Paleontologists working at an undisclosed fossil bed in the Northern Territory's outback have discovered at least two new marsupial species including a wombat-like creature that could have weighed about 50 kilograms.
The discoveries were made at the roughly 25-million-year-old Pwerte Marnte Marnte site near Rainbow Valley, south of Alice Springs, which is thought to be one of Australia's oldest land mammal-bearing fossil beds.
The team from Flinders University with support from the Museum and Art Gallery of the Northern Territory made the discoveries recently.
PhD candidate Arthur Crichton, from Flinders University's Palaeontology Laboratory in Adelaide, visited the site as part of his research in 2020 and 2022.
"We've known about the site for a couple of decades," Mr Crichton said.
"It was found by chance in the early 2000s by a pair of horticulturalists walking along The Ghan railway line.
"They saw that some of the rocks had fossils in them. So they brought them to the NT museum."
The two species Mr Crichton has been involved in discovering and naming are Mukupirna fortidentata — a wombat-like creature and the Chunia pledgei, a distant relative of the modern-day possum.
The two species would have lived side-by-side during the late Oligocene — a geological epoch that started 28 million years ago and ended 23 million years ago.
The mammals would have been perfectly adapted to Central Australia's then climate — a much wetter and forested environment.
The research team has had papers published in both the Journal of Vertebrate Paleontology and Alcheringa: An Australasian Journal of Palaeontology
"The Mukupirnids are thought to be the group most closely related to modern wombats, being a bit of an evolutionary intermediate between wombats and their more koala-like relatives," Mr Crichton said.
"It's not really correct to say that Mukupirna is an ancestral wombat either. It seems to have gone off on its own evolutionary tangent that is very much unique in the context of marsupial evolution."
Mr Crichton said researchers believe the Mukupirna became extinct sometime before the end of the late Oligocene — roughly 23 million years ago.
At the site, the team found several fragments of skeletal remains that were from different individual animals.
"We found a partial skull and several partial lower jaws," he said.
"We also found half a dozen other bones including half a humerus, half a tibia, two tali — that's one of the weight-bearing bones in the foot and a bunch of isolated teeth."
The skull and teeth have provided some clues about the ancient mammal and what they ate.
"Intriguingly, the molars are actually pretty similar to those of some monkeys, such as macaques.
"But the front teeth are very large, and spike-shaped, a bit like a rodent's.
"It would have had a pretty powerful bite, well suited to processing hard plant material."
It is thought that the Mukupirna could have weighed about 50 kilograms making it one of the larger marsupials of the time.
'Dentist's nightmare'
Mr Crichton said that in comparison to the 35 specimens of the Mukupirna, the team only found three specimens of the Chunia pledgei, the modern-day possum relative.
"That may not sound like a significant number but they are tantalisingly rare to find in the fossil record," he said.
"A number of the species have been named from one fossilised tooth."
Mr Crichton said they found a lower jaw with four teeth intact.
"We also found half an upper molar and a small molar fragment — only a sixteenth of a tooth."
He said the shape and complexity of structures on the teeth could be likened to a barcode in that each species has a unique set.
"Chunia pledgei had teeth that are a dentist's nightmare with lots of bladed cups that are positioned side by side," he said.
"They've got lots of cusps with crests that are parallel with one another."
He said not much was known about the now-extinct marsupial which belonged to the family Ektopodontidae.
"We know that these animals had a lemur-like short face with particularly large forward-facing eyes but until a more complete skeletal material is found, their ecology will remain mysterious."
He said the find puts the evolution of animal groups we have around today into a broader context.
"Part of it is a real sense of intrigue of what Australia was like 25 million years ago.
"But ektopodontids also really underpin that the iconic marsupials we have today are just a small sample of the amazing and globally unique animals that once existed."
