Quarter ton marsupials roam long distances across arid Australia

One of Australia’s first long-distance walkers has been described after Flinders University paleontologists used advanced 3D scanning and other technology to view the partial remains of a 3.5 million year old marsupial from central Australia.

They named the new genus diprotodontid Outpatientmeaning walker or wanderer, because the adaptations to the locomotor and foot movements of this quarter-tonne animal made it suitable for exploring long distances in search of food and water when compared to its earlier relatives.

Researcher says skeleton outpatient, discovered at the Australian Wildlife Conservation Reserve’s Kalamurina Station in northern South Australia by Flinders University researchers in 2017, belongs to a species in the family Diprotodontidae, a group of four-legged herbivores that were the largest marsupials ever.

“Diprotodontids are very distantly related to wombats – the same distance kangaroos are to possums – so sadly there is nothing like them today. As a result, paleontologists have a hard time reconstructing their biology,” says Jacob van Zoelen, PhD candidate in Flinders University’s Laboratory of Paleontology.

largest Species, Diprotodon chose, growing to the size of a car, weighing up to 2.7 tons. Diprotodontids were an integral part of the Australian ecosystem until the last species went extinct around 40,000 years ago.

During the period when outpatient keana (Pliocene), there was an increase in grassland and open habitat as Australia became drier. Diprotodontids likely had to travel much greater distances to get enough food and water to survive.

“We don’t often think of walking as a specific skill, but if you are big any movement can use up a lot of energy, so efficiency is key,” says Mr van Zoelen.

“Most of today’s large herbivores such as elephants and rhinos are digitigrade, meaning they walk on their toes with their heels off the ground.

“Diprotodontids are what we call plantigrade, meaning their heel bone (calcaneus) hits the ground when they walk, similar to how humans do. This stance helps distribute weight while walking but uses up more energy for other activities like running.”

The diprotodontids displayed extreme plantigrad in their hands too, by modifying the wrist bone, the pisiform, into a secondary heel, explains Mr van Zoelen.

This ‘heeled hand’ made the animals’ early reconstructions look strange and awkward, he said.

“The development of the wrists and ankles for weight bearing means that the toes are essentially nonfunctional and likely do not touch the ground when walking. This is probably why no finger or toe prints were observed in diprotodontid tracks.

“So, diprotodontids are like Outpatient may have developed this morphology to traverse great distances more efficiently. This morphology also allows for greater weight support, allowing diprotodontids to be very large.

“Eventually, this led to a gigantic and relatively well-known evolution Diprotodon.”

Most studies in the group have focused on skulls, because related skeletons are rare in the fossil record. Thus, this newly described framework is of great importance and is even more special because it is the first to be discovered with associated soft tissue structures.

Using 3D scanning technology, Flinders’ team was able to compare the partial skeleton with other diprotodontid materials from collections around the world.

Wrapping around an individual’s leg is hard concrete that forms shortly after death. With a CT scan of the specimen, impressions of the soft tissue that maintains the sole of the foot are revealed.

Note to editors: The specimen has been 3D scanned and the file is now free available for anyone to download and view online. They will also be included in the Virtual Australian Museum of Palaeontology (VAMP), which researchers and Flinders Palaeontology colleagues will launch on 1 June 2023.

New article, Redescription of Pliocene marsupials outpatient keana comb. november (Diprotodontidae) from outback Australia and its locomotive adaptation (2023) by Jacob D van Zoelen, Aaron B Camens, Trevor H Worthy and Gavin J Prideaux has been published in Journal of Royal Society Open Science DOI: 10.1098/rsos.230211

https://dx.doi.org/10.1098/rsos.230211

Thank-you note: This research was funded by the Australian Government Research Training Program Scholarship (Excellence). Trips to the collection are funded in part by the small grants scheme of the Royal Society of South Australia 2018, University of California Museum of Palaeontology Doris O. and Samuel P. Welles Fund 2019, Flinders University Higher Degree Research International Conference Travel Grant 2019 and North America Conference Student Travel Grants Paleontology. For assistance on the ground at Kalamurina Station, we thank Tess McLaren and Keith Bellchambers from the Australian Wildlife Conservancy.