Physical characteristics

Mole-rats show anatomical adaptations for life underground. Their limbs are short, their bodies are cylindrical in shape, their necks muscular, but indistinct from the head and

The Queen the breeding female

The Queen the breeding female

The Harem

1-3 males the queen has chosen to mate with

The Soldiers both males and females who defend against predators and foreign mole-rats

The Harem

1-3 males the queen has chosen to mate with

The Soldiers both males and females who defend against predators and foreign mole-rats

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The Workers those responsible for gathering food, excavating burrows, and caring for the queen and her pups

Mole-rats social structure. (Illustration by Katie Nealis)

body. Their heads are robust, ending in flattened pig-like noses. Their streamlined shape and short limbs enable them to move backwards and forwards with equal ease in the narrow confines of their burrows. The outer edges of their hind

A Cape mole-rat (Georychus capensis), South Africa. (Photo by © Michael Dick/Animals Animals. Reproduced by permission.)

feet are fringed with stiff hairs and these, together with a brush of stiff hairs on their short tails (in all except in the naked mole-rat), help hold soil when they move it along the burrows. Their eyes are small and, at best, can only detect light and dark. Their ears lack external pinnae, and their range of hearing is more restricted than that of aboveground rodents. Nevertheless, at least two species of social mole-rats (Hetero-cephalus and Cryptomys mechowi) have large vocal repertoires, indicating relatively sophisticated levels of communication.

Their hair (except in the naked mole-rat) tends to be thick, short, and easily reversible; this is an asset when moving to and fro in the burrow. Strong muscles lying under a very loose skin enable them to vigorously shake their fur free of adhering soil. The loose skin also facilitates turning round in the narrow confines of the burrow. Because mole-rats live in dark burrows, the sense of touch is important to them. Stiff, tactile hairs scattered over much of the body, and projecting above the level of the rest of the hair, act in much the same way as the whiskers of a cat. Long, stiff sensory hairs abound on the front of the face and are also clustered above the eyes. Although otherwise lacking a coat of hair, all these sensory hairs are present in naked mole-rats.

A notable feature of mole-rats is a pair of large, evergrowing, and forwardly-directed incisors; these lie outside the mouth (extra-buccal). All mole-rats, except Bathyergus, are chisel-tooth diggers, that is, they excavate their burrows by biting at the soil with their incisors. Strongly haired, muscular lips meet behind the incisors to keep soil out of the mouth

Dirt piles being swept backward o

Dirt piles being swept backward o

Mole-rats digging system. (Illustration by Katie Nealis)

during digging. In all genera, except Bathyergus, the roots of the upper incisors extend back to originate behind the molars. It has been shown that a disproportionate amount of the brain of naked mole-rats is devoted to picking up sensory signals from these incisors; this is probably also true for the other chisel-tooth diggers in this family. The lower jaws of chisel-tooth diggers can move independently so that their incisors can be splayed apart or brought together, thereby making them a very versatile set of tools. Mole-rats groom lower incisors against the upper ones to sharpen their tips. The skull is dorsally flattened and houses strong jaw muscles (masseter and temporal) that are used in feeding and digging.

Physiological adaptations to subterranean life include a tolerance to high carbon dioxide and low oxygen concentrations and, at least in the naked mole-rat (and possibly others), a blood hemoglobin with a high affinity for oxygen. Mole-rats, like many subterranean mammals, have lower body temperatures and resting metabolic rates than do mammals of similar size living aboveground. The humidity in burrows is high and, consequently, evaporative water loss and convective cooling are of little use if the animal overheats when digging. The naked mole-rat has the poorest thermoregulatory ability of the family; indeed, its body temperature varies with ambient temperature in a similar way to reptiles and, in the wild, it usually lies between 82.4 and 86°F (28-32°C), which is close to the burrow temperature. They regulate their body temperature by moving up and down in the burrows and by huddling together. Microorganisms in the cecum aid in the

A common mole-rat (Cryptomys hottentotus) tunnels into a dirt burrow. A common mole-rat (Cryptomys hottentotus) in South Africa. (Photo by (Photo by © Jeffrey L. Rottman/Corbis. Reproduced by permission.) Animals Animals ©D. Curl, OSF. Reproduced by permission.)
A close-up view of the incisors on a common mole-rat (Cryptomys hot-tentotus), with the lips closed behind the teeth. (Photo by © Jeffrey L. Rottman/Corbis. Reproduced by permission.)
The naked mole-rat (Heterocephalus glaber) is native to East Africa. (Photo by Scott Camazine/Photo Researchers, Inc. Reproduced by permission.)

digestion of fibers in their diet; to fully utilize these digested foods, mole-rats practice coprophagy, a process in which they double up and eat some of the energy-rich feces as they are voided.

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