A long-neglected fossil in the Western Australian Museum’s collection has been identified as a new species of koala, named Phascolarctus sulcomaxiliaris. This ancient animal vanished from Western Australia as drought and cooling transformed its habitat at the end of the Pleistocene epoch.
Comparatively, the modern koala (Phascolarctus cinereus) is Australia’s largest arboreal folivorous creature and serves as one of the continent’s most iconic marsupials.
Koalas inhabit various forest types along Australia’s east coast and have also migrated to parts of South Australia, including Adelaide and Kangaroo Island.
These remarkable animals are currently listed as vulnerable. Historically, their populations have faced declines due to habitat destruction, disease, vehicle strikes, predation by dogs, and hunting for fur, according to the IUCN.
“Although the koala is now locally extinct in Western Australia (WA), its remains have been known since 1910,” stated Dr. Kenny Trabouillon from the Western Australian Museum and Curtin University.
“Bones attributed to this species have previously been reported from several cave deposits in southwestern WA, including Koala Cave at Yanchep and Madura Cave on the Low Plains.”
Due to similarities in their teeth, Phascolarctus cinereus and the new species were historically considered the same.
In their study, paleontologists analyzed 98 bones from fossil specimens in the Western Australian Museum’s collection.
They compared the skulls, teeth, and posterior skulls to modern koala skeletons housed in museum collections along Australia’s east coast, revealing distinct and quantifiable differences that characterized Phascolarctus sulcomaxiliaris.
“This species exhibits several notable distinctions from contemporary koalas,” Dr. Trabouillon noted.
“The presence of large facial muscles in deep grooves of the cheekbones suggests that this koala may have possessed unusually large and flexible lips, potentially useful for manipulating eucalyptus leaves or enhancing its sense of smell to detect food from afar.”
Additionally, it appears that its skeletal structure was less agile than that of modern koalas, indicating it may have spent less time traversing trees.
Fossils of Phascolarctus sulcomaxiliaris have now been found across more than a dozen locations in southern Western Australia, including Yanchep, Margaret River, and the Low Plains near Madura.
This extensive distribution suggests that these koalas once occupied a significantly larger range than previously understood.
Radiometric dating indicates that Phascolarctus sulcomaxiliaris became extinct around 28,000 years ago.
“This timing coincided with significant climate change during the Late Pleistocene, when eucalyptus forests were reduced to about 5% of their current coverage,” explained Dr. Trabouillon.
“With substantial loss of food and shelter, the koalas in this region faced severe habitat degradation, likely leading to the extinction of this unique species.”
A detailed paper describing Phascolarctus sulcomaxiliaris has been published in today’s edition of Royal Society Open Science.
_____
Kenny Trabouillon et al. 2026. A new fossil of a Pleistocene koala (Marsupial: Phascolarctidae) from Western Australia. R Soc Open Science 13 (5): 251572; doi: 10.1098/rsos.251572
Source: www.sci.news
