the history of pygmy possums is that the Burramys, regarded as more specialised than the other possum group, has been found in earlier deposits than the less-specialised Cercartetus-tpye burramyids.

A third family of possums, the Pilkipildridae, has been found in Oligocene-Miocene deposits in central Australia. A Cercartetus-type taxon has been found at Riversleigh that appears to be a distant relative of C. caudatus, a modern inhabitant of rainforests of northeastern Australia and New Guinea.

As the forests were drying out and retreating, at some point the ancestral pygmy possums must have moved to a lifestyle in keeping with the increasing seasonality of their environment during the Late Pliocene and Early Pleistocene, becoming more centred on the rocky terrain underlying the forests they had previously inhabited. This was probably when the ancestors of the living species began to hoard food for winter. It is believed that by the time the upland rainforests had been replaced by sclerophyll woodland the ancestral possums had already switched to spending part of each year hidden among rocks. The living species spend several months during the winter in rock piles in the ranges, often buried under a layer of snow.

Sources & Further reading

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