Dichotomous keys to the mammals of the South by order

The opossum belongs to one of the seven orders of mammals commonly known as “marsupials,” referring to the abdominal pouch or marsupium where the young are carried. However, only about half of all marsupials actually possess a permanent pouch. Considered to be a primitive marsupial order, Didelphimorphia is restricted to the New World (Gardner 1993). The sole family in the order, Family Didelphidae, is represented by 15 genera and 66 species that are distributed throughout South, Central, and North America (Nowak 1999). Baker et al. (2003) report one species in North America, the Virginia opossum (Didelphis virginiana).