Natural History of Australia - Isolation

Isolation

Australia separated from Gondwana 99 Ma, and initially remained warm and humid with rainforest vegetation. Inland Australia had systems of rivers and lakes with abundant wildlife. Fossil birds, platypus, frogs and snakes are present from this period. From 30 Ma there was a period of global cooling and from 15 Ma the Antarctic ice sheet formed. Sand deserts and large inland salt lakes formed within the last 5 Ma. Climatic oscillation during the Pleistocene during the last million years led to repeated phases of glaciation with lower sea levels that linked Australia to New Guinea and warmer interglacial periods with higher sea levels.

As early as the Miocene (23 to 5.3 Ma) and into the Pleistocene (20,000-50,000 years before present) the Australian megafauna developed. The megafauna became extinct in the late Pleistocene, at a time coinciding with both a period of climate change and the first human habitation of Australia. Recent analysis suggests that the fire-stick farming methods of the Australian Aborigines reduced plant diversity and contributed to the extinction of large herbivores with a specialised diet, like the flightless birds from the genus Genyornis. The World Heritage listed Naracoorte Caves in South Australia are the best record of the Australian megafauna. The placental mammals made their reappearance in Australia in the Pleistocene, as Australia continued to move closer to Indonesia, both bats and rodents appearing reliably in the fossil record. The geographic isolation of Australia created a sharp division between Australian fauna and Asian fauna at the Wallace line.