Previously unexamined fossil specimens housed within the Western Australian Museum have been definitively identified as a novel species of koala. This ancient creature, christened Phascolarctos sulcomaxilliaris, ceased to inhabit Western Australia subsequent to climatic shifts marked by arid conditions and falling temperatures, which dramatically altered its ecological niche towards the close of the Pleistocene epoch.
Reconstruction of Phascolarctos sulcomaxilliaris. Image credit: Nellie Pease.
The contemporary koala (Phascolarctos cinereus) stands as Australia’s largest living arboreal herbivore and represents one of the nation’s most recognizable marsupial icons.
Koalas are presently found across a spectrum of woodland environments along Australia’s eastern seaboard, and have been successfully introduced to various locales in South Australia, including areas proximate to Adelaide and Kangaroo Island.
This species is currently designated as Vulnerable by the IUCN, having experienced significant population reductions over time due to factors such as habitat destruction, prevalent diseases, vehicular collisions, predation by domestic dogs, and historical hunting for its pelts.
“Although koalas are now regionally extinct in Western Australia (WA), their fossilized remains have been documented since 1910,” stated Dr. Kenny Travouillon, a distinguished researcher affiliated with both the Western Australian Museum and Curtin University, alongside his colleagues.
“Bones were previously unearthed from multiple cave formations in the southwestern region of WA, including Koala Cave in Yanchep and Madura Cave situated on the Roe Plain.”
“Given the anatomical similarities observed in their dentition to those of Phascolarctos cinereus, these specimens were traditionally presumed to belong to the same species.”
In their comprehensive investigation, the paleontological team meticulously analyzed 98 skeletal elements sourced from fossilized specimens within the Western Australian Museum’s archives.
Cranial structures, dentition, and postcranial remains were systematically compared against modern koala skeletons curated in museum collections situated on Australia’s eastern continent.
The findings revealed distinct and measurable divergences between the fossilized specimens from WA and their contemporary counterparts from the east, thereby substantiating the existence of a new species, officially designated Phascolarctos sulcomaxilliaris.
“This newly identified species exhibits several remarkable characteristics that distinguish it from extant koalas,” commented Dr. Travouillon.
“Profound sulci present within the zygomatic bone are believed to have accommodated substantial musculature of the face, suggesting this animal may have possessed exceptionally large, mobile lips. These adaptations could have facilitated more adept manipulation of eucalyptus foliage, or perhaps served to flare its nostrils, thereby amplifying its olfactory capabilities to detect sustenance from considerably greater distances.”
“Its skeletal structure was likely less flexible compared to that of modern koalas, implying it may have dedicated less temporal investment to arboreal locomotion between trees.”
Fossil evidence of Phascolarctos sulcomaxilliaris has now been identified across more than a dozen subterranean deposit sites throughout southern Western Australia, encompassing locations such as Yanchep, Margaret River, and the Roe Plain in proximity to Madura.
This extensive geographical distribution indicates that these primitive koalas once inhabited a geographical range far more expansive than previously understood.
Radiometric dating methodologies have established that Phascolarctos sulcomaxilliaris met its demise approximately 28,000 years prior.
“This temporal correlation aligns with a significant climatic upheaval during the Late Pleistocene epoch, a period characterized by the contraction of eucalyptus forests to a mere 5% of their contemporary coverage,” explained Dr. Travouillon.
“With drastic reductions in both food availability and shelter, koalas inhabiting this region likely confronted severe habitat degradation, ultimately precipitating the extinction of this unique lineage.”
A scholarly publication detailing the characteristics of Phascolarctos sulcomaxilliaris was released today in the journal Royal Society Open Science.
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Kenny Travouillon et al. 2026. New fossil koala (Marsupialia: Phascolarctidae) from the Pleistocene of Western Australia. R Soc Open Sci 13 (5): 251572; doi: 10.1098/rsos.251572
