Physical characteristics

The characteristics that describe members of the family Erinaceidae are generally considered primitive. They are typ ical insectivores—small animals, with short legs and large feet. Feet have five digits, except in some of the African hedgehogs (genus Atelerix) in which the hallux or big toe is reduced or vestigial. All erinaceids walk with a flat-footed "plantigrade" gait. The two bones of the lower hind leg, the tibia and fibula, are fused into one. The tail is hairy and variable in length, the muzzle is elongated—more so in the gymnures than the hedgehogs. The eyes are small, though better developed than those of most other insectivores. The skulls of hedgehogs and gymnures vary quite considerably, from long and narrow to short and broad. All have a small braincase.

As a general rule, hedgehogs are more derived than gymnures, which have retained many characteristics of their early insectivore ancestors. The most obvious difference between the two subfamilies is the coat. While the gymnures and moonrats are covered in pelage of soft fur, the hedgehogs sport a dense coat of narrow spines, starting on the head and covering the back and flanks. The color varies between and within species, but is usually some shade of yellow- or grayish brown to black.

Hedgehogs and gymnures have similar dentition. The dental formula for the family is (I2-3/3 C1/1 P3-4/2-4 M3/3) x 2 = 63-44. The first incisors are large. In gymnures, there are three pairs of incisors in each jaw, while hedgehogs have lost the third lower pair. The muzzle or rostrum of hedgehogs is shorter than in the gymnures, which have retained a narrow, shrew-like snout.

A Malayan moonrat (Echinosorex gymnura) foraging for insects in Southeast Asia. (Photo by N. Smythe/Photo Researchers, Inc. Reproduced by permission.)

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