Physical characteristics

With the exception of those in the genera Isothrix and Trichomys and those in the subfamily Dactylomyinae, all

Spiny rats (Proechimys sp.) have stiffened guard hairs on their backs and rumps. (Photo by Tom McHugh at Bronx Zoo/Photo Researchers, Inc. Reproduced by permission.)

members of this family have spines in their fur, most notably on the mid-back and rump. Each spine consists of a single modified hair, and may be fine and needle-like or broad and stout. No matter what their shape or size, these spines narrow at the base to a narrow waist where they emerge from the skin.

The forefoot characteristically has only four functioning toes, with the fifth (the pollex, equivalent to the human thumb) being vestigial. The head is often large in proportion to the body, the nose is prominent, and the snout is blunt. The ears are small in proportion to the body. Many terrestrial genera have the ability to shed their tails. The family name is derived from the Greek ekhinos, a hedgehog, and mus, a mouse.

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