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

WA Museum / Nellie Pease 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.