A 6-million-year-old fossil kangaroo from central Australia related to “cute and peculiar” wallabies on the island of New Guinea has allowed palaeontologists to build a picture of the connections between the landmasses’ ancient environments.
Cowpat Hill on Alcoota Station in the southern Northern Territory. Credit: Flinders University.
Kangaroos and wallabies are among Australia’s iconic animals. But the southern continent shares these unique creatures with its neighbour New Guinea.
Today, New Guinea hosts marsupials like the tree kangaroo, pademelon and possum. It even has an endemic species of echidna.
These links to Australia are a vestige of an ancient connection between the 2 landmasses.
New Guinea and Australia today are separated by the Torres Strait – just 160km apart at their closest point. During ice ages, huge amounts of water were locked up in Earth’s poles leading to sea levels more than 100m lower than today. In these periods, mainland Australia, New Guinea and Tasmania were all part of one landmass called Sahul.
The three sites the extinct species have been identified in Australia. Credit: Isaac Kerr (Flinders University).
Another type of animal shared by Australia and New Guinea is the wallaby.
A group of forest wallabies, called Dorcopsini, is today the only group of wallaby or kangaroo which is totally restricted to New Guinea. There are 6 living species of dorcopsin.
Patchy fossil evidence suggests that the ancient relatives of these “funny little wallabies” dispersed from Australia to New Guinea about 12 million years ago (mya) before vanishing from Australia about 5 mya for unknown reasons.
The Miocene epoch (23–5.3 mya) saw a global shift from a wetter, hotter climate to a dryer, cooler one. In Australia, this led to the thinning of forests and the emergence of the continent’s large swathes of desert.
Forest wallabies in New Guinea were spared this drying, clinging to the tropical forests which still persist on the island today.
“When the Torres Strait flooded again, however, these populations of animals became disconnected from their Australian relatives and so didn’t experience the dramatic drying-out that still defines much of Australia,” says Isaac Kerr, a palaeontologist from Flinders University in South Australia.
Kerr is lead investigator of a study published in the journal Alcheringa: An Australasian Journal of Palaeontology which describes a new species of extinct dorcopsin kangaroo which lived in the late Miocene.
Dorcopsoides cowpatensis was found at Cowpat Hill on Alcoota Station in the Northern Territory in central Australia, on the traditional lands of the Alywarre and Anmatjere Peoples.
Dorcopsoides cowpatensis shares many similarities with living forest wallabies but lived in a very different environment – dry, scrubby bush with widespread mallee and some dense woodland interspersed with seasonal creeks and lakes.
“This species is thought to have hopped swiftly, but only for short periods, moving from safer dense vegetation into more open areas to feed on leaves, fruits and fungi,” Kerr says.
Dorcopsoides cowpatensis is the third ancient member of the dorcopsin group found in Australia dating to the late Miocene and early Pleistocene (5.3 million to 11,700 years ago).
A modern white-striped dorcopsis in a zoo in Belgium. Credit: Melvin TOULLEC via Wikimedia Commons (CC BY-SA 4.0).
Modern forest wallabies are mysterious animals. Their diet and habitat remain uncertain.
“Living forest wallabies are cute and peculiar, with slightly sad, whippet-like faces,” says co-author Gavin Prideaux, also from Flinders. “Their strong, curved tails are used like a fifth limb during slow movement, much like in grey kangaroos, except that the tail arches so only the very tip touches the ground.”
The team is hopeful that further research of ancient and living wallabies will shed more light on the connections between New Guinea and Australia and also help science understand modern forest wallabies.
“Our research has taken us to Papua New Guinea (PNG) twice now and mid-last year we spent weeks digging out marsupial fossils along cliffs over the Watut River in eastern PNG,” says Kerr. “The university staff and local miners and villagers were immensely warm and friendly and helpful to us.
Flinders University palaeontologists, including Dr Isaac Kerr, front, are researching kangaroo fossils in Papua New Guinea. Credit: Flinders University.
“The experience demonstrated to me just how much our 2 nations have in common in the present day as much as in the prehistoric past.”