Evolution and function of mammal skulls
Where are the mammals?
This is the story of a small and isolated continent, with important nearby islands. Australia’s historic break-away from Antarctica (which holds marsupial fossils) and South America in the early Neogene provided isolation that allowed four orders of Marsupials to diversify in the relative absence of other mammalian groups. Australasia is, however, also home to the only modern Monotremes (platypus and echidnas), which were part of the isolated mammal fauna that inhabited this continent from the beginning of its northward movement on the Australian tectonic plates. Australia’s bats and rodents arrived on that continent from the north, beginning around 15 million years ago, as Australia approached the Asian land mass and its associated southern archipelagoes. Australia’s vast deserts hold unique mammals, both marsupials and rodents. The eastern edge of the continent holds the only mountain chain, providing diversification of habitats for mammals found only in those areas. New Zealand, a pair of large islands, represents extreme isolation; until the time of human colonization the only mammals were bats and marine mammals–no native land mammals at all.