The ears are short. The feet are narrow. The forefoot has four digits and the hind foot has five. The claws are short, and some stiff, bristlelike hairs are associated with the claws of the hind foot. The incisors are fairly narrow, and the cheek teeth are high-crowned and rooted.
Females usually have three pairs of mammae, but sometimes there are only two pairs.
The mammae are lateral, placed high up on a level with the shoulder blades, enabling the young to suckle from the side when hiding in narrow rock crevices. The dassie rat is associated with rocky areas on hills and mountains. It generally emerges from its rock shelter during the day, especially in the early morning and late afternoon, but occasionally forages after sunset. While resting or sunning itself, it generally selects a spot under a projecting rock that provides protection from attack by birds of prey. Petromus usually moves on the rocks by running, rather than jumping, but does occasionally spring from one rock to another.