Geographic Range
The rock rat or dassie rat is found in western South Africa, Namibia and southwestern
Angola.
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.
- Habitat Regions
- temperate
- terrestrial
- Terrestrial Biomes
- desert or dune
- mountains
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.
- Other Physical Features
- endothermic
- homoiothermic
- bilateral symmetry
- Sexual Dimorphism
- sexes alike
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.
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.
- Key Reproductive Features
- seasonal breeding
- gonochoric/gonochoristic/dioecious (sexes separate)
- sexual
- viviparous
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.
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.
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.
- Communication Channels
- acoustic
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.
- 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.
- Anti-predator Adaptations
- cryptic
Ecosystem Roles
As mentioned,
Petromus typicus
are prey for aerial predators. They are also seed predators, and possibly seed dispersers.
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.
- Ecosystem Impact
- disperses seeds
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.
Additional Links
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.
- Ethiopian
-
living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- 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.
- 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.
- mountains
-
This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.
- 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.
- 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.
- seasonal breeding
-
breeding is confined to a particular season
- sexual
-
reproduction that includes combining the genetic contribution of two individuals, a male and a female
- viviparous
-
reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.
- diurnal
-
- active during the day, 2. lasting for one day.
- motile
-
having the capacity to move from one place to another.
- sedentary
-
remains in the same area
- solitary
-
lives alone
- acoustic
-
uses sound to communicate
- visual
-
uses sight to communicate
- tactile
-
uses touch to communicate
- 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.
- herbivore
-
An animal that eats mainly plants or parts of plants.
- folivore
-
an animal that mainly eats leaves.
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 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.