Researchers are heading into the deep in regional South Australia to uncover the secrets of the larger-than-life creatures that once roamed the landscape.

SA’s Limestone Coast was once home to massive animals such as the short-faced kangaroo, which stood two metres tall and weighed up to 200 kilograms.

The remains of the short-faced kangaroo and other megafauna lay fossilised in a system of limestone caves the region is famous for.

A Griffith University team is focusing on the caves, including Goulden’s Sinkhole near Mount Schank and Tank Cave at Tantanoola.

“We’ve got all sorts of megafauna down there — we’ve got short-faced kangaroos, we’ve got thylacoleo, which is the marsupial lion and probably the largest marsupial predator that ever lived,” associate professor Julien Louys said.

“We have all the bones of these animals spread out on the floor of these caves in an underwater setting.

The project involves the extraction of fossils from the caves and the installation of gamma radiation readers.

Fossils release certain amounts of gamma radiation as they age, which can allow researchers to estimate how old they are.

Teeth are one type of fossil Dr Louys wants to date.

“Enamel is about 98 per cent hard mineral and it essentially accumulates a gamma dose through time,” he said. 

“By measuring how much gamma dose the tooth enamel has, we can actually calculate how long it’s been buried.”

Caves once part of seabed  

The caves are located inland and dotted around the region, with their entrances often found on farmland or as large sinkholes. 

During times of low sea levels, such as the ice ages over the past 100,000 years, water levels in the caves were low or they were completely dry. 

As the ice melted and sea levels rose again, the caves filled with water and created the state they’re in today. 

One question raised by the presence of the fossils is whether the animals died in the caves while they were dry, or while they were filled with water. 

Navigating the underwater caves is no easy task, with only highly experienced and accredited divers able to head underwater. 

At Tank Cave, where remains of the short-nosed kangaroo are submerged, the 1.8-kilometre return dive takes about 4.5 hours to complete. 

The Cave Divers Association of Australia is volunteering its divers to help with the research project.

Site director Kelvyn Ball said divers had great respect for the caves and the history they keep. 

“It’s fascinating just to see how old the cave is and how long it’s been here before we entered it,” he said. 

“All this research will tell us how long ago all this stuff happened. 

The ‘big question’ 

By closely studying these fossils, Dr Louys and his colleagues hope to find out more about how megafauna lived.

“A bone by itself doesn’t tell you a huge amount, what we want to know is the environment they’re living in, the age that they’re living in and all sorts of other creatures and plants that would’ve been around at the time,” Dr Louys said. 

“One of the analyses we’re looking to do is trying to get pollen that’s preserved in the sediment so we can see what plants were around. 

“We’re looking to get environmental and ancient DNA from the sediment so we can get all sorts of levels of organisms, from microbes to insects through to other plants and animals that haven’t been preserved as fossil remains.”

Dr Louys said finding out how megafauna became extinct was the “big question” in Australia. 

“There’s two leading hypotheses about why they became extinct,” he said.

“It’s either humans arrived on the continent, engineered a whole heap of ecosystem change, hunted them and they became extinct, or it’s environmental change through time … impacted the megafauna.

“The likelihood is it’s probably a combination of both to various degrees, but … we just don’t have enough data yet from the bones and the fossils to know.”