Hear "Marsupial" and one thinks Kangaroo! While the Kangaroo is the most popularized one by cartoons and storybooks, there are many other marsupials as well. The Koala, Opossum, and Tasmanian wolf, to name a few.
Marsupials are a group of animals that belong to the highest developed class of animals called the Mammals. The most common feature shared by all Marsupials is the presence of a pouch or a marsupial. Moving an evolutionary step away from the egg-laying mammals, the marsupials give birth to their young. However, the young are very immature, and soon after birth crawl into the pouch, where they live and are nursed, until they are fully developed to be on there own.
Most marsupials are confined to the regions of Australia, New Guinea, and South America. The Virginia Opossum is the only one that is in North America. Theories for this isolation have always been in quest.
One of the main theories is the Continental drift. Simply put, millions of years ago, Australia and South America were bridged by the Antarctica. As the Continents drifted apart, a body of water separated them. This lead to the marsupials being on separate terrain and evolved independent of each other, yet maintaining the primary characteristics, a feature called Parallel Evolution. The discovery of fossil bones in this land bridge further validates this theory. All this is postulated to have happened during the Cretaceous era. The drifting of the continents, leading to the divergence of animal population happened simultaneously.
More recently there has been another theory of continental drift. It suggests that the marsupials could not have entered Australia via Antarctica. It suggests that they had evolved in a land mass originally situated in the Central Pacific. The land mass split in the early Jurassic era. One portion drifted towards New Guinea and Australia. The other side drifted toward North America and the marsupials finally colonized in South America.
There is also some scientific evidence that suggest that the climatic conditions and the fauna and vegetation of those areas was much warmer in those areas during the pre historic days, which was good for the marsupials.
The marsupial population in other parts of the world was dwindling. One reason was the emergence of the placental mammals, like fox and dogs, higher up in the hierarchy of the animal kingdom. Compared to them, the survival rate of the marsupials was low. The placental mammals competed with the marsupials for food, and even preyed on them.The human element was also not favorable to them, since farmers killed the crop destroying marsupials. The saving grace for them in Australia was the fact that due to its isolation from the other regions of the world, there were no native placental mammals, which minimized the competition.
Today, efforts are being made to keep them from being an endangered species. In the mean time, kids, and adults too, look to Australia and South America, when they think of these estranged animals.