A marsupial is a mammal whose young are born in an extremely immature state. The newborn undergoes most of its development attached to one of its mother's nipples and nourished by her milk. Females of most
marsupials have pouch, called the marsupiam, which protects the babies. There are about 270 species of marsupials, all of which live in either the Americas or Australasia. They include kangaroos, koalas and opossums. Kangaroos are the largest marsupials - most male red kangaroos stand about 6 feet (1.8 m) tall. The smallest marsupials are the shrew-like ningauis, weighing only about 3 grams. Marsupials inhabit many different environments, including forests, plains and deserts.