Koalas Had a Killer Cousin That Could Tear Prey Apart Like a Lion

Cuddly koalas are closely related to one of the deadliest mammals ever.

Australian folklore warns of the “drop bear,” a legendary and savage version of the koala said to leap from trees onto unsuspecting tourists. Now, scientists have found that the myth may have roots in the deep past.

A new study provides the first molecular evidence linking modern koalas to the long-extinct Thylacoleo carnifex, better known as the “marsupial lion,” one of the largest mammalian predators ever to stalk Ice Age Australia.

Led by Dr. Michael Buckley of the University of Manchester, the international team analyzed 51 fossilized marsupial bones collected from caves and swamps across Tasmania. The fossils, some more than 100,000 years old, were too ancient for DNA to survive. Instead, the researchers turned to collagen—the most durable protein in bone—using a cutting-edge method known as Zooarchaeology by Mass Spectrometry, or ZooMS.

“Until now, we’ve struggled to determine exactly how many of these extinct species were related because Australia’s hot climate destroys DNA over time,” Buckley explains.

“However, collagen proteins survive in much older and even extremely fragmented bones, allowing us to identify species and reconstruct the evolutionary relationships between extinct and living marsupials that could not be achieved through traditional methods.”

The Koala’s Menacing Cousin

The analysis shows that the tree-hugging koala and the bone-crushing Thylacoleo shared a common ancestor between 25 and 35 million years ago. That came as a major surprise, as the researchers expected the marsupial lion to be more closely related to wombats.

The two groups retained traces of shared ancestry, such as distinctive enamel ridges, before evolving in radically different directions—one toward carnivory, the other toward eucalyptus-munching herbivore.

The marsupial lion, which vanished around 40,000 years ago, was a muscular ambush predator about the size of a modern lion. It wielded scissor-like teeth capable of shearing flesh and enormous claws that could disembowel prey. Despite the differences in diet, Thylacoleo and the koala share some striking traits.

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“Anybody who’s actually cuddled a koala knows they are not nice animals,” Michael Archer, a paleontologist at the University of New South Wales, joked.

“They have gripping claws that can cause severe lacerations. Similarly, the tree-dwelling Thylacoleo was armed with huge, curved claws on its thumbs. When they grabbed prey and moved their hand around it, they would have unzipped the prey like a hot sausage,” he added during an interview with Science News.

Collagen Fingerprint

The same collagen sequences also helped decode the evolutionary positions of two other extinct megafauna: Zygomaturus trilobus, a wombat-like grazer weighing half a ton, and Palorchestes azael, a bizarre, tapir-nosed herbivore the size of a cow with rigid elbows and a long tongue. Both species, the study found, belonged to the same broad marsupial group as wombats and koalas, known as Vombatiformes.

By examining bones from seven Tasmanian sites—including Scotchtown Cave, Emu Cave, and the waterlogged Mowbray Swamp—the researchers demonstrated that collagen could persist far longer than DNA, even under challenging conditions. According to the paper, collagen was successfully extracted from bones as old as 100,000 years.

This discovery not only rewrites part of the marsupial family tree but also offers a powerful new tool for understanding prehistoric extinctions. During the Late Pleistocene, roughly 90 percent of Australia’s large land animals vanished—giant kangaroos, wombat-like Diprotodon, and the marsupial lion among them. The cause remains controversial: was it climate change, human hunting, or both?

By enabling identification of tiny, even fragmented fossils, collagen fingerprinting could finally clarify when and how Australia’s giants disappeared.

“ZooMS also allows thousands of fossil specimens to be analysed quickly, so it could be a game-changer for the study of extinct species,” Buckley said. “We can now identify more fossils, improve extinction chronologies, and better understand ancient biodiversity.”

As the authors write, collagen “offers great potential to better understand the diversity and evolution of past life on Earth.

Future studies may use the same approach to analyze even older or more degraded fossils, perhaps including the rhino-sized Diprotodon, the largest marsupial ever known.