Marsupialia

(vertebrate zoology) The single order of the mammalian infraclass Metatheria, characterized by the presence of a marsupium in the female.

An order of animals, long considered the only order of the mammalian infraclass Metatheria.

The marsupials are characterized by the presence of a pouch (marsupium) in the female, a skin pocket whose teat-bearing abdominal wall is supported by epipubic bones. The young are born in the embryonic state and crawl unaided to the marsupium, where they attach themselves to the teats and continue their development. In a few species the pouch is vestigial or has disappeared completely.

A wide variety of terrestrial adaptations are found among the 82 genera of living marsupials. Some spectacular examples of evolution convergent upon placental modes of life are exemplified by the Australian marsupial “moles” (Notoryctes), “wolves” (Thylacinus), and “flying squirrels” (Petaurus). For the most part, the adaptive radiation of the marsupials has paralleled that of the placentals, yielding many ecological analogs, such as kangaroos and wallabies, which are the counterparts of the placental deer and antelopes, although these groups differ widely in structure. See also Anteater; Eutheria; Kangaroo; Koala; Mammalia; Metatheria; Opossum.