By Phil Myers
This family consists of 1 genus and 1 species found in southwestern Africa.
Dassie rats are squirrel-like, with a long and hairy (but not or only slightly bushy) tails, body 150-200 mm in length, blunt heads, short rounded ears, and large eyes. The limbs are only moderately long, and the feet are narrow, with four main digits and short claws. Bristle-like hairs associated with claws of the hind feet form a sort of comb, probably used in grooming. The fur of a dassie rat is soft and silky, but there is no underfur. Pelage color varies considerably, but is usually some shade of brown, gray, or buff.
The 
skulls of dassie rats are hystricomorphous, with a greatly enlarged infraorbital canal and an accessory canal or groove that transmits nerves to the rostrum. They are broad and flat in profile, but ridges and crests for the attachment of muscles are not well developed. Auditory bullae are large, and the paroccipital processes are long and curved around the bullae. The zygomatic arches are strongly built, but the jugal does not contact the lacrimal. The palate is long, extending well beyond the toothrow. The lower jaws are hystricognathous but not strongly so; the angular process is only slightly deflected.
The dental formula of petromurids is 1/1, 0/0, 1/1, 3/3 = 20. The incisors are narrow. Cheekteeth are hypsodont but only on one side, resulting in a terraced appearance. Both upper and lower molars have one labial and one lingual fold. The cheekteeth are not evergrowing.
Rock rats live in groups in arid rocky areas. They are active during the day. Group members use a distinctive whistle to warn of predators. Their diet consists primarily of grass stems and leaves, with some insects also included. They do not require free water. Dassie rats squeeze into rock crevices when threatened, and one of their most remarkable characteristics is their ability to flatten their bodies. Their ribs are flexible and their skulls are unusually flat. The females even have their nipples on their sides, rather than on their undersides, so that young can nurse even when their mother is hiding flattened in a crack.
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.
Macdonald, David. 1984. The encyclopedia of mammals. Facts on File Publications, New York.
Nowak, R. M. and J. 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, D. E. and D. 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, S. and J. K. 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.
