What is the definition of "marsupials"?

Marsupials are nonplacental mammals that do not fully develop during gestation. Instead they complete their development within the pouch of the mother after birth. Marsupials are born while still in the embryonic stage, and they climb to the mother's pouch where her teats are located.

Animals that belong to the marsupial family include kangaroos, wombats, koalas and sugar gliders. Marsupials are most prevalent in Australia and South America, with the opossum being the only marsupial that is native to the U.S.

North America was once a common area to find marsupials in the Mesozoic Era, but they became almost nonexistent during the late Tertiary Period.