Why megafauna southwest of Mackay went extinct

Dating back 40,000 years, they include a giant wombat, croc and a marsupial lion related to the koala

Palaeontologist Dr Scott Hocknull with an adult 'Pallimnarchus' (Giant Freshwater Crocodile) tooth discovered at the South Walker Creek site. Picture: Project Dig, Queensland Museum / BHP

PALAEONTOLOGISTS have explained why megafauna including giant wombats and marsupial lions found at a dig site southwest of Mackay went extinct.

Queensland Museum palaeontologist Dr Scott Hocknull and a team of scientists have spent more than a decade uncovering 16 megafauna species dating back 40,000 years at South Walker Creek, 40km west of Nebo.

An interpretation of what life would have looked like in tropical Australia 40,000 years ago before many of the megafauna went extinct. Picture: Andrey Atuchin, Rochelle Lawrence & Scott Hocknull © 2020 Queensland Museum

The unearthed species now extinct included the half-tonne Diprotodon related to wombats, giant reptiles like a 7m long freshwater crocodile and the Thylacoleo or Marsupial Lion – a relative of koalas and possums, Dr Hocknull said.

The 'Diprotodon optatum' (Giant Marsupial) is one of 13 extinct megafauna species discovered at the South Walker Creek site. Picture: Andrey Atuchin, Rochelle Lawrence & Scott Hocknull © 2020 Queensland Museum

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The Pallimnarchus (Giant Freshwater Crocodile) is one of 13 extinct megafauna species discovered at the South Walker Creek site. Picture: Andrey Atuchin, Rochelle Lawrence & Scott Hocknull © 2020 Queensland Museum

“(The Thylacoleo) is the size of a lion with meat-cleaving teeth and bone-crunching molars,” he said.

“It could essentially give you a bear hug and was potentially tree-dwelling as well – the first Australian instance of the drop bear.

“At 170kg in weight, it’s a huge animal and a nasty piece of work.”

The Thylacoleo (Marsupial Lion) is one of 13 extinct megafauna species discovered at the South Walker Creek site. Picture: Andrey Atuchin, Rochelle Lawrence & Scott Hocknull © 2020 Queensland Museum

Dr Hocknull said the “weird” species evolving over millions of years of isolation were discovered by chance during the Barada Barna people’s cultural heritage clearance at a BHP-operated site in 2008.

“It was a mind blow,” he said.

“I had just assumed, based on what we knew about the tropics, that there would be a handful of bones … (but) we saw literally hundreds of bones in the ground sticking out, some really well preserved.”

The 'Protemnodon' (Giant Forest Wallaby) is one of 13 extinct megafauna species discovered at the South Walker Creek site. Picture: Andrey Atuchin, Rochelle Lawrence & Scott Hocknull © 2020 Queensland Museum

Teaming with other scientists, they were able to date the fossils and work out what type of environment the megafauna lived in.

Dr Hocknull said the site, now a dried-up creek, was once teeming with lush grasses and rivers.

The Quinkana (Ziphodont crocodile) is one of 13 extinct megafauna species discovered at the South Walker Creek site. Picture: Andrey Atuchin, Rochelle Lawrence & Scott Hocknull © 2020 Queensland Museum

And a reason so many fossils were found, usually “scarce as hen’s teeth” in the tropics, was because the “massive” crocodiles dragged their prey into the river and billabongs, he said.

But they had not found human remains, Dr Hocknull said, suggesting over-hunting could not explain the megafaunas’ extinction.

The Palorchestes (Marsupial 'Tapir') is one of 13 extinct megafauna species discovered at the South Walker Creek site. Picture: Andrey Atuchin, Rochelle Lawrence & Scott Hocknull © 2020 Queensland Museum

“If we had people arriving 65,000 years ago and our megafauna on the eastern coast of Australia are still quite happy 40,000 years ago … then clearly, they didn’t just disappear rapidly.

“Instead, we (found) their extinction (was) coincident with major climatic and environmental deterioration both locally and regionally, including increased fire, reduction in grasslands and loss of freshwater.

“Together, these sustained changes were simply too much for the largest of Australia’s animals to cope with.”

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The Phascolonous (Giant Wombat) is one of 13 extinct megafauna species discovered at the South Walker Creek site. Picture: Andrey Atuchin, Rochelle Lawrence & Scott Hocknull © 2020 Queensland Museum

Project Dig is an ongoing partnership between BHP Mitsui Coal and the Queensland Museum.

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