New research published in Science journal has shed light on the mysterious extinction of Australia’s remarkable collection of megafauna.
Australia was once home to an extraordinary collection of very large animals: rhino-sized wombat-like marsupials called diprotodons, giant kangaroos, a goanna bigger than the living Komodo dragon, a giant goose twice the size of the emu and many others.
All of these species became extinct about 40,000 years ago and until now it has been unclear why. Now it appears that human arrival rather than climate caused megafaunal extinction.
The extinction then triggered significant ecosystem changes such as the replacement of mixed rainforest by sclerophyll vegetation through a combination of direct effects on vegetation of relaxed herbivore pressure and increased fire in the landscape.
Professor Chris Johnson, from the UTAS School of Zoology, led the research team, working in collaboration with scientists from UTAS, the Australian National University, University of Adelaide, University of New South Wales and Monash University.
The research has solved the mystery by using a new method of tracking the abundance of large herbivores through time by counting spores of dung fungi. Professor Johnson said big herbivores produce lots of dung and there are specialised fungi that live in it.
“The spores of these fungi can be preserved in sediments in swamps and lakes. As those sediments accumulate over time, they create a historical record of the abundance of very large herbivores in the environment. Pollen and charcoal particles are trapped in the same sediments, so that it is possible to match up the history of abundance of large herbivores with changes in vegetation and fire. Then, radiocarbon can be used to date these things.”
Prof Johnson said the research centred on a swamp called Lynch’s Crater in Northeast Queensland, where the sediment record reaches back to 130,000 years ago.
“It showed that the abundance of large mammals was stable until just before 40,000 years ago, when it suddenly crashed.
“This rules out climate change as a cause of extinction, as there were several periods of climate drying before the extinction and they had no effect on abundance and when the animals did go extinct, the climate was stable. Although, the extinctions followed very soon after the time that people arrived in the region- so it seems that people did it” he said.