Mammals are the best known group of the animal kingdom. They are divided into three orders: placental, whose young are born in an advanced state, marsupials, whose young are born in an embryonic stage, their development being completed in their mothers pouch, and montremes, or egg-laying mammals.
Mammals are vertebrates with body hair, mammary glands, and four limbs, which are modified into fins in most aquatic mammals. They breath air and are warm-blooded, which means their internal body temperature remains more or less constant, regardless of the surrounding, external temperature. They have a four chambered heart with an efficient circulatory system.
Mammal Fact For Today