Chinchillidaechinchillas and viscachas

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.

References and literature cited:

Feldhamer, G. A., L. C. Drickamer, S. H. Vessey, and J. F. Merritt. 1999. Mammalogy. Adaptation, Diversity, and Ecology. WCB McGraw-Hill, Boston. xii+563pp.

Lawlor, Timothy. 1979. Handbook to the orders and families of living mammals. Mad River Press, Eureka, California.

Macdonald, David. 1984. The encyclopedia of mammals. Facts on File Publications, New York.

Nowak, Ronald M. and John L. Paradiso. 1983. Walker's mammals of the world. The Johns Hopkins University Press, Baltimore and London, pp 803-810.

Vaughan, T. A. 1986. Mammalogy. Third Edition. Saunders College Publishing, Fort Worth. vii+576 pp.

Vaughan, T. A., J. M. Ryan, N. J. Czaplewski. 2000. Mammalogy. Fourth Edition. Saunders College Publishing, Philadelphia. vii+565pp.

Wilson, Don E. and DeeAnn M. Reeder (eds.). 1993. Mammal species of the world: A taxonomic and geographic reference, 2nd ed.. Smithsonian Institution Press, Washington and London.

Woods, C. A. 1984. Hystricognath rodents. Pp. 389-446 in Anderson, Sydney and J. Know Jones, Jr. (eds.). Orders and familes of mammals of the world. John Wiley and Sons, New York.

Contributors

Phil Myers (author), Museum of Zoology, University of Michigan-Ann Arbor.

Glossary

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

chemical

uses smells or other chemicals to communicate

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

motile

having the capacity to move from one place to another.

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

tactile

uses touch to communicate