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Bison or buffalo are large, even-toed ungulates in the genus ''Bison'' within the subfamily Bovinae. Two extant and four extinct species are recognized. Of the four extinct species, three were North American: ''Bison antiquus'', ''B. latifrons'', and ''B. occidentalis''. The fourth, ''B. priscus'', ranged across steppe environments from Western Europe, through Central Asia, and onto North America. Of the two surviving species, the American bison, ''B. bison'', found only in North America, is the more numerous. Although sometimes referred to historically as a "buffalo", it is only distantly related to the true buffalo. The North American species is composed of two subspecies, the plains bison, ''B. b. bison'', and the wood bison, ''B. b. athabascae'', which is the namesake of Wood Buffalo National Park in Canada. The European bison ''B. bonasus'', or wisent, is found in Europe and the Caucasus, reintroduced after being extinct in the wild. While all bison species are classified in their own genus, they are sometimes bred with domestic cattle (genus ''Bos'') and produce fertile offspring called beefalo or zubron. ==Description== The American bison and the European bison (wisent) are the largest terrestrial animals in North America and Europe. Bison are good swimmers and can cross rivers over half a mile (800 meters) wide. They are nomadic grazers and travel in herds. The bulls leave the herds of females at two or three years of age, and join a male herd, which are generally smaller than female herds. Mature bulls rarely travel alone. Towards the end of the summer, for the reproductive season, the sexes necessarily commingle. American bison are known for living in the Great Plains. Both species were hunted close to extinction during the 19th and 20th centuries, but have since rebounded. The American plains bison is no longer listed as endangered, but the wood bison is on the endangered species list in Canada.〔(【引用サイトリンク】title=U.S. ''Fish and Wildlife Service Species Report'' )〕 Although superficially similar, physical and behavioural differences exist between the American and European bison. The American species has 15 ribs, while the European bison has 14. The American bison has four lumbar vertebrae, while the European has five.〔''The Penny Cyclopædia of the Society for the Diffusion of Useful Knowledge'' by Society for the Diffusion of Useful Knowledge (Great Britain), published by C. Knight, 1835〕 (The difference in this case is that what would be the first lumbar vertebra in wisent has ribs attached to it in American bison and is thus counted as the 15th thoracic vertebra, compared to 14 thoracic vertebrae in wisent.) Adult American bison are less slim in build and have shorter legs. American bison tend to graze more, and browse less than their European relatives. Their anatomies reflect this behavioural difference; the American bison's head hangs lower than the European's. The body of the American bison is typically hairier, though its tail has less hair than that of the European bison. The horns of the European bison point through the plane of their faces, making them more adept at fighting through the interlocking of horns in the same manner as domestic cattle, unlike the American bison, which favours butting. American bison are more easily tamed than their European cousins, and breed with domestic cattle more readily. 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「bison」の詳細全文を読む スポンサード リンク
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