This Marsupial Lion Was the Size of a Squirrel

The ancient carnivore is one of two new pouched mammals recently discovered based on fossil teeth and jaws.

Vinegar is a handy liquid to have around. You can use it to clean your computer mouse, wipe down your blinds, and remove carpet stains. Or, even better, you can use it to discover some seriously cool extinct animals.

Acetic acid—one of vinegar’s main constituents—is commonly used as a chemical treatment to unlock delicate fossils from their rocky shackles. Recently, paleontologists in a remote corner of Australia used the procedure to extract the teeth of two long-dead mammal species from blocks of limestone.

Though the teeth are the only remains of the newly discovered species, we can glean plenty of details from a set of chompers. As paleontologist Steve Wroe says, “you can get a hell of a lot of information from a single tooth!”

For starters, one fossil jaw turned out to be a new addition to a bizarre family of meat-eating mammals called the marsupial lions. But unlike its previously discovered cousins, the new pouched creature was exceptionally tiny, coming in at about the size of a grey squirrel.

“This animal was just so small—it’s quite extraordinary,” says Anna Gillespie, the University of New South Wales paleontologist who found and identified the new species. “To me, it’s quite stunning.”

Teeny-Tiny Jaws of Steel

Marsupial lions belong to an extinct prehistoric family that is most closely related to modern koalas and wombats. The family currently includes nine species, and its most famous member is Thylacoleo carnifex.

Thylacoleo, which roamed what is now Australia as recently as 46,000 years ago, is known for its extremely powerful bite: Pound for pound, its jaws packed more force than a modern lion or hyena bite.

The new addition to the family, Microleo attenboroughi, was named in honor of the renowned naturalist David Attenborough. It is a diminutive version of T. carnifex that lived around 18 million years ago, according to the study published in the July edition of Palaeontologia Electronica. Weighing in at approximately 1.3 pounds (600 grams), Microleo was considerably smaller than its 220-pound (100-kilogram) relative.

Gillespie and her team identified the species using parts of its jaw recovered from limestone deposits at the Riversleigh World Heritage Area, a famous fossil site in Australia.

The fossilized teeth became exposed through the millennia as water slowly dissolved the limestone surrounding them. A volunteer found a portion of the tooth protruding from a rock block, and it was fully freed when Gillespie used the acetic acid to eat away the remaining limestone.

Teeth are commonly used to identify species, especially mammals, says Wroe, a paleontologist at the University of New England in Australia who was not involved in the study. The shapes of the teeth, in particular, can reveal what the animal most likely ate and other clues to how it fit into its ancient ecosystem.

“The molar teeth are typically more informative than other teeth because they are more complex,” he says. Based on its teeth—premolars and molars from both the left and right jaw—Microleo was probably an arboreal predator that dined on a variety of other small creatures.

“It was likely living up in the trees having a good time and eating all the small animals,” Gillespie says.

For now, though, the team still has plenty of unanswered questions, because the teeth that Gillespie found are the only evidence that this Lilliputian carnivore ever existed. This could indicate the species was rare when it lived, or it could just mean Gillespie and her team need to keep looking for additional fossils, which is no problem for the self-described discovery junkie.

“I just find it really intriguing that this is the only specimen we have,” she says. “You just want to go out and find more, and keep looking and looking. To get a skull would be fabulous.”

King of Beasts

The other pearly white pulled from Australian limestone belonged to another new marsupial species: Whollydooleya tomnpatrichorum. The genus name references the site of the find—Wholly Dooley Hill—and the species name is a shout-out to longtime Riversleigh researchers Tom and Pat Rich.

Michael Archer, a National Geographic grant recipient, worked with Gillespie, her Microleo co-author Suzanne Hand, and others to describe the new marsupial in the Memoirs of Museum Victoria.

While Microleo was unique for being petite, Whollydooleya stands out for its extreme dentition, specifically, its blade-like teeth.

While the team found only one tooth, its shape indicates the animal was a hypercarnivore—a flesh-eating creature whose diet consisted of at least 75 percent meat. The raised points on the crown, known as primary cusps, are interspersed with shearing enamel blades, a feature that, according to Wroe, is only useful for cutting meat.

To Archer, the tooth’s form also suggests that the creature would have been safe from bad breath: Their distinct shape would have effectively cleared out rotting food particles that can cause halitosis.

Whoolydooleya, which lived about 12 million to five million years ago, was placed in the Dasyuridae family, which includes over 60 species of mostly small and mouse-like marsupials, including the Tasmanian devil.

However, Archer says that the new species represents a group of carnivorous marsupials that were not previously known. The researchers estimate that Whoolydooleya was about 50 pounds (23 kilograms), or two to three times the size of the modern Tasmanian devil. With its nasty teeth and large frame, Archer believes it would have been a formidable opponent.

“It probably would have been the ‘king of beasts’ within its home range,” he writes, “able to catch and gobble pretty much any other animal that took its fancy.”

However, Whoolydooleya would not have been dining on Microleo, as the two species are separated by millions of years. Still, looking at both fossil animals together can tell the researchers a lot about changes in Australia’s ancient climate.

Neville’s Garden, the site of the Microleo find, contains stalagmites preserved in fossil material and is believed to have been a cave pool in a rich, diverse rain forest environment.

But the younger sediments at Wholly Dolly Hill suggest that the hypercarnivore was buried during a drier time. Combined, the fossils corroborate the theory that Australia transitioned from a wet, humid climate to its arid state during the Miocene.

As scientists find more fossils around Riversleigh—particularly other small to medium-size animals—they will be able to further piece together what was happening as Australia dried out. Figuring out how life responded to a changing ancient climate is essential to helping us understand modern extinctions, especially in the face of accelerated climate change.

As Archer notes, we don’t know what caused Microleo and Whollydooleya to go extinct, but “climate change … has always been the primary reason for extinctions.”

Follow Aaron Sidder on Twitter.

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