“Strange” fossil kangaroo, leads to new genus unique to Papua New Guinea

End of the New Guinean megafauna. Artist’s impression of Nombe Rockshelter prehistoric animals showing the large kangaroo (renamed Nombe Nombe), on left. Illustration courtesy Peter Shouten

A “strange” primitive kangaroo has been classified as a new species, unique to Papua New Guinea, in the peer-reviewed journal, Transactions of the Royal Society of South Australia.

Fossil and jaw bones found in the in the remote highlands of Papua New Guinea in the 1970s, have been re-analyzed by Australian palaeontologists from Flinders University. Their findings show that rather than being closely related to Australian kangaroos, it most likely belongs to a unique genus of more primitive kangaroo found only in PNG.

The kangaroo, first described in 1983 by Professor Tim Flannery, is known from fossils around 20,000-50,000 years old. They come from the Nombe Rockshelter, an archaeological and palaeontological site in Chimbu Province, Papua New Guinea.

Nombe is already known for multiple extinct species of kangaroo and giant four-legged marsupials called diprotodontids.

Flinders University researchers have renamed the animal Nombe nombe, after the location of its discovery – and plan to return to PNG for further excavations and research next year.

The squat, muscular Nombe lived in a diverse montane rainforest with thick undergrowth and a closed canopy. Here, it evolved to eat the tough leaves from trees and shrubs, with a thick jaw bone and strong chewing muscles.

The species is estimated to have grown to between 40 and 50 kilograms – just slightly less than today’s commonly found eastern grey kangaroo (Macropus giganteus).

Much of the animal life of New Guinea is little-known outside of the island, despite its colour and distinctiveness. This discovery breathes some new life into the exploration of New Guinea’s faunal history.

“The New Guinean fauna is fascinating, but very few Australians have much of an idea of what’s actually there,” says 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.

“We think of these animals as being uniquely Australian, but they have this intriguing other life within New Guinea.”

Using 3D imagery and other technology, the researchers have studied remains from the PNG Museum and Art gallery. They now believe that the species may have evolved from an ancient form of kangaroo that dispersed into New Guinea in the late Miocene epoch, around 5-8 million years ago.

During that time, the islands of New Guinea and mainland Australia were connected by a ‘land-bridge’ due to lower sea levels, rather than separated by the flooded Torres Strait as they are today. This ‘bridge’ allowed early Australian mammals, including various giant, extinct forms, to move into the rainforests of New Guinea.

When the Torres Strait flooded again, however, these populations of animals became disconnected from their Australian relatives, and so evolved separately to suit their tropical, mountainous PNG home.

Nombe is now considered the descendant of one of these ancient lineages of kangaroos.

However, Kerr says: “This strange kangaroo was not a species of the genus Protemnodon, which used to live all over Australia, from the Kimberley to Tasmania. It was something a lot more primitive and unknown.

“In particular, its unusual molars with curved enamel crests set it apart from all other known kangaroos.”

Sporadic palaeontological work was undertaken there by American and Australian researchers in the 1960s, ‘70s and ‘80s, much of which resulted in fascinating discoveries of extinct megafauna. However, no palaeontological digs have taken place there since the early ‘90s, a situation the Flinders University researchers seek to remedy.

Co-author on the new Royal Society article, Flinders University Professor Gavin Prideaux, says the research will expand thanks to a grant from the Australia Pacific Science Foundation.

“We’re very excited to undertake three palaeontological digs at two different sites in eastern and central PNG over the next three years,” he says.

“We’ll be working with the curators of the Papua New Guinea Museum and Art Gallery and other contacts in PNG, with whom we hope to build some local interest in New Guinean palaeontology.”

The species is currently only known from two fossil lower jaws. Much more remains to be discovered.

“Did Nombe hop like modern kangaroos? Why did it go extinct?,” asks Kerr.  “As is typical of palaeontology, one discovery inspires an entire host of new questions.”