Marsupials are an infraclass of mammals living primarily in the Southern Hemisphere; a distinctive characteristic, common to most species, is that the young are carried in a pouch. Well-known marsupials include kangaroos, the koala, possums, opossums, wombats and the Tasmanian devil. Marsupials represent the clade originating with the last common ancestor of extant metatherians. Like other mammals in the Metatheria, they are characterized by giving birth to relatively undeveloped young, often residing in a pouch with the mother for a certain time after birth. Close to 70% of the 334 extant species occur in Australia, New Guinea, and nearby islands, with the remaining 100 found in the Americas, primarily in South America, but with 13 in Central America, and one in North America, north of Mexico.
A possum (plural form: possums) is any of about 70 small to medium-sized arboreal marsupial species native to Australia, New Guinea, and Sulawesi (and introduced to New Zealand and China).
Possums are quadrupedal diprotodont marsupials with long thick tails. The smallest possum, indeed the smallest diprotodont marsupial, is the Little Pygmy Possum with an adult head-body length of 70mm and a weight of 10g. The largest is the Bear Cuscus that may exceed 7 kg. Possums are typically nocturnal and at least partially arboreal. The various species inhabit most vegetated habitats and several species have adjusted well to urban settings. Diets range from generalist herbivores or omnivores (the Common Brushtail possum) to specialist browsers of eucalyptus (Greater Glider), insectivores (Mountain Pygmy Possum) and nectar-feeders (Honey Possum).