The illustration shows a reconstruction of one of the early Miocene species of koala, which was similar to the modern species in many respects but smaller in size.
Credit: Dorothy Dunphy
SYDNEY: Ancient koalas may have enjoyed a much more diverse diet than today’s koalas, but were probably just as loud and lazy as their modern cousins.
A team led by Julien Louys, a palaeontologist at the University of New South Wales (UNSW) in Sydney, compared skull fragments of two fossil species – Litokoala kutjamarpensis and Nimiokoala greystanesi – to the one living species.
Both prehistoric marsupials lived about 20 million years ago. They have been known about for many years, but researchers have only recently collected enough cranial fossil material from the Riversleigh World Heritage Site in Queensland to make the study possible.
Different diet
The new research, published in the current Journal of Vertebrate Palaeontology, showed there were significant differences in the teeth, palate and jaws of prehistoric koalas compared to modern koalas (Phascolarctos cinereus), but the remainder of the skulls were similar.
The experts said that the unique shape of the modern koala skull is a result of accommodating changes to the way koalas eat without compromising the way they hear.
UNSW palaeontologist Mike Archer said there is an intimate relationship between eating and hearing in mammals, because the jaw is immediately adjacent the ear and because mammalian ear bones are descended from ancestral jaw bones.
Jaw and ear
“It’s not uncommon to see changes in jaw structure impacting on the ability to hear,” he said. “But in this case [the changes] don’t appear to have had that impact.”
Louys said that over time the koala underwent substantial changes to its facial bones. The changes allowed koalas to chew with greater force to cope with a new diet consisting entirely of tough eucalyptus leaves, which are low in nutritional content and have high levels of tannins.
Archer said that it is probable the prehistoric koalas either had a more diverse plant diet, possibly avoiding eucalyptus altogether, or lived on species of eucalypts whose leaves were not as hard to eat as the leaves of eucalypts today. Australia then drifted north, causing its rainforests to retreat to northern refuges and eucalypts to become the dominant tree in most Australian forests.
