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MAMMALS.
From Wikipedia, the free encyclopaedia
Mammals are a class of vertebrate animals whose name is derived from their distinctive feature, mammary glands, with which they feed their young. They are also characterized by the possession of sweat glands, hair, three middle ear bones used in hearing, and a neocortex region in the brain. Except for the five species of monotremes (which lay eggs), all mammals 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 5,400 species of mammals, distributed in about 1,200 genera, 153 families, and 29 orders[1] (though this varies by classification scheme). Mammals range in size from the 30-40-millimetre (1.2-1.6 in) Bumblebee Bat to the 33-metre (110 ft) Blue Whale. The mammals are divided into two subclasses, the prototheria, which includes the egg-laying monotremes, and the theria, which includes the live-bearing marsupials and placentals. Most mammals, including the six largest orders, belong to the placental group. The three largest orders, in descending order, are Rodentia (mice, rats, and other small, gnawing mammals), Chiroptera (bats), and Soricomorpha (shrews, moles and solenodons). The next three largest orders include the Carnivora (dogs, cats, weasels, bears, seals, and their relatives), the Cetartiodactyla (including the even-toed hoofed mammals and the whales) and the Primates to which the human species belongs. The relative size of these latter three orders differs according to the classification scheme and definitions used by various authors. Phylogenetically, Mammalia is defined as all descendants of the most recent common ancestor of monotremes (e.g., echidnas and platypuses) and therian mammals (marsupials and placentals). The mammalian line of descent diverged from the reptile line at the end of the Carboniferous period. The majority of reptiles would evolve into modern-day reptiles and birds, while the synapsid branch led to mammals. The first true mammals appeared in the Jurassic period. Modern mammalian orders appeared in the Palaeocene and Eocene epochs of the Palaeogene period.
From Wikipedia, the free encyclopaedia
Mammals are a class of vertebrate animals whose name is derived from their distinctive feature, mammary glands, with which they feed their young. They are also characterized by the possession of sweat glands, hair, three middle ear bones used in hearing, and a neocortex region in the brain. Except for the five species of monotremes (which lay eggs), all mammals 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 5,400 species of mammals, distributed in about 1,200 genera, 153 families, and 29 orders[1] (though this varies by classification scheme). Mammals range in size from the 30-40-millimetre (1.2-1.6 in) Bumblebee Bat to the 33-metre (110 ft) Blue Whale. The mammals are divided into two subclasses, the prototheria, which includes the egg-laying monotremes, and the theria, which includes the live-bearing marsupials and placentals. Most mammals, including the six largest orders, belong to the placental group. The three largest orders, in descending order, are Rodentia (mice, rats, and other small, gnawing mammals), Chiroptera (bats), and Soricomorpha (shrews, moles and solenodons). The next three largest orders include the Carnivora (dogs, cats, weasels, bears, seals, and their relatives), the Cetartiodactyla (including the even-toed hoofed mammals and the whales) and the Primates to which the human species belongs. The relative size of these latter three orders differs according to the classification scheme and definitions used by various authors. Phylogenetically, Mammalia is defined as all descendants of the most recent common ancestor of monotremes (e.g., echidnas and platypuses) and therian mammals (marsupials and placentals). The mammalian line of descent diverged from the reptile line at the end of the Carboniferous period. The majority of reptiles would evolve into modern-day reptiles and birds, while the synapsid branch led to mammals. The first true mammals appeared in the Jurassic period. Modern mammalian orders appeared in the Palaeocene and Eocene epochs of the Palaeogene period.