Full Breakdown
Extinct “Dimpled” Koala Species Unveiled from Western Australian Fossils
5/6/2026, 11:32:16 AM
Discovery and Fossil Context
In 2024 the Western Australian Museum received a well-preserved koala skull from Moondyne Cave, donated by the family of caver Lindsay Hatcher. The skull, plus jaws, teeth and limb bones from Koala Cave (Yanchep), Foundation Cave (Margaret River) and Madura, prompted a reassessment of WA koala fossils collected since 1910. Researchers concluded the material represents a species distinct from the modern eastern koala, *Phascolarctos cinereus*.
Anatomical Distinctions
Measurements show a deep, rounded sulcus in the cheek of the upper jaw—absent in living koalas—and a shorter, more robust skull with broader teeth. The species, named *Phascolarctos sulcomaxillaris* (“grooved maxilla”), also has thinner long bones and a less elongated braincase, suggesting larger facial muscles and a different chewing strategy.
Dating and Extinction
Uranium–thorium dating places Margaret River specimens between 31 000 and 137 000 years old, Perth bones at ~75 000 years, and Madura material at ~24 000 years. Radiocarbon ages and pollen records indicate the species vanished around 28 000–30 000 years ago as south-west eucalyptus forests contracted during a prolonged cooling and drying phase.
Evolutionary Significance
The find raises the known koala count to four species, adding the extinct *P. sulcomaxillaris* to the giant Pleistocene *P. stirtoni* and the living *P. cinereus*. It shows that koalas once occupied a wider range and that isolated habitats can generate distinct lineages, highlighting the genus’ sensitivity to forest loss.
Official Statements
Kenny Travouillon, mammals curator at the Western Australian Museum, said the morphological differences “make it obvious” the fossils belong to a separate species. Tim Flannery of the Australian Museum called the study a “convincing case for the distinctiveness of the Western Australia koalas as a unique species.” The team plans further fieldwork to locate transitional fossils.
Conflicting Reports and Gaps
The extinction window is reported as both 28 000 and 30 000 years ago. While morphology strongly supports a separate species, the precise phylogenetic placement of *P. sulcomaxillaris* within *Phascolarctos* remains debated, with four species recognized but branching order unresolved. Additional central-Australian fossils could clarify these uncertainties.
Verbatim Quotes
- “The most striking feature is a deep, rounded sulcus (groove) in the cheek region of the upper jaw, below the eye socket.” — Kenny Travouillon, Western Australian Museum
- “The one feature that really made it obvious [it was a different species] was there was big grooves in the cheeks of the skull, like dimples,” — Kenny Travouillon, Western Australian Museum
- “There would have been [Tasmanian] devils, thylacines, giant echidnas, short-faced kangaroos and the giant marsupial Zygomaturus,” — Kenny Travouillon, Western Australian Museum
- “In combination with several distinct dental features and those bizarre concave sulci [cheek grooves] … it's definitely a different animal,” — Tim Churchill, University of New South Wales
What's Next
The team will test ancient DNA extraction from the fossils to refine phylogenetic placement and will survey South Australian caves for transitional specimens that could pinpoint when western and eastern koala lineages diverged.
