What is an example of how isolation has affected the Australasian ecozone?

As a result of Australia's long isolation, the marsupials were the dominant mammalian group and evolved into a multitude of forms to fill roles typically occupied by placental mammals elsewhere in the world. Herbivorous marsupials, such as kangaroos and wallabies, occupied the niche of ruminants such as cattle and deer. Carnivorous marsupials, such as quolls and Tasmanian devils, occupied the niche of felids and canids. Even arboreal marsupials such as koalas and possums evolved.

However, the arrival of humans and placental mammals, such as dogs, foxes, and cats, had a devastating impact on the native fauna. Many species of Australian marsupials became extinct, and those that survived are now often confined to small, isolated areas.