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.

Most of the megafauna species became extinct late in the Pleistocene Epoch, perhaps 20,000 years ago. The Aborigines arrived in Australia at least 60,000 years ago, and so probably shared the continent with many megafauna species for millennia. Whether the Aborigines had a role in the final extinction of these creatures, however, remains unclear. Aboriginal hunting, or their use of fire, which led to an increase in grasslands and dry forests, may have been partly responsible but it is likely that the drought condition which occurred at the peak of the last glaciation about 18,000 years ago was also involved.

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.