Dassie rats

(Petromuridae)

Class Mammalia

Order Rodentia

Suborder Hystricognathi

Family Petromuridae

Thumbnail description
Squirrel-like, with less bushy tails and a scattered cover of long hair over the last three-quarters of the tail; pelage is soft and silky with no underfur; a yellow enamel layer on the front of the small, narrow and ungrooved incisors

Size
9.9–10.9 in (253–279 mm); 6.0–9.2 oz (170–262 g)

Number of genera, species
1 genus; 1 species

Habitat
Rocky areas in the South West Arid Zone of Africa

Conservation status
Not globally threatened

Distribution
Southern Angola, Namibia, and northwestern South Africa

Evolution and systematics

In 1939, Broom described a fossil form found at Taung (South Africa) as Petromus minor. Some 14 subspecies have been described, but Meester and co-workers (1964) feel that it is unlikely that 14 valid forms could occur in such a restricted range of the species. At present the family includes only one species, Petromus typicus. The name is derived from the Greek petro, "rock," and mys, "mouse." The species name refers to the Greek word typicos, "typical," i.e., a typical rat of the rocks.

The taxonomy for this species is Petromus typicus A. Smith, 1831, South Africa.

Physical characteristics

In external appearance this rodent is somewhat squirrel-like, although the tail is not bushy. It is shorter than the head body length and the last three quarters of it is covered with long hair, which do not fan out. They have short, blackish ears that are rather higher than broad. They have long black vibrissae. Data concerning size are meager with males: head and body length 10.9–14.0 in (27.9–36.0 cm); mass of

two sub-adults 6.0 and 7.4 oz (170 and 212 g), and females: head and body length 9.9–14.0 in (25.3–35.8 cm); mass of two adult females 8.8 and 9.2 oz (251 and 262 g). Colors are geographically variable, and normally come in shades of brown, gray, or buff, with yellowish to dirty underparts. The front feet have four clawed toes with a short and rudimentary thumb. The five toes of the hind feet have short curved claws. The soles of the feet are naked with well-developed pads for moving on rocky substrates. They have a remarkable ability to flatten their bodies, due to flexible ribs and unusually flat skulls. The dental formula is (I1/1 C0/0, P1/1, M3/3) × 2 = 20.

Distribution

They have a fairly restricted distribution in the South West Arid Zone of Africa, stretching from the southwestern parts of Angola throughout the central and western parts of Namibia to the northwestern parts of the Northern Cape Province in South Africa.

Habitat

They are confined to rocky areas where they occupy crevices or take cover under piles of boulders. They may be scattered throughout different types of vegetation and shelter seems to be more important than the available vegetation type.

Behavior

Dassie rats are diurnal and occur singly, in pairs, or in family groups. Because of the flat skull and the manner in which they can flatten the body they can squeeze into very narrow crevices when threatened. They can utilize crevices too narrow even for small hyraxes. Their rock shelters have lookout points, sunbathing platforms and are linked to suitable feeding grounds. They are a docile species with activity noticeable during early morning and late afternoons. Although they will defecate anywhere within the home range, they tend to have latrines where they urinate, causing the rocks to become whitish stained. They love to sun and dust-bathe themselves near their shelters. When threatened they run with great speed for shelter, jumping from rock to rock. They have low water requirements and probably get most of their water from the food they eat.

Feeding ecology and diet

They are vegetarian feeding on grasses, twigs, and shrubs. They will climb trees to plug leaves. Flowers of the many species of Compositae growing in their immediate vicinity are also sought after. Grass and leaves may be taken to their shelters where it is either eaten, or used for nest-building. Apparently they are unique in that they may regurgitate food back to the mouth where it is then masticated and reswallowed. They are coprophagous and sometimes eat some of their own pellets.

Reproductive biology

Data meager. Gravid females were found during the spring months (September-November) in Namibia. The number of young varies from one to two. Young are born in an advanced stage of development. Females have three pairs of teats, two laterally situated pairs below the shoulders with the third pair, often non-functional, further back.

Conservation status

In 1996 they were listed as Lower Risk/Least Concern, a the IUCN Red List. During 2002 they were globally listed as Lower Risk/Least Concern. Nationally they could be regarded as Vulnerable, but due to the small area of occupancy and the current inferred stability it is down rated to Lower Risk/Near Threatened.

Significance to humans

None known.

Resources

Books

De Graaff, G. The Rodents of Southern Africa. Durban and Pretoria: Butterworths, 1981.

Meester, J. A. J., I. L. Rautenbach, N. J. Dippenaar, and C. M. Baker. Classification of Southern African Mammals. Transvaal Museum Monograph, No. 5. Pretoria: Transvaal Museum, 1986.

Meester, J., D. H. S. Davis, and C. G. Coetzee. An Interim Classification of Southern African Mammals. Zoological Society of Southern Africa and CSIR, 1964.

Mills, M. G. L., and H. L. Hes. The Complete Book of Southern African Mammals. Cape Town: Struik Winchester, 1997.

National Research Council. Microlifestock: Little-Known SmallAnimals with a Promising Economic Future. Washington, DC: National Academic Press, 1991.

Rosevear, D. R. The Rodents of West Africa. London: British Museum (Natural History), 1969.

Skinner, J. D., and R. H. N. Smithers. The Mammals of theSouthern African Subregion. Pretoria: University of Pretoria, 1990.

Walker, E. P. Mammals of the World. 2 vols. 3rd ed. Baltimore: Johns Hopkins Press, 1975.

Wilson, D. E., and D. M. Reeder. Mammal Species of the World. Washington, DC: Smithsonian Institution Press, 1993.

Woods, C. A. "Hystricognath Rodents." In Orders and Families of Recent Mammals of the World, edited by S. Anderson and J. Knox Jones Jr. New York: John Wiley, 1984.

Periodicals

Bate, D. M. A. "An Extinct Reed-rat Thryonomys arkelli from the Sudan." Annual Magazine of Natural History 14, no. 11: 65–71.

Broom, R. "The Fossil Rodents of the Limestone Cave at Taungs." Annuals of the Transvaal Museum 19 (1999): 315–317.

Romer, A. S., and P. H. Nesbit. "An Extinct Cane-rat Thryonomys logani from the Central Sahara." Annual Magazine of Natural History 6, no. 10: 687–690.

Mac van der Merwe, PhD