Heteromyidaekangaroo rats, pocket mice, and relatives

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There are approximately 59 members of this family, allocated to 6 genera. They are found in western North America, throughout Mexico and Central America, and in northwestern South America.

Heteromyids are small to medium-sized rodents. Many species live in the deserts and dry grasslands of the western United States and Canada. These include kangaroo rats and mice, which are strikingly modified for jumping with long, powerful hind limbs; a long and tufted tail; relatively short front limbs; and compressed, partly fused neck vertebrae. The hind limbs are lengthened mostly by an increase in length of the metatarsals and digits, and these feet are further specialized by the near loss of the first digit. They move primarily by hopping on their hind limbs. These heteromyids also have enormously enlarged bullae. Pocket mice are smaller, and while they are saltatorial, their hind limbs are not as modified as those of kangaroo rats and their locomotion is primarily quadrupedal. Members of the genera Heteromys and Liomys are even less modified; their locomotion is quadrupedal. They are found in both wet and dry tropical forests in Mexico south to northern South America.

All heteromyids have a large, furlined cheek pouch that opens next to the mouth and extends back along the shoulders. Their skulls vary considerably, but all are thin and papery and lack well developed ridges and crests (very unlike the robust skulls of related geomyids). The nasals are narrow and the zygomatic arches thin. The opening of the infraorbital canal is sunk into a vacuity that penetrates the rostrum. Heteromyids are sciuromorphous and sciurognathus, and they have a well developed zygomatic plate and a small infraorbital foramen. Their dental formula is 1/1, 0/0, 1/1, 3/3 = 20, and their cheek teeth are hyposodont (but not evergrowing except in kangaroo rats). The molars have a distinctive 2-lobed pattern in most species.

The pelage of heteromyids varies in texture from silky and soft to spiny. Its color varies considerably among species and geographically within species, often matching the color of the soil on which the animals live.

Heteromyids feed on seeds and other plant parts, but they sometimes also include some animal matter. They gather seeds in their cheek pouches and store them in their burrows for later consumption. Most species burrow, forming complex tunnel systems with multiple chambers and openings to the surface. Kangaroo rats have a remarkable ability to live without access to free water.

Heteromyids are first known from the Oligocene. Kangaroo rats were first seen in the Pliocene, at a time when the drylands occupied by the majority of modern species were widespread in North America.

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.

McLaughlin, C. A. 1984. Protrogomorph, sciuromorph, castorimorph, myomorph (geomyoid, anomaluroid, pedetoid, and ctenodactyloid) rodents. Pp. 267-288 in Anderson, S. and J. K. Jones, Jr. (eds). Orders and Families of Recent Mammals of the World. John Wiley and Sons, N.Y. xii+686 pp.

Paradiso, J. L. 1975. Walker's Mammals of the World, Third Edition. Johns Hopkins University Press, Baltimore.

Savage, R. J. G. and M. R. Long. 1986. Mammal Evolution, an Illustrated Guide. Facts of File Publications, New York. 259 pp.

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, D. E., and D. M. Reeder. 1993. Mammal Species of the World, A Taxonomic and Geographic Reference. 2nd edition. Smithsonian Institution Press, Washington. xviii+1206 pp.

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