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The pronghorn (''Antilocapra americana'') is a species of artiodactyl mammal indigenous to interior western and central North America. Though not an antelope, it is often known colloquially in North America as the prong buck, pronghorn antelope, ''cabri'' (native American), or simply antelope because it closely resembles the true antelopes of the Old World and fills a similar ecological niche due to parallel evolution..〔Farb, Peter (1970). ''Ecology''. Time Life Books. pp. 126, 136〕 It is the only surviving member of the family Antilocapridae. During the Pleistocene period, about 12 antilocaprid species existed in North America.〔Smithsonian Institution. North American Mammals: (Pronghorn ''Antilocapra americana'' )〕 Three other genera existed when humans entered North America (''Capromeryx'', ''Stockoceros'' and ''Tetrameryx''), but are now extinct. ==Description== Pronghorns have distinct white fur on their rumps, sides, breasts, bellies, and across their throats. Adult males are long from nose to tail, stand high at the shoulder, and weigh . The females are the same height as males, but weigh . The feet have two hooves, with no dewclaws. Their body temperature is 38 °C (100 °F).〔〔Mammals of Texas: (Pronghorn ) Last retrieved 24 October 2013〕〔(''Antilocapra americana'' ). Animal Diversity Web. Last retrieved 24 October 2013〕〔AnAge: (''Antilocapra americana'' )〕 The orbits (eye sockets) are prominent and set high on the skull, with never an anteorbital pit. Their teeth are hypsodont, and their dental formula is: Each "horn" of the pronghorn is composed of a slender, laterally flattened blade of bone that grows from the frontal bones of the skull, forming a permanent core. As in the Giraffidae, skin covers the bony cores, but in the pronghorn, it develops into a keratinous sheath which is shed and regrown on an annual basis. Unlike the horns of the family Bovidae, the horn sheaths of the pronghorn are branched, each sheath possessing a forward-pointing tine (hence the name pronghorn). Males have a horn sheath about (average ) long with a prong. Females have smaller horns that range from (average ) and sometimes barely visible; they are straight and very rarely pronged.〔 Males are further differentiated from females in having a small patch of black hair at the angle of the mandible. Pronghorns have a distinct, musky odor. Males mark territory with a preorbital scent gland which is located on the sides of the head.〔 They also have very large eyes with a 320° field of vision. Unlike deer, pronghorns possess a gallbladder. The pronghorn is the fastest land mammal in the Western Hemisphere, being built for maximum predator evasion through running. The top speed is very hard to measure accurately and varies between individuals; it can run 35 mph for 4 mi (56 km/h for 6 km), 42 mph for 1 mi (67 km/h for 1.6 km), and 55 mph for 0.5 mi (88.5 km/h for .8 km).〔 It is often cited as the second-fastest land animal, second only to the cheetah. It can, however, sustain high speeds longer than cheetahs.〔 University of Idaho zoologist John Byers has suggested the pronghorn evolved its running ability to escape from extinct predators such as the American cheetah, since its speed greatly exceeds that of extant North American predators.〔 Compared to its body size, the pronghorn has a large windpipe, heart, and lungs to allow it to take in large amounts of air when running. Additionally, pronghorn hooves have two long, cushioned, pointed toes which help absorb shock when running at high speeds.〔(【引用サイトリンク】title=Pronghorn - San Diego Zoo Animals )〕 They also have an extremely light bone structure and hollow hair. Pronghorns are built for speed, not for jumping. Their ranges are sometimes affected by sheep ranchers' fences. However, they can be seen going under fences, sometimes at high speed. For this reason, the Arizona Antelope Foundation and others are in the process of removing the bottom barbed wire from the fences, and/or installing a barbless bottom wire. The pronghorn has been observed to have at least 13 distinct gaits, including one reaching nearly per stride.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「pronghorn」の詳細全文を読む スポンサード リンク
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