New species couldn't hop, but outlived its fanged kangaroo contemporaries

Lead author Kaylene Butler of UQ's School of Earth Sciences said the new kangaroo species were discovered in ancient fossil deposits at the Riversleigh World Heritage Area in north-western Queensland, Australia.

"They lived around 15-23 million years ago and were the size of very small wallabies or pademelons," she said.

"They moved on all fours, scurrying across a densely forested landscape quite different from the dry outback we see in western Queensland today.

"It also appears that our new species were direct competitors with a second group of kangaroos at Riversleigh, the even weirder 'balbarid' or fanged kangaroos.

"It seems likely that the fanged cousins were out-competed by our new species and their descendants."

The new species may have been better adapted than their fanged cousins to the environmental change from rainforest to more open forest and woodland environments. They are described in the Journal of Vertebrate Paleontology.

Ms Butler worked on fossil material as part of her PhD research supervised by study co-authors former UQ Robert Day Fellow, Dr Kenny Travouillon, now of Western Australian Museum, and Dr Gilbert Price of UQ.

Riversleigh research leaders Professors Michael Archer and Suzanne Hand, of the University of New South Wales, are also study authors.

She said that by taking measurements and comparing skulls and teeth with known species, it was discovered that they were looking at both a new genus (taxonomic rank) and two new species within the genus.

She said the new genus was named Cookeroo, in honour of Dr Bernard Cooke, a distinguished Queensland Museum researcher who led much of the research program focused on the evolution of Riversleigh's ancient kangaroos.

The two new species within the genus are Cookeroo bulwidarri, which lived about 23 million years ago, and Cookeroo hortusensis which lived 20 million to 18 million years ago.

Bulwidarri means "white" in the Aboriginal Waanyi language, and is named for White Hunter Site at the Riversleigh World Heritage Area where specimens of this species were obtained. Hortusensis is Latin for "belonging to the garden," in reference to Neville's Garden Site at Riversleigh where specimens of this species were found.