Petromus typicusdassie rat

Last updated:

Geographic Range

The rock rat or dassie rat is found in western South Africa, Namibia and southwestern Angola. (Heinemann, 1975)

Habitat

Petromus typicus are generally found in crevices and rocky cavities of stony deserts. They live in the rocky areas of hills and mountains, where they rest and sun on warm rocks beneath overhangs for protection from flying predators. Mean annual rainfall in areas where Petromus typicus live is usually greater than 25 mm, and their habitat boundaries are often limited by areas of moist woodlands or cold, wet winters. Rock rats seek food on the ground or in low bushes. (Coetzee, 2002; Heinemann, 1975; Nowak, 1997)

Physical Description

Rock rats are small mammals, ranging in size from 100 to 300 grams. They have flat skulls with short ears, long black facial whiskers, yellowish noses, and hypsodont cheekteeth. Their teeth include narrow incisors and total 20 in number, in the pattern 1:1; 0:0; 1:1; 3:3. Their feet and claws are narrow, the forepaws have 4 digits and the hindpaws have 5 digits. Rock dassies' fur grows in clusters of 3-5 hairs, creating a bristly appearance, but it is generally smooth and soft to the touch. Their bodies blend in with the rocks, the dorsal side having a greyish tawny color and the ventral side grey or yellow. They also have incredibly flexible axial skeletons, allowing them to slip through narrow rock cracks for protection and shelter. With their short legs and squat build, these mammals are more adapted to running rather than jumping and locomote by running over the rocks of their habitat. Testes in the males are semi-internal and generally inconspicuous. The nipples of female rock rats are lateral and high on level with the scapula, allowing young to nurse from the sides when hiding in crevices. (Heinemann, 1975; Nowak, 1997; Shortridge, 1934)

  • Sexual Dimorphism
  • sexes alike
  • Range mass
    100 to 300 g
    3.52 to 10.57 oz
  • Range length
    27 to 38 cm
    10.63 to 14.96 in

Reproduction

Relatively little is known regarding the mating systems of Petromus typicus.

Mating takes place in early summer, during the months of November and December. This breeding season appears to be fixed, and may be related either to the onset of the rainy season or it may be endogenous to the animals. (Coetzee, 2002; Coetzee, 2002; Heinemann, 1975; Nowak, 1997; Shortridge, 1934)

Females give birth to 1-3 young in late December or early January after a gestation period of about three months, and the young are precocial, rather large, and covered with hair. Young rock rats begin to eat solid food at around 14 days, weaning about one week later. Petromus typicus reach adulthood near the age of nine months. (Coetzee, 2002; Heinemann, 1975; Coetzee, 2002; Heinemann, 1975)

  • Breeding interval
    Rock rats breed once yearly, in the summer months.
  • Breeding season
    Mating occurs in November or December.
  • Range number of offspring
    1 to 3
  • Average number of offspring
    1.9
    AnAge
  • Average gestation period
    3 months
  • Average weaning age
    21 days
  • Average time to independence
    9 months

Little is known regarding the parental investment of Petromus typicus.

Lifespan/Longevity

The lifespan of Petromus typicus is unknown.

Behavior

Dassie rats living in rocky areas usually emerge from their small crevices in the morning and late afternoon to forage and bask in the sun. Occasionally they also seek food after sunset, especially when there is a bright moon. They move across their rocky habitats by running and often jumping, spreading out and flattening their bodies in the manner of flying squirrels. Seeking food on the ground or in bushes, they travel alone or in pairs. Researchers who have been able to observe rock rats find that they are a playful species and sometimes frolick among plant stems. When disturbed they quickly dart into the safety of thin crevices and issue a warning call to other members of the species. (Heinemann, 1975; Nowak, 1997)

Home Range

In one study, 15 individuals were recorded in a 6 hectacre area. Rock hyraxes, Procavia capensis, another small herbivorous mammal, compete with rock rats for shelter. In areas where these two species overlap, Petromus typicus are restricted to smaller crevices where Procavia capensis cannot fit. (George and Crowther, 1981; George and Crowther, 1981; Nowak, 1997)

Communication and Perception

Little is known about communication among Petromus typicus, although they have been observed to emit a single whistling note as a warning signal to other rock rats when a predator is sighted. (Nowak, 1997)

