Marsupials

Marsupials have developed a unique reproductive system: They give birth to altricial, or minimally developed, young that climb from the vulva of their mother into a marsupium — an abdominal pouch or fold in their mother's skin — to nurse as they continue to grow. This and other differences have persuaded systematists to place marsupials in their own separate subgroup, infraclass Metatheria(See Mammal Orders), and to organize them into seven orders, as shown at left below. Since Australia drifted apart from Antarctica (See Mammal Migration), Australian marsupials have evolved in isolation, developing into many forms — today there are more than 200 species that fall in into four groups: the carnivorous marsupials, such as the Tasmanian devil; the bandicoot group; the marsupial mole; and the diprodonts, which include kangaroos and koalas. Many of them have assumed lifestyles similar to those lived by placentals elsewhere. For example, kangaroos — not gazelles or antelopes — graze on Australian grasslands; koalas — not monkeys — live in the trees; and there are marsupial squirrels, anteaters, moles and cats.

In the Americas, where competition with placentals has been stiff, all but one of the 70 surviving marsupials are opossums. Nocturnal and omnivorous, they are either arboreal or terrestrial creatures, all except for the yapok (Chironectes minimus), which lives in the water. The Virginia opossum is the only marsupial that lives north of Mexico.

Next >>Anteaters, Sloths and Armadillos

Mammals By Class: Monotremes Marsupials Anteaters, Sloths and Armadillos Insectivores Tree Shrews Colugos Bats Primates Carnivores Cetaceans Sirenians Elephants Ungulates Hyraxes Aardvarks Pangolins Rodents Lagomorphs Elephant-Shrews Main Menu