Australian megafauna some 50,000 years ago included half-ton kangaroos, 2-ton wombats, 7-metre-long lizards, 180-kilo flightless birds, 140-kilo marsupial lions and tortoises the size of compact cars.
     Shortly after the arrival of the first humans around 45,000 years ago, more than 85 percent of Australia's mammals, birds and reptiles weighing over 45 kilos went extinct, and new evidence suggests that humans, not climate change, were the cause.
     Scientists have been debating the causes of the Australian megafauna extinctions for decades.
     A team of researchers used information from a sediment core drilled in the Indian Ocean off the coast of southwest Australia to help reconstruct past climate and ecosystems on the continent. The core contains dust, pollen, ash, and spores from a fungus that thrived on the dung of plant-eating mammals, allowing scientists to look back through more than 150,000 years - the last full glacial cycle. They found tungal spores from plant-eating mammal dung were abundant in sediment layers until about 45,000 years ago, after which they declined rapidly over just a few thousand years.
     Southwest Australia is one of the few regions on that continent having dense forests both 45,000 years ago and now. The area also contains some of the earliest evidence of humans on the continent.
     Study participant and Colorado University professor Gifford Miller says there is no evidence of significant climate change during the time of the megafauna extinction, and the real cause may have been "imperceptible overkill." A 2006 study indicates that even low-intensity hunting like the killing of one juvenile mammal per person per decade could have resulted in the extinction of a species in just a few hundred years.

Edited from Popular Archaeology (20 January 2017)