Six species in 3 genera make up this family, which is found along the central and southern Andes and throughout most of Patagonia in southern South America.
Members of this family are medium (500 gms) to large-sized rodents (8kg) with thick, soft fur; well-developed hind limbs, which are longer than the forelimbs; large eyes; and moderately large ears. Their tails are bushy and range from short up to about 1/3 the length of the body; in the species with the longest tail (Lagostomus), however, the tail is easily broken and often partly lost. Fleshy pads called pallipes are found on the feet of all chinchillids. The soles are not furry. The forefeet have four toes, which are easily manueverable and used for grasping. The number of toes on the hind feet is reduced to 4 in Lagidium and Chinchilla (both of which have weakly developed hind claws) and 3 in Lagostomus (strong hind claws), which are powerful diggers. Plains viscachas (Lagostomus) have a striking black and white facial pattern, lacking in the other species; the bodies of all are grey or grey-brown dorsally and paler on the venters.
The crania of chinchillids are hystricognathous, but the condition is not as strongly developed in this group as in most of the South American Hystricognathi, probably due to secondary loss. They are, however, strongly hystricomorphous, with a much-enlarged infraorbital foramen and reduced zygomatic plate. The mandibles have no masseteric crest. Lacrimals are large, and the lacrimal canal opens on the side of the rostrum. The auditory bullae range from moderately large to extremely inflated (chinchillas), and the paroccipital processes can be either long or short. The cheek teeth of chinchillids (dental formula 1/1, 0/0, 1/1, 3/3 = 20) are hypsodont and evergrowing (rootless). Their occlusal surfaces are composed of 2 or 3 closely packed lamellar plates. All chinchillids have fairly delicate incisors.
Members of this family often jump bipedally, but mostly they move on all four limbs. Chinchillas and mountain viscachas (Lagidium) live in mountainous, rocky areas, where they move over and through the rocks with great agility. They are not strong diggers. Plains viscachas live in the great plains areas of Argentina, from the Chaco in the north to Patagonia in the south. They are excellent diggers and construct extensive burrow systems. This habit that has not endeared them to ranchers, whose livestock sometimes break legs when they step into viscacha holes.
Chinchillas, mountain viscachas, and plains viscachas are all colonial, living in groups that range from a few individuals to hundreds. Mountain and especially plains viscachas have fairly large repertoires of vocalizations used in social interactions. Unfortunately, chinchillas are nearly extinct in the wild, so little is known of their behavior under natural conditions. Viscachas, once abundant, are now seriously threatened and uncommon. Mountain viscachas are uncommon and live in remote areas. As a result, none of the species in this family have been thoroughly studied under natural conditions. All are primarily vegetarian. It is said that 10 plains viscachas eat as much as one sheep, another aspect of their biology that has earned them the wrath of agriculturalists.
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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