Marsupials are a group of mammals belonging to the infraclass Metatheria, characterized primarily by their unique reproductive process. Unlike placental mammals, marsupials give birth to relatively undeveloped young, called joeys, which then continue their development outside the womb, typically inside a pouch (marsupium) on the mother's belly
. Key characteristics of marsupials include:
- Very short gestation periods; the newborns are tiny, hairless, and underdeveloped at birth
- After birth, the joey climbs to the mother's pouch or skin fold and attaches to a nipple, where it continues to grow and develop while nursing
- The pouch serves to protect the young during this vulnerable stage, though not all marsupials have a fully formed pouch; some have only skin folds or exposed nipples
- Marsupials have an extra pubic bone (epipubic bone) that supports the pouch
- Many marsupials have syndactyly, a condition where some toes are fused or webbed, like in koalas
Marsupials are most diverse and abundant in Australia, New Guinea, and nearby islands, where they make up the majority of native mammals. Well-known Australian marsupials include kangaroos, wallabies, koalas, wombats, and the Tasmanian devil. About 70 species live in the Americas, mainly South and Central America, with the Virginia opossum being the only marsupial found in the United States and Canada
. Examples of marsupials:
- Kangaroos and wallabies (herbivores)
- Koalas (herbivores specialized in eucalyptus leaves)
- Tasmanian devil (carnivore)
- Opossums (omnivores, found in the Americas)
- The extinct Tasmanian tiger (carnivorous marsupial)
In summary, marsupials are mammals distinguished by their early birth of underdeveloped young that complete development externally, usually in a pouch, and they are predominantly native to Australasia and the Americas
