Data from: New fossil koala (Marsupialia: Phascolarctidae) from the Pleistocene of Western Australia

Fossils of koalas have been known from Western Australia since 1910, but
are today regionally extinct. Jaws and bones were previously reported from
several cave deposits in the south-west of WA, Koala Cave in Yanchep, and
from Madura Cave on the Roe Plain. Due to the similarity of the dentition
with the east coast koalas (Phascolarctos cinereus), they were
traditionally assumed to be the same species. Two complete additional
adult skulls were collected in the past 25 years. These skulls are
interpreted to belong to a male and female koala, are similar in body size
to koalas from Victoria, but the shape of the skulls differ significantly,
in being relatively much shorter in length, and having obvious deep
concavities on the maxilla, below the zygomatic arch. Differences from the
eastern species are also apparent in the postcranial skeleton. Analysis of
measurements on the skulls and teeth show that the Western Australian
koala is morphologically distinct from its east coast relative and
warrants consideration as its own species. It likely went extinct in WA as
a result of climate change during the late Pleistocene, which reduced
eucalyptus forests to around 5% of their current cover, reducing resources
for food and shelter.