Nothing except seals, some bats and some birds made it to Australia in millions of years.
Humans conquered Australia a few times just within some ten thousand years.

I think even the people who work on this professionally, have a hard time scaling those timeframes. It seems that mammals evolve rather slowly compared to humans who made huge leaps within possibly just thousands of years.

Moving a population across oceans (deserts, jungles), creating a new line and then blending it again just some thousand years later seems to be an incredibly strong force for evolution.