Analysis of Riversleigh fossils has revealed fascinating new facts about a tiny possum's ancestors.

Scientists have long known that the miniature feather-tailed possums in Australia and the island of New Guinea-members of the marsupial family Acrobatidae-were evolutionary cousins, but where they started their long evolutionary journey has been a bit of a mystery-until now.

According to recently published research in Alcheringa: An Australasian Journal of Palaeontology, paleontologists from UNSW Sydney say the modern-day animals on either side of the Torres Strait came from common ancestors in Australia before diverging into their living gliding and non-gliding descendants, known as Acrobates pygmaeus in Australia and Distoechurus pennatus in New Guinea.

"Not only did we find two new species related to the Australian feathertail gliders, the species of Acrobates, but more surprisingly, two new species related to the New Guinean modern-day feather-tailed possum, Distoechurus pennatus." This confirms, says Fabian, that the Distoechurus possums didn't originate in New Guinea as was once thought, they actually originated in Australia before moving north to New Guinea.

For one thing, says co-author Emeritus Professor Suzanne Hand, New Guinea was largely underwater.

"What we're seeing is that ancestors of these animals are turning up in Riversleigh rainforests before the birth of modern day New Guinea," Hand says.

"Prior to the discovery of this fossil record in Australia, many zoologists assumed that these groups, which are more diverse in New Guinea, originated there before spreading south to invade Australia. It has made us rethink our whole understanding of how these animals got to where we find them today." Gliding doors moment Climate change and a gradual drying of mainland Australia from about 15 million years ago is said to be the factor that led to some Australian possums evolving gliding as an adaptation to the changing environment.