Study finds famous Australian caves are up to 500,000 years older than we thought - and it could help explain a megafaunamystery
South Australia’s is one of the world’s best fossil sites, containing a record spanning more than half a million years. Among the remains preserved in layers of sand are the bones of many iconic Australian megafauna species that became extinct between 48,000 and 37,000 years ago.
The reasons for the demise of these megafauna species are intensely debated. But the older the fossils we can find, the better we can understand the species’ evolution and extinction.
To date, determining the precise age of the caves has been difficult. However our research demonstrates, for the first time, how old Naracoorte’s caves really are – and the answer is up to 500,000 years older than previously thought.
Our findings shed new light on the antiquity of this important place. We hope this will aid understanding of how biodiversity responds to a changing climate over time.
Author provided
A moment in geologic time
Caves can be extraordinary time capsules, often preserving the remains of long extinct plants and animals in exquisite detail. The Naracoorte Caves in South Australia is one such example.
The cave complex is South Australia’s only World Heritage site. Among the remarkably diverse and complete fossil record are the remains of iconic megafauna such as:
- Thylacoleo carnifex (marsupial predator)
- Zygomaturus tribolus (huge herbivore)
- Wonambi naracoortensis (giant constrictor snake)
- Procoptodon goliah (browsing sthenurine kangaroo).
Palaeontologists have excavated and dated many of these fossil deposits and reconstructed the skeletons of a number of megafauna species.
The caves formed when groundwater percolated through cracks in limestone rocks, dissolving them and forming cavities. They were previously dated at between 0.8 and 1.1 million years old – an estimate generated by dating a fossil dune ridge that lies over the cave complex.
But the methods used to date the dune ridge were not entirely suitable for the task. As such, a precise age of the caves had not been obtained, until now.
This intricate work involved in our study has taken five years, but it was worth the wait.
Jon Woodhead, Author provided
What we did
The dating method we used involved examining the beautiful calcite formations inside the caves. Collectively, these are called “speleothems” and they include stalagmites, stalactites and flowstones.
When speleothems form, tiny amounts of uranium – a radioactive element – are locked inside them. Over time, uranium slowly decays into the ele