Physical characteristics

Shape, size, and color

Body shape of members of this family varies from relatively small, slender-limbed species such as the gazelles to the massive, stocky wild cattle. The forequarters are either larger than the hind, as in many large species like wild cattle, wildebeest, and tragelaphine antelopes, or the reverse, as in smaller species inhabiting dense tropical forests such as duikers (Cephalophinae).

Bovids encompass an extremely wide size range, starting with the diminutive dwarf antelopes (Neotragus), which weigh as little as 4.5 lb (2 kg) and stand 10-12 in (25-30 cm) at the shoulder, with a total body length of 22-24 in (55-62 cm), and ending with Asian water buffalo (Bubalus bubalis), which weigh as much as 2,600 lb (1,200 kg), and the wild cattle such as gaur (Bos gaurus), which are up to 85 in (220 cm) at the shoulder, and the yak (Bos grunniens), whose total length can reach 128 in (325 cm).

The variety of body coloration of bovids is also extensive, ranging from the predominantly white or very pale, creamy white seen in addax (Addax nasomaculatus) to the purple-black of adult male Indian gaur and the orange-yellow coat of golden takin (Budorcas taxicolor bedfordi). However, most bovids are some shade of brown. The body coloration can consist of a solid shade; in some, the belly is lighter, while in others, the pelage is patterned. In some species, the patterned coloration is for crypsis and camouflage, such as light stripes against a darker ground that help break the body outline. Such a pelage pattern is seen in the aptly named zebra duiker (Cephalophus zebra) and the sitatunga (Tragelaphus spekii). In others such as gemsbok (Oryx gazella), contrasting colors and body markings are used for intraspecific displays. The sexes often are differently colored, with males usually having the darker pelage. Frequently within species, there are also age-specific colorations. For example, for the first few weeks or months after birth, the pelage color of young is quite different from that of adults, such as in the orange-brown coat of young bison (Bison bison), which contrasts to the dark burnt-sienna brown of the adults. In species such as blackbuck (Antilope cervicapra) or sable antelope (Hippotragus niger), adult males are much darker colored than are subadult males and other age-sex classes.

Other distinguishing characteristics

One pair of unbranched horns characterize bovids, except for the unique chousingha (Tetracerus quadricornis) from India, also known as the four-horned antelope. All male bovids have horns, and so do females in several species, although they are almost always smaller. Whether females are horned or not seems to be depend on the degree of intraspecific resource competition, which will be relatively greater in species forming large groups. As Charles Darwin, and later others, argued, horns evolved primarily through sexual selection involving in-traspecific competition, and are used for fighting and display purposes.

Horn shape varies greatly among the Bovidae, from short, sharply pointed horns of steenbok (Raphicerus campestris) to

A mother roan antelope (Hippotragus equinus) nuzzles her newborn. (Photo by Animals Animals ©Jim Tuten. Reproduced by permission.)

the long, spirally twisted horns of tragelaphines to the relatively massive but simple curved horns of water buffalo. Horns are comprised of an inner bone core attached to the frontal bones of the skull, and an outer keratinized sheath, separated by two thin layers of tissue, the epidermis and the dermis. The inner bone core increases in size each year until maturity, when the growth slows or ceases. The outer horn sheath grows each year but is not shed, so the annual sheaths grow inside each other, forming a series of cones stacked one inside the other. The demarcation between each successive year's growth is distinct in some species such as wild sheep (Ovis), and forms a ring where one year's sheath stopped growing and the next began. Counting these annual rings can give a reliable estimate of the animal's age, but this technique does not work for all species, or sometimes not even for both sexes of the same species.

Bovids walk on the their hooves (unguligrade) and all have typical paraxonic limbs, in which two well-developed digits on both front and hind feet, the third and fourth digits, bear the weight of the body. The second and fifth digits are either absent or, more often, small, forming the so-called lateral hooves, or dewclaws. The third and fourth metapodials, the only ones completely present, are fused into a single functional unit sometimes referred to as the cannon bone. Ker-atinous hooves sheath the terminal bone of each toe. Other adaptations of the bovid limb include a reduction in size of the distal end of the ulna, which is also fused to the radius of the fore limb, and a similar reduction of the distal end of the fibula on the hind limb.

The bovid skull lacks a sagittal crest, and the orbits that form a complete circle with a postorbital bar at the rear are located at the sides and toward the top of the head. The lacrimal canals have a single opening within the orbit, and there are often pits or preorbital vacuities in front of the orbit. The dental formula is (I0/3 C0/1 P3/2-3 M3/3) X 2 = 30-32. All species lack both upper incisors and upper canines. The lower canines are usually incisiform (incisor-like), adding to the cropping function of these front teeth. Plants such as grasses and forbs (e.g., herbs and wildflowers) are brought into the mouth by the lips and tongue, where they are severed by the lower incisors pressing against the hard cartilaginous pad of the upper palate, followed by a quick upward jerk of the head. Tougher plants such as shoots of shrubs are severed by the premolars and molars. Depending on diet, the incisors can be wide (spatulate) and relatively uniform in size, as in grazers, or narrower and often of various sizes, as in browsers. There is a large, clearly defined gap (diastema) on the lower jaw between the canine and the first of the premolars. The structure of the premolars and molars depends on the dietary habits. In obligate grazers, they are al-

Brahma cattle (Bos indicus) bred for tolerance to heat, in Costa Rica. (Photo by Animals Animals ©Ken Cole. Reproduced by permission.)

most always high crowned (hypsodont), while in browsers, they are usually low crowned (brachydont). Some mixed grazer-browsers have mesodont molars. In all three types, the enamel of the molars and some premolars is folded into crescent-shaped (selenodont) loops and ridges, which are highly effective for grinding plant material into small particles to aid digestion.

All Bovidae are ruminants, having a four-chambered stomach, and regurgitate and re-chew their food (chew cud) as another means of increasing digestive efficiency.

Female Bovidae have either one or two pairs of functional mammae. Many species of bovids have glands that produce secretions used in intraspecific communication. They are especially common in many of the African antelopes, which use the secretions for marking territorial boundaries.

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