Mammal

Most mammals are land dwellers, living in such diverse habitats as the bare areas of deserts, tundras, and mountains, and the forested areas of the tropics. Two placental orders and several genera of a third order are aquatic. Monotremes are restricted to Australia, Tasmania, and New Guinea. Marsupials are dominant in the same region as monotremes, but two groups of marsupials are native to the Americas. Two orders of placental mammals—bats and rodents—are represented in the fauna of all continents except Antarctica. In Australia the placentals are represented by a few species of rats, the wild dog (or dingo), and a few species of bats; the dingo probably was introduced by human beings.

The primates are native to most tropical and subtropical regions except those of Australia. Insectivores, rabbits, hares, pikas, and even-toed ungulates are native to all continents except Australia and Antarctica, and the odd-toed ungulates are native to Eurasia, Africa, and South America. The sloths, armadillos, tamandua, and anteaters are found only in the Americas. The colugos are restricted to the Malay Peninsula, Indonesia, Borneo, and the Philippines. The pangolins are found in Africa and in Asia. The aardvarks are exclusively African. Two small orders, the elephants and hyraxes, are represented only in the faunas of Asia and Africa.

Scientific classification: Mammals are classified differently by many zoologists. The class Mammalia is usually divided into three subclasses: the Monotremata (Prototheria) or egg-laying mammals, the Marsupialia (Metatheria) or marsupial mammals, and the Placentalia (Eutheria) or placental mammals.

The Monotremata subclass has one order, which includes the platypus and spiny anteaters of Australia. Marsupials are split into seven orders: (1) Didelphimorphia, American opossums; (2) Pancituberculata, American shrew opossums; (3) Microbiotheria, colocolos (or Monito del Monte) from Chile and Argentina; (4) Dasyuromorphia, carnivorous Australasian mammals, including the numbat; (5) Peramelemorphia, bandicoots and bilbies from Australasia; (6) Notoryctemorphia, two species of marsupial mole from Australia; and (7) Diprotodontia, koala, wombat, opossums, kangaroos, and wallabies.

The placentals include most mammalian species, usually divided into 18 orders: (1) Insectivora, including small mammals such as moles, shrews, tenrecs, and hedgehogs; (2) Dermoptera, the colugos, or so-called flying lemurs; (3) Chiroptera, the bats; (4) Carnivora, including the cats, viverrids (civets and mongooses), dogs (including wolves, foxes, and coyotes), hyenas, raccoons, bears, and mustelids (weasels, martens, otters, badgers, and skunks), seals, sea lions, and walrus; (5) Macroscelidea, the elephant shrews; (6) Primates, including the lemurs, lorises, tarsiers, monkeys, apes, and humans; (7) Xenarthra, including armadillos, sloths, and the three anteaters of the Americas; (8) Pholidota, the pangolins; (9) Tubulidentata, the aardvark; (10) Rodentia, including squirrels, beavers, pocket gophers, pocket mice, rats, mice, mole rats, dormice, jerboas, porcupines, guinea pigs, and chinchillas; (11) Lagomorpha, including rabbits, hares, and pikas; (12) Sirenia, including the manatees and dugong; (13) Cetacea, the whales and dolphins; (14) Hyracoidea, the hyraxes; (15) Artiodactyla (even-toed ungulates), including pigs, hippopotamuses, camels, llamas, chevrotains, deer, giraffes, the pronghorn, cattle, antelopes, goats, and sheep; (16) Perissodactyla (odd-toed ungulates), including horses, rhinoceroses, and tapirs; (17) Scandentia, the tree shrews; and (18) Proboscidea, the elephants.