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American Bison.
Scientific classification

A bovid is any of almost 140 species of cloven-hoofed mammals belonging to the family Bovidae. The family is widespread, being native to all continents except Australia and Antarctica, and diverse: members include buffalo, bison, antelopes, gazelles, and both wild and domesticated cattle, sheep, goats, and water buffalo.

The largest bovids weight well over a tonne and stand 2 metres high at the shoulder; the smallest weigh about 3 kilos and stand no taller than a large domestic cat. Some are thick-set and muscular, others lightly built with small frames and long legs. Many species congregate into large groups with complex social structures, but others are mostly solitary. Within their extensive range, they occupy a wide variety of habitat types, from desert to tundra and from thick tropical forest to cliff-faces.

All members of the family are herbivorous (although a few will take a small amount of meat if it is available), and all have a four-chambered stomach which allows most of them to digest foods that are too low in nutriment for many other animals, notably grasses. No animal is able to directly digest cellulose: like (for example) kangaroos and termites, bovids rely on stomach bacteria to break down cellulose by fermentation.

Because of the size and weight of their complex digestive systems, many bovids have a solid, stocky build; the more gracile members of the family tend to have more selective diets, and be browsers rather than grazers. Their canine teeth are either missing or else modified to act as extra incisors. All bovids have a two-toed hoof. All males (and many females) have horns; the size and shape varies greatly but the basic structure is always a single bony protrusion without branches and covered in a sheath of keratin.

The family is known through the fossil record from the early Miocene. The largest number of modern bovids are found in Africa, with substantial but less diverse populations in Asia and North America. It is thought that many of the bovid species which evolved in Asia were unable to survive the sudden advent of a new and unfamiliar predator when humans first emerged from Africa in the late Pleistocene, the African species, on the other hand, had many thousands of years, perhaps a few millions, in which to gradually adapt to the equally gradual development of human hunting skills. It is notable that many of the commonly domesticated bovid species—goats, sheep, water buffalo, the Yak—are of Asian origin: it is believed that the Asian bovids had less fear of humans and were more docile.

Mountain Goat.

The small number of modern American bovids are relatively recent arrivals over the Bering Land Bridge. All of the large grazing animals native to North America died out immediately after the arrival of the Clovis people about 12,000 years ago. This left a number of ecological niches vacant, and the ancestors of the modern American Bison, Mountain Goat and American Bighorn Sheep moved in to occupy them.