Ancient kangaroo species from Papua New Guinea jumps into view

Australia has very distinctive animals and plants. From the plethora of eucalypts and colourful parrots to the marsupials that bound and climb through the Aussie bush, it can appear like a different planet to those living in different parts of the world.

Well, almost. There is one place which shares a lot of the unique wildlife of the sunburnt country: Papua New Guinea.

Australia and PNG were once connected by the Sahul land bridge, submerged by what is now Torres Strait about 8,000 years ago. But before PNG was separated from the Australian mainland, the two lands shared very similar ecosystems. Even today, marsupial tree kangaroos and long-beaked echidnas roam in PNG’s forests.

Archaeologists and palaeontologists found in the remote mountains of PNG signs of even more familiar forms in fossils from the island. After sporadic scientific work in the 1960s, ’70s and ’80s on prehistoric PNG fauna, one specimen has been recently reclassified, signalling a new species of ancient kangaroo in PNG unlike anything alive in Australia today.

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The research was published by Australian palaeontologists from Adelaide’s Flinders University in the Transactions of the Royal Society of South Australia. The new description shows that, rather than being closely related to its Australian cousins, the fossil kangaroo most likely belongs to a unique, primitive genus found only in PNG.

The kangaroo was first described in 1983 by Professor Tim Flannery. The fossils, dating back to 20,000-50,000 years ago, were found in the Nombe Rockshelter in Chimbu Province. Nombe is home to multiple extinct species of kangaroo and giant four-legged marsupials called diprotodontids.

The kangaroo has been renamed Nombe nombe, after the site. Nombe would have been a large, squat, muscular animal. It lived in montane rainforest with thick undergrowth and a closed canopy where it ate tough leaves with its thick jawbone and strong chewing muscles.

The researchers note that much of New Guinea’s animal life is little known outside the island. “The New Guinean fauna is fascinating, but very few Australians have much of an idea of what’s actually there,” says co-author and Flinders palaeontology PhD candidate Isaac Kerr.

“There are several species of large, long-nosed, worm-eating echidna that are still around today, many different wallaby and possum species that we don’t get in Australia, and more still in the fossil record,” Kerr adds. “We think of these animals as being uniquely Australian, but they have this intriguing other life within New Guinea.”

“Nombe Rockshelter is in central PNG, around 300-400km to the east of the centre of the island. It’s a rugged, mountainous area,” explains Kerr. “It would have been quite a bit colder than it is now – maybe about six degrees colder – but still very high rainfall.”

Kerr paints a picture of the upper montane forest through which Nombe would have hopped. The forest would have been more dense, with shorter trees than today. Sharing many of the Australian bush’s flora, the ancient PNG forest would have had eucalypts and casuarina trees as well as tall beech trees and a dense undergrowth of big ferns.

Apart from the extant echidnas, wallabies and possums, PNG was home to other familiar animals. “There would have been these other large kangaroos from a genus called Protemnodon, which is what Nombe was considered to be before this study,” Kerr adds.

Other megafauna sharing the ancient PNG forests were Hulitherium and Maokopia – large quadrupedal herbivores the size of big pigs.

Kerr and his colleagues studied Nombe’s remains from the PNG National Museum and Art Gallery. Using 3D imagery, the researchers were able to analyse the remains without having to visit.

“Photos can only do so much,” says Kerr. “We needed a way to be able to look at the fossils without being there with them. So we got this fancy 3D scanner and you put the bone on a turntable. As it spins, the scanner looks at all the different sides and pieces together this 3D image of the surface. From that, you can do measurements and render images.”

While not as detailed as an in-person study, the scanner can capture detail as small as 200 microns, while avoiding damaging the fossil by exposing it to moisture and the atmosphere for extended periods.

From the scans, the researchers were able to determine that the fossil is from a kangaroo not closely related to living kangaroos in Australia. “It’s surprising that this kangaroo is so different from ‘modern’ kangaroos. The closest common ancestor with those kangaroos is around eight million years ago,” says Kerr.

Kerr says the discovery highlights the huge scope for further discoveries in PNG.

“No one’s been there to look for fossils in over 25 years,” Kerr says. “There’s something like seven megafaunal species known from there, which is not many at all. There’s reason to believe that the megafauna in New Guinea was less diverse than Australia’s, so we’re not expecting to find as many species as we have in Australia. But there’s almost certainly a lot more species there that we don’t know about yet.”

“We’re very excited to undertake three palaeontological digs at two different sites in eastern and central PNG over the next three years,” says co-author Gavin Prideaux, professor at Flinders University. “We’ll be working with the curators of the PNG National Museum and Art Gallery and other contacts in PNG, with whom we hope to build some local interest in New Guinean palaeontology.”