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an individual of the class Mammalia, a division of vertebrates, including all that possess hair and suckle their young.
true placental mammals which develop chorion, amnion, yolk sac and allantois, all of which contribute to the placenta. Called also placental mammals.
marsupials including kangaroos, opossums which are born after a brief period of development and spend a long time being nurtured by the mother, usually in a pouch or marsupium.
see eutherian mammals (above).
monotremes, the egg-laying mammals.