Theories of the Extinction of the Australian Megafauna

Australia: The Land Where Time Began

Theories of the Extinction of the Australian Megafauna

The extinction of the Australian megafauna has been discussed and argued over for 150 years with no consensus being reached. according to Johnson (2006) the difference of opinion among the researchers in the field have become deeper. In his book, Australia's Mammal Extinctions, he considers a wide range of theories.

The first fossils of megafauna animals, in this case a Diprotodon, from the Wellington Caves of New South Wales were sent for scientific description to Sir Richard Owen in England. This discovery of megafauna fossils were important because they added support for Darwin's 'law of succession of types', each region has its own distinctive suite of fossil species related to the present-day animals in that region, but not ancestral to faunas from other regions. It supported the evidence that had been recently accumulating from the other continents that there had been an extinction of giant animals from around the world in the geologically recent past.

Owen included the fossil marsupials to confirm his belief on the causes of extinctions, that he believed occurred before the advent of humans because they failed to 'adjust' changed environmental conditions brought about by "continuous slowly operating geological changes' that affected the availability of resources necessary for life. Owen believed the large species would be more susceptible to these changes because they required more food and water. He also believed that humans had contributed to the extinction of many of large animals, from Europe in particular where 'a rude primitive human race' had been found with the remains of extinct mammals (Owen, 1861). Even before there was any evidence of the the extinctions in Australia taking place after the arrival of humans, Owen believed that humans had been the main cause of the megafauna extinction in Australia, because 'no other adequate cause presents itself to my mind save the hostile agency of man' (Owen, 1877). He noted the large size of the animals and believed they would have moved too slowly to escape.

In the late 19th century and the early 20th century the most common view was that extinctions were caused by the drying climate at the end of the Pleistocene. At least partly because of the presence of the megafauna, it was generally believed that the climate during the Pleistocene was cool and wet, implying that wherever the soil was productive enough the continent was covered with the luxuriant vegetation that was believed to be essential to support such large animals (Wilkinson, 1885). According to this belief, it was the conversion of the continent to mostly dry plains with sparse vegetation that caused the extinction of the megafauna. Wilkinson saw the fossils at Cuddie Springs as evidence of the final stages of this drying of Australia. Others agreed with Wilkinson as to the cause to the extinction, such as Browne (1945). Some such as Norman Tyndale-Biscoe (1959) disagreed on the basis that it didn't explain the survival of many mammal species in arid central Australia as well as the extinction of megafauna animals in New Guinea, that didn't dry out, suggesting that the Aboriginal People may have killed off some of the large species, the remainder going extinct after the arrival of the dingo.

The idea that the dingo was responsible for the disappearance of the megafauna was refuted by Gill (1955) on the basis of the megafauna going extinct in Tasmania where the dingo never reached. He also doubted other explanations, and added his own suggestion, that was actually the variability of the climate at the Pleistocene-Holocene boundary, and during the Holocene, that brought rapid changes that the larger animals couldn't adapt to quickly enough. He also believed that as different animals have different temperaments, some being more resilient and tenacious than others, those that went extinct would have been the ones he thought of as 'psychologically weak in some way that explained their sensitivity to a range of impacts' (Johnson, 1955).

Johnson discusses a number of other suggested causes of the extinction.