Check us out at www.tutorvista.com Mammals (formally Mammalia) are a class of vertebrate, air-breathing animals whose females are characterized by the possession of mammary glands while both males and females are characterized by sweat glands, hair and/or fur, three middle ear bones used in hearing, and a neocortex region in the brain. Mammals are divided into three main infraclass taxa depending how they are born. These taxa are: monotremes, marsupials and placentals. Except for the five species of monotremes (which lay eggs), all mammal species give birth to live young. Most mammals also possess specialized teeth, and the largest group of mammals, the placentals, use a placenta during gestation. The mammalian brain regulates endothermic and circulatory systems, including a four-chambered heart. There are approximately 5400 species of mammals, distributed in about 1200 genera, 153 families, and 29 orders(though this varies by classification scheme). Mammals range in size from the 3040 millimeter (1- to 1.5-inch) Bumblebee Bat to the 33-meter (108-foot) Blue Whale. Mammals are divided into two subclasses: the Prototheria, which includes the oviparous monotremes, and the Theria, which includes the placentals and live-bearing marsupials. Most mammals, including the six largest orders, belong to the placental group. The three largest orders, in descending order, are Rodentia (mice, rats, porcupines, beavers, capybaras, and other gnawing mammals), Chiroptera (bats), and
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