Bovid

A bovid (family Bovidae) is any of almost 140 species of cloven-hoofed ruminant mammal at least the males of which bear characteristic unbranching horns covered in a permanent sheath of keratin.

The family is widespread, being native to Asia, Africa, Europe and North America, and diverse: members include bison, African buffalo, water buffalo, antelopes, gazelles, sheep, goats, muskoxen, and domestic cattle.

Characteristics

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 microorganisms 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. However, 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 or

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 unique horn structure is the only unambiguous morphological feature of bovids that distinguish them from other pecorans. Male horn development has been linked to sexual selection, while the presence of horns in females is likely due to natural selection. 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 or to express territoriality, as non-territorial females who are able to use crypsis for predator defense often do not have horns. There are 78 genera known from the Miocene (compared to 50 today).

Early in their evolutionary history, the bovids split 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.

Taxonomy

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.

Classification

References

External links