The discovery of a missing branch of the koala family tree has shed light on the evolution of the iconic marsupial.
The Lumakoala, which lived about 25 million years ago and was about the size of a domestic cat, has filled a knowledge gap in the evolution of its drop bear ancestor.
Flinders University PhD student Arthur Crichton found the ancient animal's fossilised teeth in central Australia and led the study confirming its relation to modern-day koalas.
"The new species ... probably ate mostly soft leaves but wouldn’t have turned down an insect given the chance," he said.
He says the Lumakoala resembles 55 million-year-old fossils of marsupials Thylacotinga and Chulpasia, which suggests the older animals were also related to koalas as well as fellow diprotodons possums, wombats and kangaroos.
"If our hypothesis is correct, it would extend the diprotodontian fossil record back by 30 million years," Mr Crichton said.
Co-author Associate Professor Robin Beck says the discovery raises the possibility these ancestors of modern Australian marsupials were also related to marsupials found in Antarctica and South America, where similar fossils have been uncovered.
As well as the Lumakoala, two other types of koala - Madakoala and Nimiokoala - have been reconstructed from the fossils found at the Pwerte Marnte Marnte site south of Alice Springs.
Professor Gavin Prideaux, director of the Flinders University Palaeontology Laboratory, said the additions to the fossil record meant there would have been at least seven koala species roaming Australia in the late Oligocene period (23–25 million years ago) - a "koala heyday".