Bovidae Gray, 1821
* Bovidae on Mammal species of the World.
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 South America, Australia and Antarctica, and diverse: members include bison, African Buffalo, water buffalo, antelopes, gazelles, sheep, goats, muskox, and domestic cattle.
The largest bovid, the gaur, weighs well over a ton and stand 2.2 metres high at the shoulder; the smallest, the royal antelope, weighs about 3 kg and stands no taller than a large domestic cat. Some are thick-set and muscular; others are 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 high mountains.
Most members of the family are herbivorous, except most duikers, which are omnivorous. Like other ruminants, bovids have a four-chambered stomach which allows them to digest plant material, such as grass, that cannot be used by many other animals. Such plant material includes much cellulose, and no higher animal can digest this directly. However, ruminants (and some others like kangaroos, rabbits and termites) are able to use micro-organisms living in their gut 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 species tend to have more selective diets, and be browsers rather than grazers. Their upper canine teeth and incisors are missing, and are replaced with a hard, horny pad, that the lower teeth grind against to cut grass or other foliage. The outer pair of teeth in the front of the lower jaw are either considered to be canines, or to be incisors, with the canines missing. The cheek teeth are low-crowned and selenodont, and are separated from the forward teeth by a wide gap, or diastema. The dental formula for bovids is similar to that of other ruminants:
All bovids have four toes on each foot – they walk on the central two (the hooves), while the outer two (the dew-claws) are much smaller and rarely if ever touch the ground. Apart from some domesticated forms, the males in all species have horns, and in many the females do, too. The size and shape of the horns vary greatly, but the basic structure is always a pair of simple bony protrusions without branches, often having a spiral, twisted or fluted form, each covered in a permanent sheath of keratin. The horns of females are usually smaller than those of males, and are sometimes of a different shape. It is theorized that the horns of female bovids evolved for defense against predators.
The bovid family is known through fossils from the early Miocene, around 20 million years ago. The earliest bovids, such as Eotragus, were small animals, somewhat similar to modern gazelles, and probably lived in woodland environments. The bovids rapidly diversified and by the late Miocene, the number of bovid species had greatly expanded. This late Miocene radiation was partly due to the fact that many bovids became adapted to more open, grassland, habitat. There are 78 genera known from the Miocene (compared to 50 today).
Early in their evolutionary history, the bovids split up into two main clades: Boodontia and Aegodontia. This early split between Boodontia (of Eurasian origin) and Aegodontia (of African origin) has been attributed to the continental divide between these landmasses. When these continents were later rejoined, this barrier was removed, and both groups expanded into each other's territory.
The largest number of modern bovids is found in Africa, while substantial but less diverse populations are in Asia and North America. Some scientists has suggested that many bovid species that evolved in Asia could not survive predation by humans arriving from Africa in the late Pleistocene. By contrast, African species had many thousands or a few million years to adapt to the gradual development of human hunting skills. Yet many of the commonly domesticated bovid species (goats, sheep, water buffalo and yak) originated in Asia. This may be because Asian bovids had less fear of humans and were more docile.
The small number of modern American bovids are relatively recent arrivals over the Bering land bridge, but they long predate human arrival.
The bovid family is commonly subdivided into eight subfamilies. Recently, two additional subfamilies have been recognised. The eight traditional subfamilies can be divided into two clades, the Boodontia (with the Bovinae as sole members) and the Aegodontia (composed of all other subfamilies). Some authors do not agree with the high number of subfamilies, although they do recognise these two clades. However, these are treated as subfamilies instead: Bovinae (without change) and Antilopinae (with all of the Aegodontid subfamilies as tribes within it).
Among the eight to ten subfamilies presented here, only some groups have a well-established phylogeny. The Bovinae, for example, are monophyletic and basal; while the Caprinae, Hippotraginae, and Alcelaphinae cluster together consistently. The phylogenetic relationships of the other subfamilies are still unclear or unresolved.
Source: Wikispecies, Wikipedia: All text is available under the terms of the GNU Free Documentation License