Petromyscines are small nesomyid rodents. The head and body length ranges from 70 to 112 mm, the tail length ranges from 80 to 100 mm, and the body weight is about 20 grams. The length of the tail is less than or equal to the length of the body. Petromyscines have chunky bodies with long ears, small heads, short limbs, short, broad, hind feet, and short digits. Four of the digits on the front feet bear claws; the fifth is a stubby thumb. The hind feet have claws on all five digits. The fur on the back is golden or grayish brown, the underparts are whitish gray, and the feet are white to buffy in color. The coat is silky, soft, and straight. The tail is covered in thin hairs, and the soles of the feet lack fur except near the bases.
The petromyscine dental formula is 1/1, 0/0, 0/0, 3/3 = 16. The upper incisors are opisthodont and the upper molars lie in parallel rows. The brachydont molars have three roots in the upper jaw and two roots in the lower jaw. The second molars are smaller than the first molars, and the third molars are smaller still. The molar surface is marked by a series of alternating cusps, and the anterior laminae of the first upper molars are large and somewhat bicuspid. The hypocone and metacone of the first and second upper molars are joined together to make one large C-shaped crest. There is a labial cusp on the cingulum of the first and second molars of the lower jaw, and there is no posterior cingulum of the molars of the upper jaw. The small mandible has thin coronoid processes. The rostrum is long and slender, while the skull is wide and flat. The area between the orbits is narrow to moderately wide and has smooth edges. There are no temporal ridges. The zygomatic arches are narrow and delicate, and the infraorbital foramina are relatively large. The zygomatic plates are broad and extend anterior to the dorsal zygomatic roots. The incisive foramina are long, narrow, and reach past the first upper molars. The wide bony palate forms a shelf where it extends beyond the posterior borders of the molar rows. The mesopterygoid fossa is rectangular and narrow, and the pterygoid fossae are long, wide, and almost flat. There are large sphenopalatine vacuities. The middle lacerate foramina are small, and the lateral surface of the alisphenoid canal is formed from a strut of the alisphenoid bone. Petromyscus has an accessory foramen ovale. There is a large stapedial foramen, and the stapedial artery passes through the middle lacerate foramen as the internal maxillary artery. The auditory bullae are relatively inflated, and there is a large vacuity in the lateral surface of each mastoid bulla. (Carleton and Musser, 1984; Nowak, 1999)
The mating system of petromyscines has not been reported.
Petromyscines are seasonal breeders; their reproduction peaks in the summer (January) before heavy rainfalls arrive. Females bear one litter per year, and give birth to two or three young per litter. The young are born naked and begin growing hair one to four days after birth. The hair grows on the dorsal surface first, and then on the belly four to six days later. By the time they are 10 to 14 days old, the young are covered with dark gray fur and they are able to run quickly, climb, dig, and hop. The young stay with their mother and nurse for at least another 15 days. (Carleton and Musser, 1984; Dempster and Perrin, 1989; Nowak, 1999)
Female rock mice build nests in which they raise their young. Immediately after birth, each neonate latches on to one of its mother's nipples and clings there, presumably even when the mother goes foraging. This nipple clinging behavior is thought to be an adaptation for predator avoidance by rodents that nest in the open, rather than in burrows: the mother can quickly escape, dragging her entire litter with her. However, captive females in one study stayed in their nests when disturbed, and assumed a threatening posture, chattering their teeth (Dempster and Perrin 1989). When the young become detached from the mother's nipples, she carries them in her mouth, and retrieves any that wander away until the young are about 21 days old. Female rock mice also groom their young, and may even give them water: several young in the Dempster and Perrin (1989) study were observed licking the corners of their mother's mouth when their water bottle had become blocked. Young petromyscines stay with their mother for more than 30 days, when they are fully weaned. (Dempster and Perrin, 1989)
No information is available on the lifespan of petromyscines, but it is likely that their average lifespan is under 2 years.
