Didelphimorphia is an order of marsupial mammals. Members of this order are called didelphimorphs, or opossums. They are primarily found in South America, though some are found in Central America and Mexico and one, the Virginia opossum, ranges into the United States and Canada. They have a variety of sizes, shapes, and fur patterns, and range in size from the 6 cm (2 in) (plus 9 cm (4 in) tail) Kalinowski's mouse opossum to the 55 cm (22 in) (plus 54 cm (21 in) tail) Virginia opossum. Didelphimorphs are primarily found in forests, as well as savannas, shrublands, and grasslands. Almost no population estimates have been made for didelphimorph species, though the one-striped opossum is classified as Critically Endangered with a population of less than ten, Handley's slender opossum is also critically endangered, and the red-bellied gracile opossum is extinct, having last been seen in 1962.
The 93 extant species of Didelphimorphia are grouped into a single family, Didelphidae, which is divided into four subfamilies: Caluromyinae, containing four species in two genera; Glironiinae, containing a single species; Hyladelphinae, also with a single species; and Didelphinae, containing 87 species split between 14 genera. Over one hundred extinct Didelphimorph species have been discovered, though due to ongoing research and discoveries the exact number and categorization is not fixed.[1]