First ever complete skeleton of a marsupial lion, Thylacoleo carnifex, from the Nullarbor caves.
Image: Clay Bryce, WA Museum
Source: Clay Bryce, WA Museum
Nullarbor cave fossils offer solution to the mystery of Australia's megafaunal extinctions.
Two main theories account for Australia’s megafauna extinctions, dated at around 40-45,000 years ago. One is that climate change, brought about by glacial ice ages which increase aridity, placed extreme pressure on the environment and they could not cope. The other is that they were decimated after the arrival of humans (c. 48,000 years ago), principally from landscape changes due to fire-stick farming.
However in a paper published today, Australian scientists conclude that extinction's smoking gun was held by fire-wielding humans.
In July 2002 an expedition from the Western Australian Museum led by Dr John Long (now Museum Victoria’s head of sciences) uncovered a veritable treasure trove of fossil skeletons belonging to Australia’s extinct megafauna.
The prize specimen was the world’s first complete skeleton of the marsupial lion, Thylacoleo carnifex, and the sites were recently named the Thylacoleo Caves.
World news at the time, the story featured on the front page of several Australian newspapers, and in August 2006 was the subject of a 30-minute documentary on the ABC’s Catalyst program.
The many skeletons found indicated that an unusually high diversity of animals once inhabited the now-desolate Nullarbor Plain. Unlike other sites these fossils were preserved in complete articulation, with animals assumed to have accidentally fallen down holes leading to underground caverns, from which they could not escape.
Dr Gavin Prideaux from the WA Museum has been working on the Nullarbor fossils and together with his team of experts has written a paper - the first outlining scientific results from the various studies - which was published today in the prestigious journal Nature.
The most remarkable discovery about these fossils (dated between 200,000-780,000 years old) is that isotopic studies on mammals’ tooth enamel, compared with living mammals from known habitats, demonstrate fauna was already adapted to an arid climate.
The range of plant-eaters found also suggests vegetation was more diverse than on today’s treeless plain. Among the fauna were 23 kangaroo species, including the largest of all time (Procoptodon goliah), and eight new species of extinct kangaroo, including two new species of tree kangaroo (genus Bohra).
This new data shows that if megafauna had already adapted to extreme aridity at least 200,000 years ago, climate change must not have been a major factor in their extinction, thus pointing to the arrival of humans as the principal cause of extinction.
References:
Prideaux, G.J., Long, J.A., Ayeliffe, L.K., Hellstrom, J.C., Pillans, B., Boles, W.E., Hutchinson, M.N., Roberts, R.G., Cupper, M.L., Arnold, L.J., Devine, P.D. & Warburton, N.M. 2007. 'An arid adapted middle Pleistocene vertebrate fauna from south-central Australia.' Nature 445: 422-425