Little is known about these rodents. They are nocturnal and they rest in rock crevices during the day. Petromyscines are also solitary, a trait that is evident from birth: young in the nest have no interaction with each other whatsoever, whereas young of social or colonial rodents--such as gerbils--can be observed grooming one another, chasing each other, and play-fighting. (Dempster and Perrin, 1989; Nowak, 1999)
Both young and adult rock mice squeak loudly when they are disturbed, and rock mice that are less than 35 days old also produce a rhythmic clicking sound. Although the function of these sounds is unknown, it is possible that they are a form of communication. Rock mice perceive their environment through vision, touch, smell, and hearing, although little is known about the acuity of their perception in any of these modes. (Dempster and Perrin, 1989)
There have been no reported instances of predation on petromyscines. However, it has been shown that rock mice preferentially forage near cover such as rock crevices and overhanging vegetation, where they can stay hidden from predators. Because of their size and habits, it is likely that rock mice are preyed on by raptors, snakes, and small to medium-sized mammalian carnivores. (Brown, et al., 1998)
Given a granivorous and insectivorous diet, it can be said that rock mice are primary and secondary consumers, and they are undoubtedly consumed by animals at higher trophic levels.
There are no known positive impacts of petromyscines on humans.
There are no known negative impacts of petromyscines on humans.
Petromyscus is currently not included in the IUCN's Red List of Threatened Species. However, accurate information on the natural history and status of Petromyscus species is clearly lacking. (IUCN, 2004)
Tanya Dewey (editor), Animal Diversity Web.
Allison Poor (author), University of Michigan-Ann Arbor.
living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.
uses sound to communicate
young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.
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.
an animal that mainly eats meat
uses smells or other chemicals to communicate
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.
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.
an animal that mainly eats seeds
An animal that eats mainly plants or parts of plants.
An animal that eats mainly insects or spiders.
offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).
having the capacity to move from one place to another.
This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.
the area in which the animal is naturally found, the region in which it is endemic.
active during the night
an animal that mainly eats all kinds of things, including plants and animals
breeding is confined to a particular season
remains in the same area
reproduction that includes combining the genetic contribution of two individuals, a male and a female
uses touch to communicate
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).
Living on the ground.
uses sight to communicate
reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.
Brown, J., B. Kotler, M. Knight. 1998. Patch use in the pygmy rock mouse (Petromyscus collinus). Mammalia, 62(1): 108-112.
Carleton, M., G. Musser. 1984. Muroid rodents. Pp. 289-379 in S Anderson, J Jones Jr., eds. Orders and Families of Recent Mammals of the World. New York: John Wiley and Sons.
Dempster, E., M. Perrin. 1989. Maternal behavior and neonatal development in three species of Namib Desert rodents. Journal of Zoology, 218 (3): 407-420.
Ellerman, J. 1941. The Families and Genera of Living Rodents, vol. II. London: British Museum (Natural History).
IUCN, 2004. "2004 IUCN Red List of Threatened Species" (On-line). Accessed June 07, 2005 at www.redlist.org.
Jansa, S., M. Weksler. 2004. Phylogeny of muroid rodents: relationships within and among major lineages as determined by IRBP gene sequences. Molecular Phylogenetics and Evolution, 31: 256-276.
Musser, G., M. Carleton. 1993. Family Muridae. Pp. 501-753 in D Wilson, D Reeder, eds. Mammal Species of the World. Washington, D.C.: Smithsonian Institution Press.
Musser, G., M. Carleton. 2005. Superfamily Muroidea. D Wilson, D Reeder, eds. Mammal Species of the World. Washington, D.C.: Smithsonian Institution Press.
Nowak, R. 1999. Walker's Mammals of the World, vol. 2. Baltimore and London: The Johns Hopkins University Press.
Petter, F. 1967. Particularities dentaires des Petromyscinae Roberts 1951 (Rongeurs, Cricetides). Mammalia, 31: 217-224.
Roberts, A. 1951. The mammals of South Africa. South Africa: Central News Agency.
Simpson, G. 1945. The principles of classification and a classification of mammals. Bulletin of the American Museum of Natural History, 85: 1-350.
Steppan, S., R. Adkins, J. Anderson. 2004. Phylogeny and divergence-date estimates of rapid radiations in Muroid rodents based on multiple nuclear genes. Systematic Biology, 53(4): 533-553.