Prior to the arrival of humans in Australia, the continent was marked by dense forests and massive animals the size of cars.

Australia's Super-Large Animals

About 45, 000 years ago, however, a large percentage of the Australian megafauna, large animal species with body mass about 130 percent greater than those of their closest relatives that live today, went extinct.

The cause of these gigantic animals' extinction has long been debated by scientists but findings of a new study, which was published in the journal Nature Communication on Jan.20 indicate that human activity could be blamed for the gradual extinction of Australia's megafauna, which includes 2-ton wombats, 1,000-pound kangaroos, 25-foot-long lizards,300-pound marsupial lions, 400-pound flightless birds and Volkswagen-sized tortoises.

More Than 85 Percent Of Megafauna Went Extinct After Humans Arrived In Australia

Study researcher Gifford Miller, from the University of Colorado Boulder, said that more than 85 percent of Australia's super large birds, mammals, and reptiles were decimated after the arrival of humans in Australia.

Scientists also consider climate fluctuations as a possible cause of the gigantic animals' demise but Miller said that there is no evidence that a significant change in climate occurred during the period when the megafauna went extinct. He said that the demise of the animals could be blamed on imperceptible overkill.

Extinction Not Necessarily Through Intensive Hunting

Although the study blames human activity as an important cause of megafauna extinction, researchers think that the animals' extinction is not necessarily through intensive hunting. They think that even low-intensity hunting could have significant effect on the animals' likelihood to survive.

A research published in the Quaternary Science Reviews journal showed that early human settlers in Australia lived alongside some of the megafauna for thousands of years prior to the extinction of the animals which means the megafauna did not go extinct soon after the first Australians arrived.

Vulnerable Even To Low-Intensity Hunting

An earlier study though suggested that even low-intensity hunting of the Australian megafauna, or killing one juvenile mammal per human per decade, could still have an eventual impact on the species' ability to survive.

"We show that remarkably low levels of exploitation of juveniles (the equivalent of one or two kills per 10 people per year) would have been sufficient to drive these large species to extinction within centuries, as a consequence of their "slow" life-histories," the 2006 study reads.

Low-intensity killing could have led to the extinction of the species in a few hundred years since large mammals are demographically vulnerable to the effects of hunting due to their low reproduction rates and low population.

By killing just one juvenile male every year, humans limited the animals' ability to reproduce which led to a gradual decline in their population and their eventual extinction.

"Our results provide the first stratigraphically constrained sequence of events for Australian megafaunal extinctions, rule out extreme aridity and habitat change as causal mechanisms, leaving human agency, specifically imperceptible overkill as the most probable extinction cause," Miller and colleagues wrote in their study.

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