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Biogeographic history: the great escape

Australia was once part of the Gondwanan rainforest super-continent.

Joined to Antarctica and linked to South America, the climate was warm and wet. The land was dominated by forest. No ice-sheets had formed. Even in Antarctica, giant conifers stood tall over broad-leaved flowering plants and moist air swirled as mists through the canopy. Sometime in the Early Eocene (between 50-40 million years ago), the breakup of the super-continent Gondwana began. The separation of Australia from Antarctica was now underway.

As Australia drifted north toward the tropics, it escaped the onset of the ice-house deep freeze that engulfed Antarctica. However, because of the formation of the southern ocean circum-polar current and the climate change that followed, the continent now began to dry out. Just as the climate was becoming too dry and hostile for rainforest, the uplift and formation of the eastern ranges began. Then, during the Miocene around 20 million years ago, volcanic activity started to reshape and reform the land. 

The formation of mountains close to the coast created higher altitude moist habitat for rainforest, increased coastal rainfall, and happened just in time to allow many of the Gondwanan rainforest lineages to survive. For some of the Antarctic flora, the conditions in Australia were no longer suitable, so as Australia (Sahul) collided with SE Asia (Sunda) and the New Guinea highlands were formed, they escaped into Asia.

To this day, Australia retains the highest diversity of the original Antarctic-Patagonian rainforest on Earth.