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.