Old elements of Australia's fauna derive from the conjunction of Australia with other continents in the Mesozoic era. With South America, Africa, Antarctica, India and New Zealand Australia was part of the super continent Gondwana. First, India, then Africa and then New Zealand split away about 140 million years ago. The remaining continents separated from each other at the end of the Mesozoic era (70 million years ago). By about 40 million years ago ago, Australia was fully separated from Antarctica and commencing a northward drift as an isolated continent. Australia was isolated for a long period, during the whole Tertiary up to the Pleistocene. Thereby Australia�s fauna developed a high autonomy. Many endemic species, genera and even subclasses have been found on the continent. First, placentals and marsupials both were represented on the continent, but soon the placentals died out and marsupials spread out to occupy many niches where, in other continents, placentals were found. Marsupials came to occupy most nutritional niches, including herbivores, nectivores, insectivores, carnivores, saprophages and omnivores. As Australia moved closer to the Asian land masses, immigration occurred. A few mammals (rodents, bats, dingo) and also lizards, snakes, birds and insects colonised the heretofore isolated continent in this way.
Since mountains in Australia account for only a small percentage (0.15%) of the land area and Australian mountains are not as high or as isolated from the surrounding area as other mountain ranges in the world, the specific alpine mammal fauna is small and infiltration by lowland genera has occured to a greater extent than in alpine regions elsewhere. However, for some invertebrate species, including beetles and spiders, the mountain tops have acted as geological islands and contain endemic species with a biological lineage of 80-100 million years ago.
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