Palaeontologists say the discovery of a fossil off Eyre Peninsula's west coast could present possible evidence of human and megafauna interaction between 40,000 and 120,000 years ago.
Honours student Fraser Brown and palaeontology lecturer Aaron Camens collected fossils of 29 mammal species during an expedition to Brothers Island – one of only two sites on the Eyre Peninsula where extinct animals can be found.
Mr Brown, who studied the samples as part of his honours thesis into the decline of mammals on the Eyre Peninsula, said exploring the island wasn't straightforward.
"The Brothers is a very unique cave site in that it's definitely not a cave anymore," he said.
"What you actually see is a cove in the edge of the island and that might represent the interior of the cave that's been cut through almost and the fossil material is sitting in the rock in there."
Brothers Island, located between Coffin Bay and the finger of land known as Little Douglas, was mined in the late 1800s for guano, which is rich in a compound called phosphate.
"The fossil material is actually layered within the rock which means that it's exposed to the phosphate and it's then very very hard to then get out of the rock because it all lithifies together and it's very hard to break apart," Mr Brown said.
"So we actually rely on the waves a little bit to get the bones out before we can actually identify anything."
Mr Brown said evidence of some big mammals was found among fossils.
He said the largest included a kangaroo that was about 130 kilograms.
"We also have some really, really strange short-faced sthenurine kangaroos that were mobbing about in the area … we also found some smaller animals like the native cat and the quolls," he said.
"One of the most air punching moments for me was when we were actually filtering through the material and we pulled out the jaw of a thylacine … which is a very enigmatic animal in Australia."
Possible human interaction
Mr Brown said while it was hard to determine the age of the fossil, the deposit it was in could be up to 120,000 years old.
He said there were a number of reasons why the animals may have ended up in the cave site, including to seek shelter or by falling inside.
"Sometimes a predator will bring an animal into a cave as well and that's one of the things that we actually saw in the fossil material," he said.
While no human remains or indication of human activity were found at the cave site, Mr Brown said one fossil did present possible evidence of human and megafauna interaction.
"There seems to be a toe bone from one of the short faced kangaroos that might have some marks on it that could be butchery … but that's an interesting wrinkle in this story," he said.
Understanding the past
Mr Brown said while the deposits revealed there was a healthy ecosystem in the Pleistocene about 100,000 years ago, the arrival of agriculture and deforestation with European settlement resulted in serious native impacts on the Eyre Peninsula.
"The Eyre Peninsula is one of the worst places for mammals in Australia – in some places it gets down to just three or four species," he said.
Dr Camens said Mr Brown's project was important as it increased researchers' knowledge of the distribution of megafauna at a regional and continental scale.
"Places like the Eyre Peninsula that don't have very many deposits at all — these are crucial in figuring out how the environment has changed through time in these areas and what animals used to be around when the climate was different to how it is today," Dr Camens said.
He said the sediment samples were being processed to determine the age of the fossils.
"There is potential for the site to be pre-human completely or to be younger than when humans first arrived in Australia and that's one of the exciting things that we're looking forward to finding out," he said.
