Cardiocranius paradoxus
five-toed pygmy jerboa

Five-toed pygmy jerboas, Cardiocranius paradoxus, are found only in a few areas in Asia. In Russia they are found in the Ubsu-Nur Depression of the Tuva Autonomous Region in the extreme south-central part of the country. In Kazakhstan, their range is restricted to a small area north of Lake Balkhash, where the species was first discovered. They are also found throughout western and southern Mongolia, as well as in the Nan Shan Mountains of northern China. ("Five-toed Dwarf Jerboa", 1999; Gromov and Eszhanov, 2004; Gromov, 2002)

Five-toed pygmy jerboas are especially adapted to rocky deserts. These animals prefer to have dunes or outcroppings with ample vegetative cover within their home ranges. The protective shrubbery offers a safe place under which to burrow. ("Five-toed Dwarf Jerboa", 1999; Gromov, 2002)

Cardiocranius paradoxus generally reaches a body length of 50 to 75 mm, with the tail extending a further 70 to 78 mm. These small jerboas are grayish buff with white underbellies. The tail is thinly haired and is light brown above and white below. Although rather slim at the base, the tail quickly thickens before coming to a tapering point. At the end of the tail is a tuft of hair. ("Five-toed Dwarf Jerboa", 1999)

In most jerboas, the three metatarsals near the center of each hind foot fuse to form a cannon bone, thus there are a total of three toes on each hind foot. Instead, C. paradoxus has five individual toes. The two outside toes (digits 1 and 5) are rather small in comparison to the three central toes, but they are present nonetheless and give this species its common name. The hind foot exhibits a patch of bristly hairs on the sole, which help five-toed pygmy jerboas to obtain better traction on loose sand. ("Five-toed Dwarf Jerboa", 1999)

The skull of these small jerboas is heart-shaped, which explains the origin of the generic name, Cardiocranius. Although the external ears are extremely small, the auditory bullae are greatly inflated, allowing C. paradoxus to hear quite well and sense low frequency vibrations. Five-toed pygmy jerboas have large upper incisors that are grooved on the front surface. ("Five-toed Dwarf Jerboa", 1999)

The lifespan of Cardiocranius paradoxus is currently not known and further data are needed on the subject. A close relative, Jaculus jaculus, is known to live for up to 4 years in the wild and up to 6 years in captivity.

Five-toed pygmy jerboas are strictly nocturnal, preferring to be most active mainly from 2200 to 0400 hours (10:00pm to 4:00am). During this time, an individual will move almost non-stop around its home range. Observations show that roughly 90% of the active period is devoted to exploratory activity, while the rest of the time is used for feeding, brief periods of rest (about 2 to 5 minutes at a time), and burrowing. ("Five-toed Dwarf Jerboa", 1999; Gromov and Eszhanov, 2004; Gromov, 2002)

Five-toed pygmy jerboas move by small hops, although crawling is occasionally observed. When a jerboa moves, it never moves in a straight line, but rather changes directions constantly so as to appear to move in circles. When startled, an individual might jump as high as 20 to 30 cm straight up into the air. (Gromov and Eszhanov, 2004; Gromov, 2002)

Five-toed pygmy jerboas may dig their own burrows or utilize the abandoned burrows of other animals. When digging its own burrow, an individual uses its hind legs to rake and kick the soil. A burrow is usually dug under a bush that offers cover and the entrance is often hidden by a pile of dry grass. Burrows have been observed to be roughly 25 to 30 cm deep with a central nesting chamber about 10 to 11 cm in diameter. Burrows are used as a safe place to rest, hibernate, and rear young, although further studies should be pursued for more details on burrow use. (Gromov and Eszhanov, 2004; Gromov, 2002)

Home Range

Five-toed pygmy jerboas generally have a home range of about 14,300 squared meters. Observations have shown that individuals will move throughout the entire home range during foraging, but will spend a majority of the time in one or two areas within the range. Jerboas have a number of burrows scattered around the territory so that a safe haven is never too far off. (Gromov and Eszhanov, 2004; Gromov, 2002)

Like other jerboas, ive-toed pygmy jerboas have a keen sense of hearing, smell, and vision. The greatly inflated auditory bullae allow five-toed pygmy jerboas to sense vibrations produced by low frequency sounds, as well as aid in their sensitive hearing. As is true for most rodents, this species likely communicates largely using olfactory cues. ("Five-toed Dwarf Jerboa", 1999)

These small rodents are strictly herbivorous. The diet of Cardiocranius paradoxus mainly consists of seeds and leaves of the grasses and low-growing vegetation found in its habitat. This species is also known to eat the occasional flower. Five-toed pygmy jerboas eat only the juiciest parts of the leaves, although it has been observed that they will also nibble on dead grass. Seeds are collected from the plants themselves, as well as from the ground. (Gromov and Eszhanov, 2004; Gromov, 2002)

Predators of Cardiocranius paradoxus include common foxes (Vulpes vulpes), Corsac foxes (V. corsac), Eversmann's polecats (Mustella eversmanni), long-eared hedgehogs (Erinaceus auritus), short-eared owls (Asio flammeus), and little owls (Athene noctua). When faced with a predator, these pygmy jerboas hop rapidly (and in a zig-zag manner) for the cover of a shrub or burrow. (Gromov and Eszhanov, 2004)

The largest role that Cardiocranius paradoxus plays in the ecosystem is as prey for the animals that prey upon it. They are also important predators on seeds in the ecosystems they inhabit. (Gromov and Eszhanov, 2004)

Cardiocranius paradoxus has no known negative economic importance for humans.

Five-toed pygmy jerboas have no known positive economic importance for humans aside from their role as members of healthy, desert ecosystems.

Five-toed pygmy jerboas are widely regarded as vulnerable and rare. They are especially rare in China. The causes of the decline being observed in five-toed pygmy jerboa populations ranges from habitat destruction to predation and interspecific competition. Climatic changes in their usually dry desert habitats are causing increased moisture levels, which in turn lead to rapid plant growth. This eliminates some of the rocky desert habitat that these jerboas require. Human expansion is also degrading this limited habitat type. Increased predation is seriously decimating jerboa populations in Kazakhstan. Interspecific competition with other rodents for food and habitat is also taking its toll in the Russian populations. ("Five-toed Dwarf Jerboa", 1999; Gromov and Eszhanov, 2004; Gromov, 2002)