Large rodent. Variable but upper parts generally dark reddish brown speckled with black. Fur short and dense. Flanks are paler brown to yellowish extending onto the limbs. Underside and inner legs whitish, pale yellow to dark yellow. Chin and throat pale. Limbs powerfully built, digits with blackish claws. Feet buffish yellow above. Hind feet haired except for naked soles. Muzzle distinct. Ears small, rounded, and pigmented, with dense whitish to yellowish hair. White patch behind ear present but not conspicuous. No white patch above eye. Tail rather short and stout, well covered with short hairs and with a conspicuous black tip.

Psammomys obesus, the fat sand rat, is found in North Africa, ranging from Mauritania to Egypt and Sudan, and east across the Arabian Peninsula.

Biogeographic Regions: palearctic (Native )

102 records. Latest in 2000 (Kafr El-Sheikh and North Sinai).

Narrow (northern Western and Eastern Deserts, North Sinai). AOO=310.8 km². EOO=80173.7 km². 5 locations

Narrow (Morocco to Syria and parts of Arabia, south to Sudan).

The head and body length of P. obesus is 130 to 185mm, while the tail length is 110 to 150mm. Males weigh between 125 and 208g and females weigh between 146 and 207g. Psammomys obesus are heavily built, rat-like gerbils with fully haired and tufted tails. The tuft of hair on the end of the tail measures about 14mm. They have large, black eyes, robust limbs, and heavy feet with black 4 to 5mm claws. The skin is also black, most likely to protect them from the sun’s ultraviolet rays. The features used distinguish P. obesus are their nongrooved incisors and their very short, round ears.

Dorsal fur varies from light-brown to red to yellow and is speckled with black. The underbelly is a grayish/white, with the area under the chin slightly whiter than the rest of the ventral surface. The last third of the tail is black, including the tuft, while the underside is whitish.

Sexual dimorphism has not been noted in P. obesus.

Range mass: 125 to 208 g.

Range length: 130 to 185 mm.

Other Physical Features: endothermic ; homoiothermic; bilateral symmetry

Sexual Dimorphism: sexes alike

Length 144–199 mm, tail 100–157 mm, weight 92–123 gm.

Type specimen from Alexandria.

• Terrestrial

Fat sand rats are terrestrial mammals that are most often found in sandy deserts, but can be found in rocky terrain, saline-marsh areas, and loess plains. They live in burrows composed of large mouthed holes which are located near and under the bushes where they forage.

Habitat Regions: temperate ; terrestrial

Terrestrial Biomes: desert or dune

Wetlands: marsh

Inhibits salt pans and salt marshes, sandy desert and wadi beds, and occasionally gravel pans. Found along roadsides and railway embankments. Distribution dependent on the availability of succu­lent plants on which it feeds and depends for moisture.

Fat sand rats feed on the leaves of succulent plants, particularly salt bushes of the Chenopodiaceae family. Because these plants contain mostly water and salt, large amounts of leaves must be ingested in order to get enough nutrients. They can survive eating the salty plants without an abundance of water because they have extremely efficient kidneys that can excrete highly concentrated urine (about 18 times as concentrated as humans). Fat sand rats have also been known to eat grains such as barley.

Plant Foods: leaves; wood, bark, or stems; seeds, grains, and nuts

Foraging Behavior: stores or caches food

Primary Diet: herbivore (Folivore )

Because fat sand rats live under and eat the leaves of Chenopodiaceae species, they may have an impact on the populations of these bushes. However, this has not been documented. Fat sand rats are an important prey base for small to medium-sized predators in the ecosystems in which they live.

Fat sand rats are preyed upon by many small predators, such as snakes, including those in the genus Spalerosophis, owls, other birds of prey, and jackals (Canis aureus). They escape predation through their vigilance, taking refuge in burrows, and through their cryptic coloration.

Known Predators:

• diadem snakes (Spalerosophis)
• raptors (Falconiformes)
• owls (Strigiformes)
• golden jackals (Canis aureus)

Anti-predator Adaptations: cryptic

Psammomys obesus communicate with each other using high-pitched squeaks and foot drumming. It is unknown what kinds of communications these are, though the sounds may be used to warn against predators. Fat sand rats probably also use olfactory cues extensively to communicate home range boundaries and reproductive state.

