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Odd-toed ungulates | Perissodactyla
Onevenhoevigen | Perisodáctilos
Ungulates in which the third toe forms the axis of the foot and carries the weight; in the horses it is the only one left, and its nail has become a hoof. The lower leg is a single long bone with nothing but tendons around it — light, long-striding, built for keeping going in open country rather than for turning. The cheekteeth are very high-crowned, their enamel intricately folded to withstand the silica in grass, and as they wear they push further out of the jaw. Digestion happens behind the stomach, in a very capacious caecum and colon: the food passes through quickly, so a poor and woody ration is dealt with not by digesting it better but by eating more of it — a horse can live on grass that would starve a ruminant. A single foal is born after about a year, and is on its feet and following within the hour.
Families in this order
- Horses and asses | Equidae1 speciesOnly the third toe of each foot is left, and its nail has become a hoof: a horn wall growing down from the coronet, carrying on the underside an elastic frog that is pressed in at every stride and helps drive the blood back up. Upper and lower incisors meet squarely and clip grass close to the ground — closer than a ruminant can. Behind a toothless gap stand six very high cheekteeth in each half of the jaw. A mane on the neck and long hair in the tail are family traits, as are a broad range of neighs, brays, snorts and squeals and a facial expression that is readable at close quarters. Social form depends on water: where grass and water are ample, lasting bands of mares live with a single stallion; on desert steppe the stallions instead hold a territory around a drinking place and the groups are loose. One foal to a pregnancy.