What explains the so diverse nature of Australia?

Australia has been isolated from the rest of the world for millions of years. Therefore, evolution on this continent proceeded much more slowly. Primitive species of plants and animals, which became extinct around the world, unable to withstand competition from more advanced species, have remained in Australia almost unchanged. These are oviparous mammals, numerous marsupials (wombat, koala, kangaroo), large flightless emu birds. When predators entered Australia with humans, many of these species became extinct.