Fat sand rats have keen senses of smell, vision, and hearing. Touch can be an important way of sensing the environment and communicating with conspecifics.

Communication Channels: visual ; tactile ; acoustic ; chemical

Perception Channels: visual ; acoustic

The fat sand rat lives in colonies in complex burrow systems, which have separate areas for nesting and the storage of food. Compared to other members of the Muridae family (the mice, rats and gerbils), the fat sand rat is rather unusual as it is diurnal and wholly herbivorous; most other species in this family are nocturnal and feed primarily on grains (granivorous). Its diet consists of leaves and stems and, unlike high-energy seeds, these foods are rather low in energy. As a result, it has to eat around 80 percent of its body weight in food each day to obtain sufficient energy. The fat sand rat does not need to drink water, a useful adaptation in arid habitats, and instead can get all the water it needs by feeding on the leaves of the saltbush (Atriplex halimus), which are up to 90 percent water. However, this water has an extremely high concentration of salt, and so the fat sand rat must produce very salty, concentrated urine in order to expel the salt from its body.

Breeding may take place all year round, although a peak of breeding activity has been reported between September and May. The female gives birth to a litter containing two to ten pups after a gestation period of 23 to 25 days. This species reportedly has a lifespan of around three years.

The lifespan of P. obesus in the wild is about 14 months while those in captivity can live between three and four years.

Average lifespan

Status: wild: 14 months.

Average lifespan

Status: captivity: 3-4 years.

Average lifespan

Status: captivity: 3.2 years.

Little information on the mating systems of P. obesus is available. However, the fact that dominant male home ranges are large, encompassing home ranges of several females, suggests that these males will mate with the multiple females within their home range.

Mating System: polygynous

In the wild, P. obesus is born between December and April. In captivity they can breed year round. The breeding season is dependent on the availability of food and, therefore, on the amount of rainfall. In times of drought or little rainfall, breeding has been known to stop almost completely. Gestation lasts 24 days. Litter size of ranges from 1 to 7 young. The young are born hairless, opening their eyes after one week, with weaning occurring after three weeks. Young are independent upon weaning. Females can conceive after 3 to 3.5 months of age while sexual maturity for males is reached at 4 months. Because of their short lifespan in the wild, P. obesus individuals only breed for one season, however they can give birth 2 to 4 times per season.

Breeding interval: Fat sand rats can breed 2 to 4 times per season.

Breeding season: Fat sand rats breed between December and April.

Range number of offspring: 1 to 7.

Range gestation period: 24 to 36 days.

Average weaning age: 3 weeks.

Average time to independence: 3 weeks.

Average age at sexual or reproductive maturity (female): 3 months.

Average age at sexual or reproductive maturity (male): 4 months.

Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); viviparous ; post-partum estrous

Average birth mass: 6.25 g.

Average number of offspring: 3.5.

Average age at sexual or reproductive maturity (female)

Sex: female: 100 days.

Only female fat sand rats take care of the young. Young are nursed and cared for by their mother in her den until soon before they are weaned and become independent.

Parental Investment: no parental involvement; altricial ; female parental care ; pre-fertilization (Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Female, Protecting: Female); pre-independence (Provisioning: Female, Protecting: Female)

Psammomy obesus does not appear to be a threatened or endangered species.

US Federal List: no special status

CITES: no special status

IUCN Red List of Threatened Species: least concern

Native, resident.

Least Concern. 

Uncommon; some claim populations stable (Aulagnier & Granjon 2008), while others claim they are well  known for being unstable (Ashford 2007).

Fat sand rats are known to be carriers of the parasitic disease Leishmaniasis. This disease can be transferred to humans from P. obesus by the sand fly Phlebotomus.

Negative Impacts: injures humans (causes disease in humans )

Psammomys obesus can easily acquire non insulin dependent diabetes mellitus and the complications associated with diabetes (cataracts, pancreatic atrophy, and impaired renal function) from high caloric foods such as laboratory rodent pellets. For this reason, fat sand rats are used as a model species to study diabetic mellitus and its complications.

Positive Impacts: research and education