ratite

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ratite

(răt`īt), common and general term for a variety of flightless birds characterized by a flat, raftlike sternum rather than the keeled sternum, designed to support flight muscles, typical of most birds. Once used more technically, ratite, or Ratitae, is today but a loose covering term for a number of bird orders whose members possess such a breast shape. It is generally recognized, however, that the common morphology shared by these assorted birds is the product of a shared adaptation to ground living rather than of a common evolutionary descent. While ratites were formerly thought to be ancestral to the carinates, or flying birds, they are now believed to be forms that have lost adaptation for flight. Indeed, they resemble permanent overgrown chicks with short, stubby wings and soft rather than stiff-vaned flight feathers. This condition, in which animals reach adult size and maturity while maintaining an infantile appearance, is called neoteny. In their own environment, however, the ratites are by no means inferior to other birds. With their strong, heavy legs and reduced toes, they are powerful runners, and their heavy, solid bones are sturdier than the hollow bones of flying birds. The ratites include the Afro-Asian ostrichesostrich,
common name for a large flightless bird (Struthio camelus) of Africa and parts of SW Asia, allied to the rhea, the emu and the extinct moa. It is the largest of living birds; some males reach a height of 8 ft (244 cm) and weigh from 200 to 300 lb (90–135
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 (order Struthioniformes) and their South American counterparts the rheasrhea
, common name for a South American bird of the family Rheidae, which is related to the ostrich. Weighing from 44 to 55 lb (20–25 kg) and standing up to 60 in.
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 (Rheiformes) as well as a number of orders now or recently native to Australia, New Zealand, and New Guinea—the emusemu
or emeu
, common name for a large, flightless bird of Australia, related to the cassowary and the ostrich. There is only one living species, Dromaius novaehollandiae. It is 5 to 6 ft (150–180 cm) tall and a very swift runner.
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 and cassowariescassowary
, common name for a flightless, swift-running, pugnacious forest bird of Australia and the Malay Archipelago, smaller than the ostrich and emu. The plumage is dark and glossy and the head and neck unfeathered, wattled, and brilliantly colored, with variations in the
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 (Casuariiformes); the kiwiskiwi
or apteryx
, common name for the smallest member of an order of primitive flightless birds related to the ostrich, the emu, and the cassowary. The kiwi, named by the Maoris for its shrill, piping call, is most closely related to the extinct moa.
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 (Apterygiformes); the extinct moasmoa
[Maori], common name for an extinct flightless bird of New Zealand related to the kiwi, the emu, the cassowary, and the ostrich. The various species ranged in size from that of a turkey to the 10-ft (3-m) Dinornis giganteus.
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 (Dinornithiformes); the Madagascan elephant birds (Aepyornithiformes); and several other extinct orders. The small, tropical New World tinamoutinamou
, common name for a South American game bird related to the ostrich. It is protectively colored in browns and grays. The females are the aggressors in courtship, and the males incubate the colorful eggs and rear the young.
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 (order Tinamiformes) has a keeled sternum and can fly, but shares some features with the ratites, such as the possession of a specialized bony palate. The flightless penguins are not ratites, since they have neither bony palate nor flat breastbone. In addition, their wings are powerful swim fins, and their chest muscles and sternum are as developed as those of any flying bird. The orders of ratites are classified in the phylum ChordataChordata
, phylum of animals having a notochord, or dorsal stiffening rod, as the chief internal skeletal support at some stage of their development. Most chordates are vertebrates (animals with backbones), but the phylum also includes some small marine invertebrate animals.
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, subphylum Vertebrata, class Aves.