"The Virginia Opossum, the only marsupial found north of Mexico, is an adaptable omnivore at home on the ground and in the trees. Opossums prefer forested habitats, but they are quite successful even in urban areas. They are active at night, year-round: in freezing weather, an unlucky opossum can lose its ear-tips and the end of its tail to frostbite. Like all marsupials, opossums give birth to tiny, undeveloped young. The embryos develop in the mother's womb for less than two weeks, then the newborn opossums crawl from the birth canal to the mother's pouch, where they fasten tight to a nipple. They stay there, attached to the nipple, for 55 or 60 days. A female opossum usually has 13 nipples, and litters are usually smaller than that, but a baby that cannot attach to a nipple dies. After about 60 days the young opossums leave the pouch, but they stay close to their mother—sometimes riding on her back when they are out at night—and nurse for another month or more."
Links:Mammal Species of the WorldClick here for The American Society of Mammalogists species account
Original description: Kerr, R., 1792. The animal kingdom, or zoological system, of the celebrated Sir Charles Linnaeus. Class I. Mammalia, p.193. London, 651 pp.