Giant Extinct Wombat Relative Like Nothing Paleontologists Have Seen Before

Mukupirna is an extinct animal the size of a bear whose closest living relatives are wombats and koalas, but is as different from each as those to are from each other. Peter Schouten

A skull and skeleton found in South Australia's Flinders Range came from a creature related to wombats and koalas, but different enough it has been given its own taxonomic family. The discovery helps illuminate the poorly understood early evolution of Australia's most beloved creatures.

The only living Vombatiformes are koalas and three species of wombats. These are sufficiently different from each other that Professor Mike Archer of the University of New South Wales told IFLScience they are considered separate families. Vombatiformes were once far more abundant and diverse, with members as different from the living animals as wombats and koalas are from each other, leading to their classification as being in distinct families. The most famous of these are the diprotodonts, some of which weighed three tonnes and dominated the Australian ecosystem as recently as 50,000 years ago.

To this list a Scientific Reports paper has added Mukupirna, weighing in at 143-171 kilograms (315-380 pounds). Only one confirmed specimen has been found, dating from 25 million years ago, but it is unusually complete. Archer told IFLScience several less well-preserved fossils from Riversleigh may also belong to this family.

Aside from its bear-like size, Mukupirna looks more recognizably like a wombat than some Vombatiformes, such as the carnivorous marsupial lion. However, Archer said its distinctive teeth demonstrate that this creature deserves its own family. Although its arms were well suited to digging, it is thought not to have been capable of wombats' remarkable digging feats. Instead, it probably fed on roots and tubers scratched from the ground.

Cranium in ventral view. Robin Beck et al.

Archer told IFLScience Mukupirna is not ancestral to modern wombats and koalas; we have specimens of their closer ancestors from around the same time. However, the Australian fossil record is so sparse between 50 and 25 million years ago that we lack anything much older, so we don't know how the different Vombatiformes families separated.

Mukupirna means “big bones” in the languages of the Dieri and Malyangapa peoples, whose lands include the dry salt lake where Archer helped find the fossil in 1973. In a statement, he attributed this to luck.

“In most years the surface of this dry lake is covered by sands blown or washed in from the surrounding hills. But because of rare environmental conditions prior to our arrival that year, the fossil-rich clay deposits were fully exposed to view. On the surface, and just below, we found skulls, teeth, bones and in some cases, articulated skeletons of many new and exotic kinds of mammals. As well, there were the teeth of extinct lungfish, skeletons of bony fish and the bones of many kinds of water birds including flamingos and ducks.”

Archer added to IFLScience: “We knew we had something big [with Mukupirna], but we didn't know what it was.”

The fossil was sent to the American Museum of Natural History for the clay to be carefully removed, a project that took 17 years. Once this happened, Archer and Richard Tedford realized they had something unique and planned to investigate it together. However, Tedford died shortly after, and Archer focused on other things. Decades later, Archer's former student Dr Robin Beck of the University of Salford noticed the specimen at the museum and contacted Archer to collaborate, unaware the man he was contacting had helped dig it from the ground almost 40 years before.

“Koalas and wombats are amazing animals,” said Beck, “but animals like Mukupirna show that their extinct relatives were even more extraordinary, and many of them were giants.”

“Australian paleontology is at an equivalent stage to North America in the 1800s,” Archer said to IFLScience. “There are such large gaps in the fossil record it's not a big surprise when we scratch the surface and find something distinctively different.”

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