When Australia broke off from Antarctica maybe 50 or 60 million years ago, it was at a high southern latitude, where conditions were usually moist and cool. It had forest over the whole country, so it had a very damp, cool and forested land. Then it slowly drifted north towards Asia, and in that process, it moved from those temperate latitudes to the subtropical high-pressure zone, where the continent became both warmer and drier. Therefore, the inner of the continent in particular dried out. And the fossil record shows the vegetation and the fauna adapting to those much more dry conditions.Superimposed on the long-term shift from that a cool, moist climate into subtropical aridity, the world entered an ice age about two million years ago with glacial/interglacial cycles. Consequently, the last two million years of that 50 million-year journey was a period of high-amplitude climate change, from relatively warm, wet climates to much drier and colder climates, back and forth repeatedly. And these transitions occurred rapidly, many times over a few hundred to a few thousand years. This would have been a very different kind of climate stressor from the more gradual shift towards aridity.
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