The marsupial lion, Thylacoleo, is one of Australia?s most extraordinary megafauna (extinct giant animals). It is thought to have died out about 46,000 years ago, at the end of the Pleistocene Period. This Thylacoleo was discovered in a remote part of the Nullarbor Plain by a group of cavers: Ken Boland, Ray and Chris Gibbons, Peter Ackroyd, Nicholas White, Darrel Carr, Margaret James, Paul Devine and Eve Taylor. In May 2002, using an ultra-light aircraft, they discovered about 150 geological features of interest, including three caves with megafauna remains.

The Nullarbor contains numerous sinkholes and caves, some of which are rich in fossils. Over time, the sinkholes have become death traps for animals that fall in and then crawl away along lateral cave extensions to die. Numerous animal bones have been preserved in the stable, dry, dark conditions of the Nullarbor.

This site is now recognised as one of the most important megafauna sites in Australia.

The cavers? find was initially reported to staff of the South Australian Museum who, realising the site was in Western Australia, contacted Dr John Long, Curator of Vertebrate Fossils at the Western Australian Museum.