Animals

Marsupials are a type or group of mammals that usually have pouches much like the kangaroo. These mammals give live birth instead of laying eggs - but the gestation period is not as long as placental mammals. They actually give birth quite early in the growing stage.

When the animal has been given birth to it is only an embryo helpless to do anything. It will climb from the birth canal to the nipples of its mother where it will grab on with its mouth and develop. It may take weeks or months to develop.

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.

The only naturally occurring marsupial in the United States is the opossum. In the past, however, marsupials were quite common. During the Mesozoic marsupials were very common in North America; more common, in fact, than placental mammals. They persisted here until the mid- to late-Tertiary.

Though marsupials today do not have as many species as do the placental mammals, they are quite structurally diverse. They range from small four-footed forms like the marsupial mole, to the large two-legged kangaroos.