The 11 species (3 genera) of this family are found in Africa and Asia.
Like their New World equivalents, the North American porcupines, Old World porcupines are large, heavyset, slow-moving animals that rely on their imposing quills for defense rather than on speed or agility. The largest hystricids may exceed 25 kg in weight; others weigh a kilogram or two. Their heads are massive and broad. The ears are generally small, as are the eyes. The tail is very short in some species, but it reaches around half the head-body length in others. Both forelimbs and hindlimbs are short and heavily built. The forefeet have 5 digits, but the thumb is reduced in size. The hindfeet have five functional digits. The claws are short. Hystricids are plantigrade, that is, they place the full sole of the foot on the ground when they walk.
The pelage of hystricids varies considerably species to species. All have spines of some sort, but their spines lack the barbules that characterize the spines of New World porcupines. In Trichys, for example, the spines are short, flattened, and not especially well developed. In Hystrix, in contrast, the spines develop into hollow quills that reach 20 cm in length. Each quill is conspicuously marked with black and white bands. These quills are densely arrayed over the rump and back. They rattle when shaken, serving as a warning to potential predators. If that doesn't work, the porcupine may attempt to charge backwards into the predator. As is the case with North American porcupines, the quills are loosely attached but can't be thrown or otherwise projected. They penetrate flesh readily, becoming stuck and detaching from the porcupine. Elsewhere on their bodies, hystricids have coarse, flat bristles. In some, these form an erectable crest on their necks and the tops of their head.
Hystricids have long skulls that are in some species inflated with air chambers over the rostrum and top of the head. They are hystricomorphous, with a huge infraorbital foramen. No accessory groove or foramen is present for nerves passing to the rostrum. The zygomatic arches are robust, but the jugal does not reach the lacrimal. Auditory bullae are small and paroccipital processes are short. The lower jaws are hystricognathous.
The dental formula of hystricids is 1/1, 0/0, 1/1, 3/3 = 20. The molars of hystricids are flat-crowned and vary from brachydont to hypsodont. The occlusal surfaces of the upper molars have three labial folds and one lingual fold; the folds are reversed on the lower molars. Toothwear causes the folds to appear as islands on the surface of the teeth.
These animals are terrestrial, not climbing trees in the manner of North American porcupines. They are excellent diggers, constructing their own burrows or appropriating and modifying those of other animals. Their diets include many kinds of plant material, but also carrion. Gnawed bones often litter the ground around their dens; these may be chewed for their calcium.
Fossil hystricids are known from the Miocene.
Families of Order Rodentia Suborder Sciurognathi Family Aplodontidae (mountain beaver, sewellel) Family Sciuridae (squirrels) Family Castoridae (beavers) Family Geomyidae (pocket gophers) Family Heteromyidae (kangaroo rats, pocket mice, and allies) Family Dipodidae (birch mice, jumping mice, jerboas) Family Muridae (familiar rates and other rodents) Family Anomaluridae (scaly-tailed squirrels) Family Pedetidae (spring hare, springhaas) Family Ctenodactylidae (gundis) Family Myoxidae (dormice and hazel mice) Suborder Hystricognathi Family Bathyergidae (mole rats, blesmols, and rats) Family Hystricidae (Old World porcupines) Family Petromuridae (rock rat or dassie rat) Family Thryonomyidae (cane rats or grasscutters) Family Erethizontidae (New World porcupines) Family Chinchillidae (Chinchillas and viscachas) Family Dinomyidae (pacarana, branick rats, false paca) Family Caviidae (cavies and guinea pigs) Family Hydrochaeridae (capybara) Family Dasyproctidae (agoutis, acouchis) Family Agoutidae (pacas) Family Ctenomyidae (tuco-tucos) Family Octodontidae (degus, coruros, rock rats) Family Abrocomidae (chinchilla rats, chinchillones) Family Echimyidae (spiny rats) Family Capromyidae (hutias, zagouties, cavies, Indian coneys) Family Heptaxodontidae (Quemi, giant hutias) Family Myocastoridae (nutria, coypu)
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