“THE LAND DOWN UNDER”
THE ORIGIN OF AUSTRALIA AND ITS ANIMALS
40 million years ago
|The koala is a marsupial currently found along the southern and eastern coasts of Australia. Koalas fill the same ecological niche as the sloths, mammals of South America. Koalas have a very low metabolic rate, sleeping most of the time, and may be motionless for 16-18 hours at a time.
Credit: Photo Erik Veland, courtesy of Wikipedia.
By 80 million years ago, due to plate tectonics, the Australian landmass (originally containing New Guinea and Tasmania) began to separate from Antarctica (both landmasses containing marsupial mammals, then being much closer to the equator), and by 40 million years ago had no more contact with the rest of the Old World. It then began its unique evolutionary history dominated by marsupial mammals. Naturalist Alfred Wallace (along with Charles Darwin, the co-discoverer of evolution by natural selection) was one of the first to notice a biogeographical barrier separating the marsupial animals of Australia and adjacent islands from the placental mammals of the rest of the Old World. This became known as the “Wallace Line”.
Modern examples of marsupials in Australia include kangaroos, wallabies, koalas, and Tasmanian devils. A diversity of now-extinct marsupials existed in the past, including giant marsupial herbivores and marsupial meat-eaters (the “Tasmanian wolf” only went extinct in the nineteenth century). Humans were latecomers to Australia, and did not first arrive until perhaps 45,000 years ago (probably crossing water with the help of boats or rafts).
|The red kangaroo is one of the largest of the Australian marsupials. Male red kangaroos may leap over 9 meters (30 feet) in one leap.
Credit: Photo by Dellex, courtesy of Wikipedia.
HOW DO WE KNOW?
Fossils from well-dated deposits in Australia, New Guinea and Tasmania indicate that the marsupials supplanted placental mammals in this region and became the dominant form for the last 50 million years.
WHY SHOULD I CARE?
The Australian continent can be considered a great “test tube” for evolutionary change, showing evolution of similar animals filling similar niches in completely different, separated parts of the world. That is, from different starting points, starting on the one hand with a group of early placental mammals in much of the world and, on the other hand, starting with an early group of marsupials isolated in Australia, evolutionary pressures led to animal forms that filled similar niches in each evolutionary scenario, sometimes producing marsupials that look remarkably like placental mammal counterparts such as dogs, shrews, moles, and mice, or else fill much the same niche.
This website tells all about extinct Australian mammals and the fossil record.
This encyclopedia website explains all about the geological history of Australia.
This is a website with links to information and pictures of Australian fauna.
This is a kid-friendly site about Australian fauna.