Marsupials: Opportunity to evolve
None of the marsupials that lived in the central part of the southern super-continent which became Antarctica survived. By that time Antarctica had drifted over the South Pole where it was so cold that it developed an immense ice cap and life on the land became insupportable. The eastern section of the super-continent, which became Australia had drifted in a north- east direction into the emptiness of the Pacific basin and has since remained totally separate from any other continent. The marsupials that occurred on this section of the super-continent have continued to evolve without any invasion from placental animals until man introduced them. During this time, the marsupialsradiated into a great number of different forms in order to take advantage of the wide range of environments and opportunities available to them. Fossil remains of some spectacular species that once existed have been discovered in the limestone caves of Naracoorte, 250 kms south of Adelaide. Among them are the remains of a huge marsupial the size of a cow, with a head like a small giraffe that browsed on the branches of trees. One specimen Thylacoleo was originally thought to be a carnivore due to the back teeth that were elongated into formidable shearing blades, and called a marsupial lion. More recently the front legs have shown that this animal was well suited for a tree climbing existence and used its elongated back teeth to cut down hard fruits.