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mammal
Columbia Encyclopedia entry: mammal
Mammal, an animal of the highest class of vertebrates, the Mammalia. The female has mammary glands, which secrete milk for the nourishment of the young after birth. In the majority of mammals the body is partially or wholly covered with hair; the heart has four chambers, and only the left aortic arch is present; and a muscular diaphragm separates the chest from the abdominal cavity. Mammals are warm-blooded; that is, they have a relatively constant body temperature independent of the temperature of their surroundings. The mature red blood cells (erythrocytes) usually lack a nucleus. Except for the egg-laying monotremes (the platypus and the echidna, or spiny anteater), mammals give birth to live young. A marsupial is born in a more undeveloped state than the young of other mammals, although all are relatively helpless at birth. In some marsupials and in higher mammals the young receive prenatal nourishment through a placenta. The order Carnivora, or flesh-eating animals, includes terrestrial families such as the cat, dog, and bear as well as the aquatic seal, sea lion, and walrus. Other aquatic mammals are the whale, porpoise, and dolphin of the order Cetacea and the manatee and dugong of the order Sirenia. Unusual adaptations are also found in the bat (order Chiroptera); in the elephant (order Proboscidea); in the sloth, armadillo, and anteater (order Edentata); and in the beaver, woodchuck, porcupine, and squirrel (order Rodentia). The order Insectivora includes the shrew and the mole. There are two groups of ungulates, or hoofed mammals: most members of the order Perissodactyla, including the horse and the rhinoceros, are odd-toed, with the third digit the largest; those of the order Artiodactyla, including the deer, antelope, camel, pig, and cow, are even-toed, with the third and fourth digits symmetrical and functional. Humans, monkeys, apes, and lemurs belong to the order Primates. Some remains of mammals are identified as from the Jurassic period of the Mesozoic era; the group became diversified in the Tertiary period of the Cenozoic era.

See E. P. Walker et al., Mammals of the World (2 vol., rev. ed. 1968); S. Anderson, ed., Simon & Schuster's Guide to Mammals (1984); G. B. Corbett and J. E. Hill, World List of Mammalian Species (1986); H. H. Genoways, ed., Current Mammalogy (2 vol., 1987–89).

The Columbia Encyclopedia. Copyright © 2001-09 Columbia University Press. All rights reserved.

Wikipedia search results for: Mammal
From Wikipedia, the free encyclopedia
Mammals 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 and/or fur, three middle ear bones used in hearing, and a neocortex region in the brain. Mammal are air-breathing animals. 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, 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...more »
Columbia Encyclopedia search results: mammal
Results 1 - 10  of 244
  • dolphin, aquatic mammal

    Dolphin, aquatic mammal, any of the small toothed whales of the family Delphinidae, numbering more than 50 species. These include the true, or beaked, dolphins, the killer whale, the pilot wha...

  • mammary gland

    Mammary gland, organ of the female mammal that produces and secretes milk for the nourishment of the young. A mammal may have from 1 to 11 pairs of mammary glands, depending on the species. Ge...

  • hyrax

    Hyrax, name for rabbit-sized mammals of Africa and SW Asia comprising the family Procavidae. Although rodentlike in appearance, hyraxes are hoofed mammals, or ungulates (see Chordata), most cl...

  • platypus

    Platypus, semiaquatic egg-laying mammal, Ornithorhynchus anatinus, of Tasmania and E Australia. Also called duckbill, or duckbilled platypus, it belongs to the order Monotremata (see monotreme...

  • seal, in zoology

    Seal, carnivorous aquatic mammal with front and hind feet modified as flippers, or fin-feet. The name seal is sometimes applied broadly to any of the fin-footed mammals, or pinnipeds, includin...

  • hair

    Hair, slender threadlike outgrowth from the skin of mammals. In some animals hair grows in dense profusion and is called fur or wool. Although all mammals show some indication of hair formatio...

  • shrew

    Shrew, common name for the small, insectivorous mammals of the family Soricidae, related to the moles. Shrews include the smallest mammals; the smallest shrews are under 2 in. (5.1 cm) long, e...

  • walrus

    Walrus, marine mammal, Odobenus rosmarus, found in Arctic seas. Largest of the fin-footed mammals, or pinnipeds (see seal), the walrus is also distinguished by its long tusks and by cheek pads...

  • rhinoceros

    Rhinoceros, massive hoofed mammal of Africa, India, and SE Asia, characterized by a snout with one or two horns. The rhinoceros family, along with the horse and tapir families, forms the order...

  • hoof

    Hoof, horny epidermal casing at the end of the digits of an ungulate (hoofed) mammal. In the even-toed ungulates, such as swine, deer, and cattle, the hoof is cloven; in the odd-toed ungulates...

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