Food Habits

Petromus typicus are herbivores. They feed on the blossoms of certain desert and steppe plants, as well as on greens, seeds, berries and fruits that they seek on the ground or in bushes. (Heinemann, 1975; Nowak, 1997)

  • Plant Foods
  • leaves
  • seeds, grains, and nuts
  • fruit
  • flowers

Predation

Known predators of dassie rats include numerous birds of prey, although particular species are not mentioned in current literature. To avoid aerial predators, rock rats often forage beneath rocky overhangs, out of view from birds above them. They are also protectively colored, blending in well with their rocky surroundings. (Heinemann, 1975; Nowak, 1997; Shortridge, 1934)

  • Anti-predator Adaptations
  • cryptic
  • Known Predators

Ecosystem Roles

As mentioned, Petromus typicus are prey for aerial predators. They are also seed predators, and possibly seed dispersers. (Shortridge, 1934)

Two parasites of Petromus typicus are mentioned in current literature, Acanthoxyurus shortridgei monnig and Heteroxynema cafer. Both parasites are nematodes. The specific physiological effects of these parasites on rock rats are unknown. (Hugot, 1983)

  • Ecosystem Impact
  • disperses seeds
Commensal/Parasitic Species
  • Acanthoxyurus shortridgei monnig
  • Heteroxynema cafer

Economic Importance for Humans: Positive

The economic importance of Petromus typicus is unknown.

Economic Importance for Humans: Negative

The economic importance of Petromus typicus is unknown.

Conservation Status

Rock dassies are not currently considered endangered, threatened or vulnerable.

Contributors

Matthew Wund (editor), University of Michigan-Ann Arbor.

Kari Santoro (author), University of Michigan-Ann Arbor, Phil Myers (editor, instructor), Museum of Zoology, University of Michigan-Ann Arbor.

Glossary

Ethiopian

living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.

World Map

acoustic

uses sound to communicate

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

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

desert or dunes

in deserts low (less than 30 cm per year) and unpredictable rainfall results in landscapes dominated by plants and animals adapted to aridity. Vegetation is typically sparse, though spectacular blooms may occur following rain. Deserts can be cold or warm and daily temperates typically fluctuate. In dune areas vegetation is also sparse and conditions are dry. This is because sand does not hold water well so little is available to plants. In dunes near seas and oceans this is compounded by the influence of salt in the air and soil. Salt limits the ability of plants to take up water through their roots.

diurnal
  1. active during the day, 2. lasting for one day.
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.

folivore

an animal that mainly eats leaves.

herbivore

An animal that eats mainly plants or parts of plants.

motile

having the capacity to move from one place to another.

mountains

This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.

native range

the area in which the animal is naturally found, the region in which it is endemic.

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

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

solitary

lives alone

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

visual

uses sight to communicate

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

References

Coetzee, C. 2002. The distribution and breeding seasons of the dassie-rat, Petromus typicus. Folia Zoologica, 51 (Supplement 1): 23-25.

George, W., G. Crowther. 1981. Space partitioning between two small mammals in a rocky desert. Biological Journal of the Linnean Society, 15 (3): 195-200.

Heinemann, D. 1975. Old World Porcupines, Mole Rats, Rock Rats and African Cane Rats. Pp. 419-426 in B Grzimek, ed. Grzimek's Animal Life Encyclopedia, Vol. 11, 2 Edition. New York: Van Nostrand Reinhold Company.

Hugot, J. 1983. 2 Oxyurid parasites of Petromus typicus, an archaic South African rodent. Bulletin du Museum National D'Histoire Naturelle Section a Zoologie Biologie et Ecologie Animales, 5(1): 187-200.

Nowak, R. 1997. "Petromus typicus" (On-line). Walker's Mammals of the World. Accessed March 08, 2004 at http://www.press.jhu.edu/books/walkers_mammals_of_the_world/rodentia/rodentia.petromuridae.petromus.html.

Shortridge, G. 1934. The Mammals of Southwestern Africa. London: William Heinemann Ltd..

Wilson, D., D. Reeder. 1993. Mammal Species of the World: A Taxonomic and Geographic Reference. Washington and London: Smithsonian Institution Press.