OPEN The odd-toed ungulates (Order Perissodactyla) include horses, rhinoceroses, and tapirs. Odd-toed ungulates (perissodactyls) are hoofed mammals with feet that are symmetrical around a plane of symmetry that runs through their third toe. Most species are plant-eaters (herbivores). They are distributed throughout Africa, North America, South America, and Asia. A few species of perissodactyls have horns (for example, rhinoceroses). These horns are an outgrowth of skin (so they are considered dermal in origin) and consist of compressed keratin (a fibrous protein that occurs in hair, nails, feathers, and horns) Including zebras in this group.