A mini koala meandered through central Australia about 25 million years ago. The newly discovered species belonged to a community that contained the oldest known members of the koala family – and it could provide crucial missing information on the mysterious early evolution of marsupials.
The novel species – which has been named Lumakoala blackae – is represented by just by a dozen ancient teeth, mostly upper molars, found in fossil-bearing rocks near Alice Springs.
“Teeth are good because they provide a huge amount of evolutionary and dietary information,” says at Flinders University in Australia who led the analysis of the fossils. Since tooth shape doesn’t tend to vary a lot within species, differences between species can serve as “road maps for understanding the evolution of their relationships”, he says.
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The teeth suggest that L. blackae weighed between 2.2 and 2.6 kilograms – tiny compared with the modern koala (Phascolarctos cinereus), which weighs between 4.1 and 13.5 kilograms. It probably munched away at relatively soft plant material, like young leaves and small fruits and maybe the occasional insect, rather than the tough eucalyptus leaves that today’s koala eat.
What’s more, L. blackae shared its environment with other koalas. Fossil teeth found in the same rocks belong to two previously known genera of prehistoric koalas, Madakoala and Nimiokoala. Also present in the community were perhaps two or three species of Ilariidae – a family of massive, koala-like marsupials weighing upwards of 200 kilograms that were the biggest land mammals in Australia at the time. “That’s really cool,” says Crichton.
This suggests that, 25 million years ago, marsupials thrived in large, multi-species communities, says at The University of Queensland in Australia.
The discovery also helps throw new light on a 30-million-year gap in Australia’s fossil record. We know from fossils that some very primitive species of marsupials inhabited the landmass 55 million years ago, says Price. There is also evidence from fossils that most of the modern marsupial groups – such as kangaroos, possums, bandicoots and koalas – had appeared by 25 million years ago.
“What the heck happened in between?” says Price. “There are a lot of mysteries about where Australian marsupials came from.”
Although L. blackae comes at the end of that fossil gap and is “definitely something closely related to koalas”, says Price, it also shares characteristics with other non-koala marsupials of today. This means it could represent a species closer to the primitive state from which Australia’s previously mega-diverse marsupial communities thrived – an idea that could be explored further with more fossil specimens.
“Diversity across so many marsupial groups has dwindled dramatically,” says Price. “Today is the first time in the past 25 million years that there is only one koala species present.”
Scientific Reports
