(infraclass Metatheria, order Marsupialia)
A superfamily (or full order, Didelphimorphia) that comprises the opossums (family Didelphidae) and extinct relatives known since the Late Cretaceous. Possibly they are the least modified of all therian mammals. They are arboreal (except Chironectes, an otter-like, semi-aquatic form), mainly nocturnal, insectivorous or omnivorous marsupials, in which the marsupium may be well developed or (more usually) absent. There are more than three pairs of incisors in both upper and lower jaws. The second and third digits of the hind feet are didactylous. Didelphoids are distributed throughout tropical and subtropical America. There are twelve genera, and about 66 species.
Subjects: Zoology and Animal Sciences.