Physical characteristics

Bodies range from a rather slender build, in the genus Trichys, to a clumsy and stocky build, in the genus Hystrix. The tail is very short in some species, but can reach around half the head-body length in others. Eyes and external ears are generally small, with a poor sense of sight but a sharp sense of hearing. Nostrils are usually S-shaped, with a sharp sense of smell. The upper lip is cleft, and the tip of the nose is stubbed and covered with velvety hairs. Large, chisel-shaped lower and upper incisor teeth do not have longitudinal grooves and grow throughout life; molars are rooted and have irregular enamel folds that are rapidly worn down.

The skull is long and sometimes inflated with air chambers over the rostrum and top of head. The infraorbital foramen (lower orbital cavity in upper jawbone) is unusually enlarged, resulting in portions of masseter (chewing) muscle being penetrated through it, thus enabling muscles to adhere to the frontal side surface of the upper jawbone (called hys-tricomorphous). The lower jaw is hystricognathous. Features (generally called postorbital processes) possibly evolved to en large chewing volume and to allow animals to smell underground bulbs.

Both forelimbs and hind limbs are short and heavily built; as a result, Old World porcupines are excellent diggers and sometimes construct their own burrows. On the two fore-limbs, each foot has four well-developed clawed digits and one thumb, which is regressed and externally visible only by nail and thumb pad; each of two hind feet has five functional digits. Claws are short and soles of feet are smooth, naked, and fitted with pads. When walking or running, the entire sole of the foot touches the ground. They are able to swim.

The most characteristic physical features are the quills, spines, and bristles. The head, body, and (in some species) tail are covered by barb-less spines, which are thick, stiff, sharp modified hairs, as much as 13.8 in (35 cm) in length. Spine coloration is brownish or blackish, often with conspicuous white bands around them. All spines lack the barbules that characterize spines of New World porcupines. Longest spines tend to be found on rump and shortest on cheeks. In genus Trichys, for example, spines are short, flattened, and not especially well developed. In genus Hystrix, in contrast, spines develop into hollow quills that reach 7.9 in (20 cm) in length.

Spines vary considerably among species but can be roughly classified into seven groups: (1) stiletto-like quills that are stiff, flattened, with sharp points and longitudinal grooves, which cover most of body; (2) spikes that are thick, inflexible, and

A South African porcupine (Hystrix africaeaustralis) eats gemsbok cucumbers. (Photo by Clem Haagner. Bruce Coleman, Inc. Reproduced by permission.)

with sharp points; (3) bristle-like quills (also called tactile bristles) that are flexible toward the ends, with a round cross section and sharp points; (4) rattling cups that are hollow, capsule-like structures fastened on the end of tail by a thin stem; (5) platelet bristles that are hollow, flattened, yellowish-white at tail end, with shafts that enlarge at regular intervals; (6) brush-type bristles that are flattened, smooth bristles at tail end that look like narrow parchment strips; and (7) mane bristles that are tufts of hair on head and neck.

Normally, quills lie flat and point to the rear. When the animal is threatened or showing aggression, quills can be raised instantly. Hind feet are usually then stamped and quills shaken with a rattling sound (except for Trichys), which serves as a warning to potential predators. If threat continues, the porcupine may charge backwards or sideways into predator with attempt to strike intruder with quills. Quills are loosely attached but cannot be projected. They penetrate flesh and stick readily. No poison is carried; however, bacteria on quills can infect, and sometimes kill, the victim if the puncture wound is deep enough. The area with detached quills will grow back new quills. Some species possess coarse, flat spines that form an erectable crest on necks and tops of heads.

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