下面小编跟大家一起了解托福阅读背景资料短文分享，希望对大家的学习有所帮助、
　　bison是托福阅读非常喜欢的动物之一，今天的专栏跟着老师认识各种各样的bison吧～
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　　下面，一起看看这篇关于Bison的短文吧～读完后记得把本期的生词背熟哦～
　　Bison are large, even-toed ungulates in the genus Bison within the subfamily Bovinae.
　　Two extant and six extinct species are recognized. Of the six extinct species, five became extinct in the Quaternary extinction event. Bison palaeosinensis evolved in the Early Pleistocene in South Asia, and was the evolutionary ancestor of B. priscus (steppe bison), which was the ancestor of all other Bison species. From 2 million years ago to 6,000 BC, steppe bison ranged across the mammoth steppe, inhabiting Europe and northern Asia with B. schoetensacki (woodland bison), and North America with B. antiquus, B. latifrons, and B. occidentalis. The last species to go extinct, B. occidentalis, was succeeded at 3,000 BC by B. bison.
　　Of the two surviving species, the American bison, B. bison, found only in North America, is the more numerous. Although commonly known as a buffalo in the United States and Canada, 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. A third subspecies, the eastern bison (B. b. pennsylvanicus) is no longer considered a valid taxon, being a junior synonym of B. b. bison. References to "woods bison" or "wood bison" from the eastern United States confusingly refer to this subspecies, not B. b. athabascae, which was not found in the region. 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 sometimes fertile offspring calLED beefalo or zubron.
　　The American bison and the European bison (wisent) are the largest surviving terrestrial animals in North America and Europe. They are typical artiodactyl (cloven hooved) ungulates, and are similar in appearance to other bovines such as cattle and true buffalo. They are broad and muscular with shaggy coats of long hair. Adults grow up to 1.8m (5ft 11in) in length for American bison and up to 2.8 metres (9ft 2in) in length for European bison. American bison can weigh from around 400 to 900kg (880 to 1,980lb) and European bison can weigh from 800 to 1,000kg (1,800 to 2,200lb). European bison tend to be taller and heavier than American bison.
　　Bison are nomadic grazers and travel in herds. The bulls leave the herds of females at two or three years of age, and join a herd of males, 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, but formerly had a much larger range, including much of the eastern United States and parts of Mexico. Both species were hunted close to extinction during the 19th and 20th centuries, but have since rebounded; the wisent owing its survival, in part, to the Chernobyl disaster, ironically, as the Chernobyl Exclusion Zone has become a kind of wildlife preserve for wisent and other rare megafauna such as the Przewalski's horse, though poaching has become a threat in recent years. The American Plains bison is no longer listed as endangered, but this does not mean the species is secure. Genetically pure B. b. bison currently number only about 20,000, separated into fragmented herds—all of which require active conservation measures. The Wood bison is on the endangered species list in Canada and is listed as threatened in the United States, though numerous attempts have been made by beefalo ranchers to have it entirely removed from the Endangered Species List.
　　A museum display shows the full skeleton of an adult male American bison
　　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 difference in this case is that what would be the first lumbar vertebra 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.
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　　生词
　　even-toed ungulates 偶蹄类；偶蹄动物（是哺乳动物的一个大型分支。陆生种类四足各有四趾或二趾，趾甲极度特化，呈角质蹄。因每足的蹄甲数为偶数（四或二），故称偶蹄动物。）
　　genus (动植物的)属
　　Bovinae 牛亚科
　　Quaternary extinction event 第四纪灭绝事件（或称冰河时期灭绝事件，是于第四纪发生的大量巨型动物群的灭绝事件，大部份都是在过渡到全新世之间发生的。有些学者会将此次生物集群灭绝看为全新世灭绝事件之一，也有认为是独立事件。古生物学家认为其成因可能是疾病的传播、气候转变、或被人类过度猎杀等。）
　　Early Pleistocene 早更新世（是第四纪冰川更新世的一、个时期）
　　steppe bison 草原野牛
　　B. antiquus 古风野牛（灭绝）
　　B. latifrons 长角野牛（灭绝）
　　B. occidentalis 亚洲野牛（灭绝）
　　buffalo 水牛
　　beefalo 皮弗娄牛（一种由肉用黄牛与北美野牛杂交而成的肉奶兼用型牛）
　　nomadic 游牧的
　　commingle 混合
　　END
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