Les Phalangeriformes forment un sous-ordre qui regroupe des petits marsupiaux appelés en français couscous, phalangers, Acrobates, souris à miel ou encore planeurs dans le cas de certains écureuils volants. Ils sont dits aussi parfois « possums », wyuldas, trioks... Ce sous-ordre des mammifères est divisé en deux superfamilles.
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, wallabies, the koala, possums (including gliding possums), opossums, wombats and the Tasmanian devil. Less well-known species of marsupials include the numbat, bandicoots, bettongs, the bilby and quolls.
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.