Paleontologists have redescribed an extinct species of giant kangaroo that lived the mountains of Papua New Guinea about 50,000 to 20,000 years ago and erected a new genus for it.
An artist’s impression of Nombe nombe (right) and other prehistoric animals from Nombe Rockshelter, Papua New Guinea. Image credit: Peter Shouten.
The large mountainous island of New Guinea forms the northern portion of the Australian continent and is home to a varied and unique marsupial fauna, including numerous endemic genera and species.
Kangaroos and their close relatives (family Macropodidae) are represented in the modern New Guinean fauna by multiple species of tree-kangaroos (genus Dendrolagus), pademelons (Thylogale), dorcopsises (Dorcopsis and Dorcopsulus), as well as the spectacled hare-wallaby (Lagorchestes conspicillatus) and the agile wallaby (Notamacropus agilis).
No modern New Guinean macropodids exceed 20 kg in adult body mass, but several larger-bodied fossil species are known: Protemnodon nombe, Protemnodon hopei, Protemnodon tumbuna, and Dendrolagus noibano.
“The New Guinean fauna is fascinating, but very few Australians have much of an idea of what’s actually there,” said Isaac Kerr, a Ph.D. candidate at Flinders University.
“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.”
As part of the review of the Protemnodon genus, Kerr and his colleague, Flinders University’s Professor Gavin Prideaux, focused on Protemnodon nombe, which was first described in 1983 on the basis of two partial jaws from Nombe Rockshelter, Papua New Guinea.
They found that the species differed from other members of the genus in several ways and should be classified as a separate genus, Nombe.
“Now known as Nombe nombe, this kangaroo lived in a diverse montane rainforest with thick undergrowth and a closed canopy,” the researchers said.
“It evolved to eat the tough leaves from trees and shrubs, with a thick jaw bone and strong chewing muscles.”
The authors believe that Nombe nombe evolved from an ancient form of kangaroo that dispersed into New Guinea during 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,” they explained.
“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 Papua New Guinea home.”
“Nombe nombe is now considered the descendant of one of these ancient lineages of kangaroos.”
The findings were published in the journal Transactions of the Royal Society of South Australia.
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Isaac A.R. Kerr & Gavin J. Prideaux. A new genus of kangaroo (Marsupialia, Macropodidae) from the Late Pleistocene of Papua New Guinea. Transactions of the Royal Society of South Australia, published online June 29, 2022; doi: 10.1080/03721426.2022.2086518
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