A marsupial is a very special kind of mammal. Although it does give birth to live young, they are very immature when born. Their mothers have a pouch on their abdomens, where the babies are protected and can drink milk until they are ready to survive in the open.
Marsupials are the group of mammals commonly thought of as pouched mammals. They give live birth, but they do not have long gestation times like placental mammals. Instead, they give birth very early and the young animal, essentially a helpless embryo, climbs from the mother’s birth canal to the nipples. There it grabs on with its mouth and continues to develop, often for weeks or months depending on the species. The short gestation time is due to having a yolk-type placenta in the mother marsupial. Placental mammals nourish the developing embryo using the mother’s blood supply, allowing longer gestation times. Like other mammals, the marsupials are covered with hair. Mothers nurse their young — a young kangaroo may nurse even when it has grown almost to the mother’s size.
In South America and Australia, however, marsupials continued to be an important group of land mammals. Many South American forms are similar to the North American opossum. The marsupials of South America began to go extinct in the late Miocene and Early Pliocene when a land connection with North America formed, allowing placental mammals to cross into South America. In Australia, though, marsupials continue to be very diverse, and are the dominant native mammals. They include kangaroos, koalas, tasmanian devils, wombats (above right), and other typical Australian mammals. Until recently, they also included the marsupial wolf, Thylacinus (below). Like the quagga, the marsupial wolf is now extinct. The last individual was seen in Tasmania in the 1950s.
There are several cases of convergent evolution between marsupials and placental mammals, in which the two animals have evolved to fill the same ecological niche in different parts of the world. There are burrowing forms, grazing forms, gliding forms, and even long-snouted ant-eating forms which have evolved independently in the two groups.
Picture Credit : Google
