Researchers at the Western Australia Museum have identified a new extinct species of koala, known as the WA or dimpled koala (Phascolarctos sulcomaxilliaris), based on unique features observed in skulls discovered in the region. These koalas thrived in eucalypt forests until approximately 28,000 years ago, when a significant climatic shift led to the destruction of their habitat.
This newly recognized species is the only one native to Western Australia, apart from modern koalas (Phascolarctos cinereus) that were introduced to conservation areas and wildlife parks in Perth over the last century. Analysis of two donated skulls, now housed at the WA Museum Boola Bardip, prompted the identification of the dimpled koala, with notable differences from contemporary koalas becoming evident through detailed comparisons.
According to Kenny Travouillon, the museum’s curator of mammals, the most distinctive characteristic of the dimpled koala is the pronounced grooves in its cheekbones, which resemble dimples. “No modern koala skulls exhibited these dimples,” Dr. Travouillon remarked, suggesting that these anatomical features could have facilitated greater facial muscle development.
In a study published in Royal Society Open Science, Dr. Travouillon and his colleagues proposed that the unique structure of the dimpled koala’s skull might have enhanced its ability to detect food through larger lips or flared nostrils. Their research also involved a reassessment of previously collected koala bones from the area, concluding that all belonged to this newly identified species, indicating that modern koalas never resided on the west coast except for those recently introduced.
The skulls, which were provided by the family of the late Lindsay Hatcher, a caver from Margaret River, also offer insights into the species’ dietary habits and cognitive abilities. Dr. Travouillon noted that while the dimpled koala was similar in size to modern koalas, it exhibited several anatomical differences, potentially indicating lower cognitive functions. He stated, “This species lacks the elongated back of the brain case seen in modern koalas, suggesting it may have been less intelligent.”
Furthermore, the dimpled koala likely had adaptations that allowed it to chew eucalyptus leaves more efficiently due to its wider teeth and distinct jaw angle, which facilitated quicker consumption. Dr. Travouillon also observed that the bones of the dimpled koala were thinner than those of modern koalas, implying reduced muscle mass and agility, which may have led it to spend more time stationary rather than moving between trees.
Tim Churchill, a palaeontologist from the University of New South Wales who was not involved in the study, commented on the robustness of the dimpled koala’s skull, highlighting its unique dental characteristics and the distinctive cheek grooves as evidence of its divergence from other koala species. He speculated that these features might indicate a greater reliance on smell compared to sound.
Modern koalas represent the last surviving members of the genus Phascolarctos, which is believed to have emerged around five million years ago. While the exact number of species within this genus remains debated, it is generally accepted that it includes both the dimpled and contemporary koalas. The geographic isolation of WA’s dimpled koalas may have arisen as Australia experienced drying climates and retreating forests during their evolutionary history.
The fossilized remains of the dimpled koala have been discovered in various caves across Western Australia, including locations in Perth, Margaret River, and Madura near the South Australian border. Uranium-thorium dating conducted by the University of Queensland estimates the ages of these bones, revealing ranges from 31,000 to 137,000 years for those found in Margaret River, approximately 75,000 years for Perth, and around 24,000 years for the younger fossils from Madura.
During the period leading to the extinction of the dimpled koala, the southwest of WA experienced significant climatic changes, including a marked reduction in rainfall, as indicated by local pollen records. Dr. Travouillon noted that the loss of forests likely resulted from these climatic shifts, which may have included fires that further devastated the ecosystem. Although reforestation began about 10,000 years later, it likely came too late to save the dimpled koala from extinction.
