Marsupials

Marsupials are a group of mammals that includes the infraclass Metatheria, distinct from placental mammals (eutherians). They are characterized by a reproductive strategy that typically includes a short gestation followed by continued development of the young outside the womb, usually in a pouch or marsupium. After birth, the underdeveloped neonate crawls to the mother's pouch and attaches to a nipple, where development continues for weeks or months.

Most living marsupials are found in Australia and nearby regions such as New Guinea, but a fossil record indicates an origin that predates the separation of southern continents. A smaller, more ancient lineage persists in the Americas, including the opossums of North and Central America. The diversity of living marsupials is organized into several orders, with the best known including Diprotodontia (kangaroos, wallabies, koalas, possums), Dasyuromorphia (Tasmanian devil, dunnarts, quolls), Peramelemorphia (bandicoots, bilbies), Notoryctemorphia (marsupial moles), and Didelphimorphia (opossums) in the Americas. The Australian-New Guinean region hosts most of the remaining diversity.

Reproduction and growth are central to marsupial biology. After a brief gestation, the young are born very underdeveloped and typically complete their development in a nipple-bearing mammary pouch. Lactation durations vary by species and can extend for several months, allowing continued growth and development outside the uterus.

Conservation concerns affect many species, with habitat loss, invasive predators, and climate change contributing to declines. Some marsupials, such as koalas and certain wallabies and dasyurids, are listed as vulnerable or endangered in parts of their range.