Cave divers have long guarded the extensive subterranean systems surrounding Mount Gambier as one of the country's prime resources for the harrowing hobby.

Cave diving is the otherworldly outcome when two perilous pastimes in their own right - spelunking and scuba diving - are combined to create one of the more treacherous activities in existence. It's certainly not for the faint hearted or claustrophobic.

But for palaeontologist Julien Louys, donning a scuba suit and descending into the gloomy depths is more than worth it for the secrets they shroud.

The Griffith University researcher recently joined members of the Cave Divers Association of Australia (CDAA) as they plunged into the Gouldens, Engelbrecht and Tank caves to recover fossils of some of Australia's most mysterious animals: extinct marsupial megafauna.

The inaccessibility of the caves is a blessing and a curse to researchers.

Fewer people have entered the Tank cave's claustrophobic bone room than have set foot on the surface of the moon, leaving its fossils unmolested for millennia.

By studying the preserved fossils, Dr Louys hopes to reconstruct the environments the prehistoric creatures lived in and develop a better understanding about why they went extinct.

"Palaeontology is more than just studying dinosaur bones," he said.

"Where the fossils come from, their context, age and relationship to other fossils is critical information we use to understand past environments and how climate change impacted ecosystems in the past.

"That's one of the most long-ranging debates in Australian palaeontology and global palaeontology, what happened to these megafauna?"

The megafauna, which included wombats weighing over a ton and an echidna the size of a sheep, went extinct towards the end of the Pleistocene era about 12,000 years ago.

"One of the key debates is whether it was humans that caused their extinctions or whether it was environmental change that caused their extinctions," Dr Louys said.

"There's been a lot of conjecture or a lot of hypotheses that humans may have caused the extinctions because climate changes weren't severe enough or weren't impactful enough.

"But one of the gaps in our knowledge of that time, and of these species, is what sort of environments they actually lived in and what sort of ecologies these megafauna species had."

The highly soluble limestone rock for which the region gets its name has over time weathered to form the spectacular sinkholes that attract scores of tourists each year.

In 2022, Dr Louys played an instrumental role in winning protections for key cave sites on the Limestone Coast to ensure the fossil record is preserved into the future.

South Australia listed Green Waterhole, which contains the only known extensive underwater vertebrate fossil deposits in Australia, on the State Heritage Register, meaning visitors can only access the site with supervision, reducing the risk of disturbance.

Dr Louys and the CDAA would like to see further protections imposed on cave sites in the region.

"Some of these sites are at risk of being lost forever," he said.

"They provide not only a window into Australia's past but their fossils can help educate and inspire Australians about our environments and are instrumental in understanding how past climate and environmental change affected ecosystems, fauna, and flora.

"The laws and legislation concerning fossil protection in Australia are not very clear, not consistent across states and territories and rarely if ever enforced.

"If these are lost or destroyed, they're gone for good and whatever we might be able to learn about Australia and our future wasted."

Australian Associated Press