The deserts of the southern edge of the Palaearctic realm are among the harshest environments on Earth. Vast expanses of sand, clay, rock and rubble are baked by a broiling sun during the day and frozen by cold at night. There are no barriers to the chilling winds that blow southwards from the northern icecap, or downwards from the mountain peaks in the south. Rainfall is infrequent and confined to spring and autumn. The vegetation is sparse and only appears when rain has fallen. Animals must be quite hardy to exist in such an environment, and most of the plant-eating creatures found here are cold-blooded. The slow metabolism of such herbivorous animals as tortoises and plant-eating lizards enables them to gorge themselves when the plants are available, and to sleep away the harsher times in burrows. Of the warm-blooded animals the mammals are most successful, avoiding the extreme conditions by being active only at dawn and dusk. One of the few warm-blooded dinosaurs that live here is the diminutive debaril. In its life style and, to some extent, its appearance, it parallels the desert mammals. It is active at dawn and dusk, eats roots and seeds, conserves its water efficiently and burrows in the sand.
The debaril, like most of the small, plant-eating modern dinosaurs, is descended from a hypsilophodont ornithopod. It is about 60 centimetres (2 ft) long and is well adapted to the extremes of its environment. Under cold conditions it hunches itself up to present a small surface area to the wind. The wrinkles in the skin bunch together to form an insulating coat. Heavy lids fold over the eye to prevent chilling. During cold conditions it moves in a series of bounds. When it is hot it stretches itself out, presenting a large surface area that is easily cooled, and travels by running on hind legs.