How a Changing Climate May Have Killed Off the Marsupial Lion

Deep in the Australian Outback, the locals will tell you, a legendary beast roams the bush, preying on the unprepared and the unawares. This mythical creature, the drop bear, is a ravenous variant of the koala that has developed a taste for flesh rather than leaves. And while the drop bear itself doesn’t exist, it does have a real-life counterpart in a predatory marsupial of the past.

Over 46,000 years ago, Australia was home to Thylacoleo, a distant cousin of wombats, kangaroos and other marsupials. But unique among this subclass of mammals, Thylacoleo preyed on other animals for its food, and so paleontologists know the ancient creature as the “marsupial lion.”

But why doesn’t this impressive carnivore still prowl the Australian wilds? A new analysis of the predator’s teeth, carried out by Vanderbilt University paleontologist Larisa DeSantis and presented at the Society of Vertebrate Paleontology annual meeting last month, offers some new clues.

“The initial aim of this study was to figure out the paleobiology of this animal,” DeSantis says. Despite being known to scientists since 1859 and having various studies of its anatomy carried out, relatively little is known about how this predator hunted, ate its prey and otherwise interacted with its surrounding environment. It turns out, the marsupial lion’s teeth were key to solving some of these mysteries.

The cheek teeth of Thylacoleo are very distinctive. They are more square than triangular, having the appearance of meat cleavers that slid past each other to shear through flesh. Pits and scratches on the teeth, called microwear, are tied to different foods and feeding behaviors that can help narrow down the animal's diet. DeSantis also looked at stable isotope signatures—a version of “you are what you eat,” DeSantis says, in which chemical signatures from particular food sources get taken up and preserved in tissues like teeth and bone.

It turns out that Thylacoleo lived up to its name. The microwear on the analyzed fossil teeth showed damage patterns most similar to modern-day lions. Translating this to diet, it means that Thylacoleo didn’t avoid chewing on bone as assiduously as cheetahs do, but it wasn’t a bone-crusher like the spotted hyena. Thylacoleo came out somewhere in between, mostly preferring to feed on flesh but sometimes chewing on—or through—the bones of its prey.

“People tended to see it as ‘big, bad carnivore, can eat anything it wants,’” says Brown University paleontologist Christine Janis. “This analysis confirms that it was more of a selective meat eater, and probably not much of a scavenger.”

Based upon the isotope data and other lines of evidence, such as where Thylacoleo bones have been found with other fossils, DeSantis also hypothesizes that this carnivore was an ambush predator that preferred relatively wooded environments, offering plenty of cover. In the old forests of Australia, Thylacoleo could stalk ancient, giant kangaroos like Protemnodon.

The trouble for the predator all started when climate change altered the local habitat. What drove some of Australia’s megafauna to extinction is a fiercely-debated question (just as it is with Ice Age extinctions elsewhere around the world). Some experts place the blame on newly-arrived humans, who hunted and used fire to clear the landscape, killing off many large and iconic species. Others point to climate change, noting dramatic shifts that, in this case, made Australia much more arid and denuded forests that many species relied upon.

If DeSantis and her team are correct that Thylacoleo relied on the forest for cover to stalk its prey, then the desertification of Australia would have stripped away the marsupial lion’s cover, leading to its demise.

“I think that climate is more important than people have been thinking. The extreme aridity of present-day Australia is probably relatively recent,” Janis says. More desert-like conditions altered Australia from about 300,000 years ago onward.

Given what we now know about the diet of Thylacoleo and its preferred habitat, harsh climate shifts made all the difference for this carnivore. “It’s an ambush hunter, it’s eating prey from these forests, it’s postcranial anatomy indicates its pouncing from trees or some sort of cover,” DeSantis says, and the loss of forest cover would have directly affected this carnivore’s ability to pounce upon its preferred prey, not to mention that there would be less prey to stalk in these environments. “With aridification, this animal was particularly vulnerable to extinction,” DeSantis says.

The tale of this lost predator may have lessons for today, as dramatic climate shifts driven by humans continue to alter habitats around the world. Thylacoleo, the real drop bear of history, likely won't be the last apex hunter to fall along with its environment.

Riley Black | | READ MORE

Riley Black is the author of The Last Days of the Dinosaurs and many other books. She is a science correspondent for Smithsonian magazine covering fossils and natural history, and she writes about the prehistoric past for a variety of publications.