Evidence of the former existence of the Australian megafauna was known by the Aborigines, and was soon discovered by the earliest European settlers. A large collection of fossils from Wellington Caves, west of Sydney, was sent to England by Major Thomas Mitchell in 1831 for examination by the renowned Sir Richard Owen. Other specimens were sent by Leichardt, Strzelecki and Goyder, and Owen was progressively able to identify a number of large, extinct marsupials and birds. The newly established Australian museums became involved in subsequent decades, and their work has continued to the present, with major excavations of fossils from sites in most states.

Evidence has emerged that it was harsh climate, and not human habitation of the continent, that was the slayer of the car-sized wombats, 2.5-metre tall kangaroos, sheep-sized echidnas and other extra-large beasts that once roamed the outback, according to Queensland University of Technology research. Gilbert Price and Gregory Webb, in the Australian Journal of Earth Sciences, said that Queensland megafauna of the Pleistocene era was already drought-stressed before going the way of the dodo. The new study backs the findings of a Melbourne-La Trobe university team which announced in August that megafauna at Lake Menindee, in western NSW, was already extinct before humans arrived in that region. Both studies contradict the view of Australia's high-profile scientist and intellectual, Tim Flannery, that early Aborigines wiped out Australia's megafauna.

The Queensland researchers unearthed and studied megafauna remains from the Queensland region of Darling Downs, which borders New South Wales, at the Kings Creek catchment. "No evidence of human interaction with pleistocene remains was observed in the site or in other nearby sites," says their article. "The apparent progressive megafaunal extinction on the Darling Downs does not support a sudden 'blitzkrieg' model resulting from human hunting. The gradual demise … is most parsimoniously attributed to increasing aridity in southeastern Queensland."

Dr Price said the drought profile of the fossil kangaroo populations was "identical to that of a modern drought-stressed kangaroo mob". He said that if human habitation wiped out the megafauna, the fossil record should show the animals being wiped out at the same point in time. But the Darling Downs site showed "a progressive, three-stage extinction over time that relates to periods of climate change".

Dr Webb said it is hard to pin down the exact dates that the megafauna died out, but it was between 80,000 and 30,000 years ago, during which time Australia was becoming progressively drier. Humans are believed to have come to Australia between 48,000 and 60,000 years ago.

He said the dry weather, or aridity, was associated with the last ice age and the spread of glaciers throughout the world. Because the weather was so cold, there was little evaporation, little humidity and, therefore, little rainfall, he said.

Much more research is needed to get a clear picture of the diversity of megafauna species which lived in Australia during the Pleistocene Epoch. However, a representative list of the species found so far would include the following:

• Diprotodon optatum was the size of a rhinoceros, and is thought to have been the largest marsupial ever to exist.
  
  
• Zygomaturus tasmanicus was a bullock-sized relative of Diprotodon. It and related species lived in the more forested areas of southern Australia.
  
  
• Palorchestes azael was the size of a bull, with long claws and a longish trunk. Imaginative writers have suggested it as the inspiration for the Aboriginal bunyip.
  
  
• Procoptodon goliah was the largest kangaroo ever. It belonged to the sthenurine family, which had shortened flat faces and forward-looking eyes.
  
  
• Thylacoleo carnifex, the so-called 'Marsupial Lion', was a leopard-like animal, and was almost certainly carnivorous and a tree-dweller.
  
  
• Zaglossus hacketti, a sheep-sized echidna whose remains were discovered in Mammoth Cave in Western Australia, was probably the largest monotreme ever.
  
  
• Mihirung Birds were giant flightless birds. They included Genyornis newtoni and Dromornis stirtoni, which was the heaviest bird known.
  
  
• Megalania prisca was an enormous goanna-like carnivore, at least 5.5 metres long, and with a weight of about 600 kilograms.