A strange giant kangaroo roamed New Guinea's highland forests long ago, up until the end of the last ice age.
Now, research by me and colleagues suggests that this kangaroo was not closely related to modern Australian kangaroos. Rather, it is a previously unknown primitive kangaroo unique to New Guinea.
The age of megafauna
Bis to the time when most of the megafauna disappeared, Australia used to be home to all kinds of giant animals, including kangaroos, koalas, crocodiles, and the like, but many were larger species.
Phascolonus, 2.5-metre-long short-faced kangaroos, and the 3-tonne Diprotodon optatum (the largest marsupial ever) are among the oldest Australian megafaunal animals. Such as the red kangaroo, emu, and cassowary, these animals have survived until today.
New Guinea's fossil megafauna are considerably less well-studied than those of Australia. However, the fossil record of New Guinea has revealed some fascinating and unusual animals whose evolutionary histories overlap with Australia's.
Paleontologists have conducted occasional excursions and fossil excavations in New Guinea, including excavations by American and Australian researchers in the 1960s, 1970s, and 1980s.
Two jaws of an extinct giant kangaroo were discovered during an archaeological excavation in the early 1970s, led by Mary-Jane Mountain. A young researcher (now professor) named Tim Flannery named the species Protemnodon nombe.
Flannery's fossils are some 20,000 million years old. They were collected at the Nombe Rockshelter, an archaeological and palaeontological site in the highlands of Central Papua New Guinea. Another kangaroo and giant four-legged marsupials were discovered at this site.
A surprise discovery
Professor Gavin Prideaux and I recently re-examined the fossils of Protemnodon nombe and discovered something surprising. This strange kangaroo was not a species of the genus Protemnodon, which used to inhabit Australia from the Kimberley to Tasmania. It was something far more primitive and unknown.
The unusual molars with curving enamel crests set it apart from all other known kangaroos. We renamed the species Nombe nombe (very creatively).
Nombe may have evolved from an ancient kangaroo that migrated into New Guinea from Australia during the late Miocene period, some 58 million years ago.
Due to lower sea levels, the islands of New Guinea and Australia were linked by a land bridge, while today they are separated by the Torres Strait.
This "bridge" enabled early Australian mammals, including megafauna, to migrate to New Guinea's rainforests. When the Torres Strait flooded again, these animal populations became disconnected from their Australian relatives and evolved separately to suit their tropical and mountainous surroundings.
Nombe is thought to be the descendant of one of these ancient kangaroo lineages. It evolved to eat tough leaves from trees and shrubs, giving it a strong jawbone and robust chewing muscles.
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?
One discovery sparks a whole host of new questions, as is typical of paleontology.
Strange but familiar animals
Outside the island, little is known about New Guinea's endemic animal life, which is both strange and fascinating. Very few Australians have much of an understanding of what's there, just across the river.
I was pleasantly surprised by the animals I encountered at the Papua New Guinea Museum early in my PhD project. There are a number of large, long-nosed, worm-eating echidna species, one of which weighs up to 15 kilograms.
There are also dwarf cassowaries and many different wallaby, tree kangaroo, and possum species that aren't native to Australia, as well as many others in the fossil record.
These animals are a lot of fun to watch, but there are also many other interesting forms in New Guinea.
It's both odd and thrilling to see these "Aussie" animals evolve into new and strange forms in a different environment as a biologist.
N. nombe may bring some new life to paleontology in New Guinea, according to me and my colleagues. We're part of a small group of researchers that was recently awarded a contract to undertake three excavations at two different sites in eastern and central Papua New Guinea over the next three years.
We hope to incite young local biology students to investigate paleontology and discover new fossil species. If we're lucky, there may even be a complete skeleton of Nombe nombe waiting for us.
Isaac Alan Robert Kerr, PhD Candidate for Paleontology at Flinders University.
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