World Heritage-listed Naracoorte Caves 500,000 years older than previously thought, research reveals

New research into the world heritage Naracoorte Caves has revealed the site to be 500,000 years older than previously thought.

The Naracoorte caves are one of the largest and oldest fossils sites in the world, housing the bones of Australian megafauna species that became extinct between 48,000 and 37,000 years ago.

The caves were previously dated between 800,000 and 1.1 million years old, but new research has placed them to be at least 1.34 million years old.

The caves formed when groundwater penetrated cracks in limestone rocks, dissolving them and forming cavities.

The Naracoorte Caves are South Australia’s only World Heritage site housing fossils of megafauna such as the Zygomaturus trilobus (huge herbivore), Wonambi naracoortensis (giant constrictor snake) and Procoptodon goliah (browsing sthenurine kangaroo).

University of Adelaide’s vertebrate palaeontologist Liz Reed, who co-authored the newly published study, said the previous attempt at determining the age of the cave was undertaken by dating a fossil dune ridge that lay over the cave complex.

“The coastline used to be a lot closer back then, and above the cave is an old stranded dune line, but that’s sort of a bit of a rubbery estimate.” Dr Reed said

“We’ve managed to get a precise age from dating decorations inside the cave, and we’ve got an age of 1.34 million, but that’s actually a minimum. It’s probably older than that.”

The new study was conducted over five years and involved examining the stalagmites, stalactites and flowstones known as “speleothems”.

Dr Reed said researchers from the University of Melbourne spent time “crawling around in caves” collecting broken pieces of speleothems.

When speleothems form, trace amounts of uranium become trapped inside and over time, it decays into the element lead. This happens at a known, constant rate, meaning researchers are able to date them accurately. 

Dr Reed said the second part of the study involved determining when the caves first opened to the surface.

“There’s lots of pollen in the atmosphere and charcoal from fires, so when we see that embedded in the speleothem, we know that the cave was open to the air,” she said.

“Once it’s open to the air, animals can fall in, sediments can come in, and we get fossil deposits. So that’s telling us when the caves actually opened up and deposits formed, and that was around 600,000 years ago.

“We have this 600,000-year megafauna time capsule at Naracoorte, which is actually older than we expected. We’ve found fossils deposits up to around 450,000 years that was dated, so we’ve got another 150,000 years of records that we can find.”

Important Research 

Dr Reed said this research was important to determine why megafauna became extinct.

“We know those animals became extinct,” she said.

“The longer time record we have, the more lead up we have to event, and we can look at long-term patterns of environmental changes and really hone in on what caused those extinctions.” 

The findings will also help palaeontologists target new excavation sites to find older fossils within the Naracoorte Caves as well as determine fossil deposit ages at other cave complexes in Australia and around the world.

Research undertaken into sites such as the Naracoorte Caves can also help researchers understand how climate change influenced the environment in the past to determine what might happen in future.