The splitting world
In order to explain how the marsupials got from South America where they originally radiated to Australia we have to return to the period when the dinosaurs were still at the height of their dominance. At that time, the continents of the world were grouped together in a single large land mass. Consequently fossils of closely related dinosaurs have been found in all of today's continents. The early mammal like reptiles would have similarly widespread distributions. About 135 million years ago the large single land mass (Pangaea) split into two a northern supercontinent called Laurasia comprising today's Europe, Asia and North America; and in the south, another super-continent called Gondwana made up of South America, Africa, Antarctica and Australia.