Mammals are a class of vertebrates characterised by warm-blood, hairy bodies, a four-chambered heart, a single jaw bone, sweat glands and - in females - mammary glands for suckling young. Some mammals, such as naked mole rats and whales have lost some or all of their hair. Almost all mammals give birth to live young, but there are a few that lay eggs. These are known as monotremes, and include the platypus.
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Bearing live young comes at a cost worth paying.
The secret to mammalian dominance lies in their warm-bloodedness.
Anteaters and sloths are native to the Americas. There are 10 living species in this order, including the tamanduas, two-toed sloths and three-toed sloths..
Bats are the only mammals that truly fly, rather than just gliding. The bats are very numerous, there being well over 900 recognised species.
The Carnivora is an order of mammals descended from carnivorous ancestors. Although most of the living Carnivora are indeed meat-eaters, some are omnivorous, and the giant panda is largely vegetarian.
Dugongs and manatees, said to be the basis for the mermaid myths, are enormous aquatic mammals that can weigh over a tonne. Over time, their bodies have evolved to become streamlined and they have lost their hind limbs as part of this process.
The even-toed ungulates have two weight-bearing toes on each foot, and may have lost the other toes entirely (as in antelope), or have another two much smaller toes (as in pigs). Hippopotamuses, camels and giraffes are all Artiodactyls..
Hares, rabbits and pikas all belong to the mammalian order lagomorpha. They are similar to large rodents and were once considered part of the same order.
The Diprotodontia is an order of marsupial mammals which includes all the most familiar Australian animals: kangaroos, wallabies, possums, koalas and wombats. Most diprotodontids are herbivorous, although some eat insects and nectar, and a few extinct ones were carnivores..
The Primates is an order of mammals with features characteristic of tree-living ancestors, even in those species that now live on the ground. Lemurs, lorises, bush-babies, monkeys, apes and humans are all primates.
The rodents is the largest of the mammalian orders, with over 2,000 species in it. Familiar rodents include mice, rats and squirrels, but animals such as the porcupine, the beaver and the agouti are also rodents.
Whales, dolphins and porpoises belong to the order Cetacea. These are aquatic mammals that have streamlined bodies evolved for swimming.
Mammals (formally Mammalia) are a class of vertebrate animals whose females are characterized by the possession of mammary glands while both males and females are characterized by sweat glands, hair, 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 5,400 species of mammals, distributed in about 1,200 genera, 153 families, and 29 orders (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.
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, 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). This means that some extinct groups of "mammals" are not members of the crown group Mammalia, even though most of them have all the characteristics that traditionally would have classified them as mammals. These "mammals" are now usually placed in the unranked clade Mammaliaformes.
The mammalian line of descent diverged from an amniote line at the end of the Carboniferous period. One line of amniotes would lead to reptiles, while the other would lead to synapsids. According to cladistics, mammals are a sub-group of synapsids. Although they were preceded by many diverse groups of non-mammalian synapsids (sometimes misleadingly referred to as mammal-like "reptiles"), the first true mammals appeared in the Triassic period. Modern mammalian orders appeared in the Palaeocene and Eocene epochs of the Palaeogene period.
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Class : Mammal (Mammalia)
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