A Dimpled Koala Fossil Found in a Cave in Western Australia Revealed Why This Previously Unknown Species Went Extinct

The new study found that they lost their arboreal habitat due to a drying climate, a dire warning for the modern-day marsupials that face a similar threat

Sara Hashemi | Daily Correspondent

May 18, 2026 2:17 p.m.

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Beyond the kangaroos, wallabies and emus, Australia is famed for its iconic, seemingly cuddly koalas, even though the marsupials live only on the continent’s eastern and southeastern coasts.  About 28,000 years ago, the animals had a relative perching in trees on the west coast, but it was always thought to be of the same species (Phascolarctos cinereus) that lives today. Now, a new study published in the journal Royal Society Open Science on May 6 reveals that the region was actually home to a distinct koala species they named Phascolarctos sulcomaxilliaris.

The study began with a koala skull donated to the Western Australian Museum in 2024. It had been found in a cave in the town of Margaret River. Researchers at the museum noticed that the fossil had unusual characteristics—namely, dimples. No modern skulls in the museum’s collection had this feature. That “got us to start working on the fossil material in the collection,” says Kenny Travouillon, a study co-author and paleontologist at the museum, to James Woodford at New Scientist.

This led Travouillon and his colleagues to examine 98 bones from fossil specimens across the museum’s collection. They compared the fossils with modern koala skeletons using detailed skull and tooth measurements and other evolutionary analyses. They found that koala fossils from Western Australia differ significantly enough from their eastern counterparts to be a distinct species.

 “They had shorter heads, for sure, and they seem to have less-well-developed chewing muscles than the east-coast koalas,” says Travouillon to New Scientist. “But they simply chewed in a different way by having larger teeth and having a more efficient, shorter jaw to break down the leaves.”

Their bones were also thinner than modern koalas, he adds to Peter de Kruijff at the Australian Broadcasting Corporation. This suggests the koalas had less muscle and were possibly less agile. “So they spent less time moving between trees and stayed put as much as possible,” Travouillon explains.

To find out what happened to these dimpled koalas, researchers conducted uranium-thorium dating of the new fossils and radiocarbon dating of the others. This suggested that the animals likely went extinct about 28,000 years ago. This timing coincides with a major climate event that made Western Australia drier and colder, according to pollen records.

“Maybe there was some fires … and there's nothing for them to grow back with because there's not enough water in the system,” Travouillon says to ABC. “The forest disappeared.” Without food and shelter, the koalas went extinct.

Tim Flannery, a paleontologist at Sydney’s Australian Museum who was involved in the work, tells New Scientist that the study makes a “convincing case for the distinctiveness of the Western Australia koalas as a unique species.”

“I look forward to seeing if any DNA can be extracted from the fossils,” he adds.

The findings not only reshape the history of the koala, but it also underscores the importance of protecting forests for the animal’s conservation, the study authors write in a piece for The Conversation.

“The story of the [Western Australia] koala is a lesson learned to protect the last living koala species,” they write. “Protecting the eastern eucalypt forests from climate change and deforestation is paramount for the survival of koalas in the future.”

Sara Hashemi | Read More

Sara Hashemi is a science writer and fact-checker currently based in New York City. Her work has appeared in Sierra, The Body, Maisonneuve magazine and more.