Ancient koala fossils fill gap in Australian marsupial history

Fossils of an ancient koala relative have added another piece to the puzzle of how Australia’s unique marsupials evolved.

Lumakoala blackae weighed roughly 2.5 kg – about the size of a small domestic cat. Scientists who discovered this new species believe that its diet would have consisted mostly of soft leaves, “but wouldn’t have turned down an insect given the chance.”

The ancient marsupial is described in a paper published today in Science Advances.

It is known from fossilised molars collected in 2014 and analysed in 2020. Lumakoala blackae was discovered at the Pwerte Marnte Marnte fossil site in Australia’s Northern Territory. The site dates to 25 million years ago during a period of Earth’s history known as the Oligocene epoch (roughly 34 million to 23 million years ago).

During the Oligocene, Australia would have been much wetter with much of what is now the central deserts of the continent being covered by forest and wetland.

Palaeontologists believe Lumakoala blackae can help illuminate what happened during a 30-million-year gap in Australia’s marsupial fossil record.

Only two fossil sites have yielded mammal fossils in Australia dating between 110 million and 25 million years ago and virtually nothing is known about mammalian evolution on the continent between 55–25 million years ago.

“Our computer analysis of its evolutionary relationships indicates that Lumakoala is a member of the koala family (Phascolarctidae) or a close relative, but it also resembles several much older fossil marsupials called Thylacotinga and Chulpasia from the 55-million-year-old Tingamarra site in northeastern Australia,” says first author Arthur Crichton, a PhD student at Adelaide’s Flinders University.

“This group (Diprotodontia)is extremely diverse today, but nothing is known about the first half of their evolution due to a long gap in the fossil record,” Crichton adds.

“In the past, it was suggested the enigmatic Thylacotinga and Chulpasia may have been closely related to marsupials from South America. However, the discovery of Lumakoala suggests that Thylacotinga and Chulpasia could actually be early relatives of Australian herbivorous marsupials such as koalas, wombats, kangaroos and possums.”

Another two species of koala were found at the site.

“Until now, there’s been no record of koalas ever being in the Northern Territory; now there are three different species from a single fossil site,” says Professor Gavin Prideaux, director of the Flinders University Palaeontology Laboratory.

Prideaux describes the late Oligocene as a “kind of the koala heyday.”

“While we have only one koala species today, we now know there were at least seven known from the late Oligocene – along with giant koala-like marsupials called ilariids. These were the largest marsupials in Australia at the time, weighing in at up to 200 kg.”