Many are covered with hair or fur and all are warm blooded, having evolved complex biochemical and physiological mechanisms for maintaining body temperature. Female mammals have mammary glands which supply milk for the young animals, and the young are born live, rather than being laid in eggs Parental care is advanced in this group of animals, reaching its climax in the primates, which include our own species.
Mammals live in all kinds of habitats from the tropics to the polar regions.
Mammals range in size from the smallest shrews that may be only 2 inches long up to the huge elephants and whales. The blue whale can be 100 feet long. Some mammals are fierce predators adapted for hunting, while others like deer and gazelles are shy vegetarians. Each species shows adaptations for its lifestyle - for example meat eaters have sharp teeth to tear through their victims flesh, while vegetarians have grinding teeth to break tough plant tissues. Mammals are grouped according to a number of criteria.