Marsupials are mammals in which the female typically has a pouch in which it rears its young through early infancy.
They differ from placental mammals (Placentalia) in their reproductive traits.
The early birth of marsupials removes the developing young much sooner than in placental mammals, and marsupials have not needed to develop a complex placenta to protect the young from its mother's immune system.
Early birth places the tiny newborn marsupial at greater risk, but significantly reduces the risks associated with pregnancy, as there is no need to carry a large fetus to full-term in bad seasons.
There are about 334 species of marsupials, over 200 of them native to Australia and nearby islands to the north.