Consider how the continent of Australia separated from Pangea before the rise of Mammalia, and marsupials became the dominant animals of Australia, while they were displaced by mammals everywhere else.
Marsupials are also mammals. They appeared before the emergence of placental mammals, which is why there are no placental mammals native to Australia.
Also, you know that Opossums are marsupials, right?
Every possum I see gets the 17hmr treatment. Gross ugly animals that steal cat food.
