The details of foot anatomy vary between the three groups of odd-toed hoofed mammals. Horses have lost all but a single toe, the bones of which have adapted to form a sturdy base on which to stand. Tapirs have four toes on their front feet and only three toes on their hind feet. Rhinoceroses have three hoofed toes on both their front and back feet.
The three groups of living odd-toed hoofed mammals are varied in their body structure. Horses are long-legged, graceful animals, tapirs are smaller and rather pig-like in body structure and rhinoceroses are very large and bulky in build.
Like the even-toed hoofed mammals, odd-toed hoofed mammals are herbivores but the two groups differ significantly with respect to stomach structure. Whereas most even-toed hoofed mammals (with the exception of pigs and peccaries) have a multi-chambered stomach, odd-toed hoofed mammals have a pouch that extends from the large intestine (called the caecum) where their food is broken down by bacteria. Many even-toed hoofed mammals regurgitate their food and re-chew it to aid in digestion. But odd-toed hoofed mammals do not regurgitate their food, it instead is broken down slowly in their digestive tract.
Odd-toed hoofed mammals inhabit Africa, Asia, North America and South America. Rhinoceroses are native to Africa and southern Asia. Tapirs live in the forests of South America, Central America, and Southeast Asia. Horses are native to North America, Europe, Africa and Asia and are now essentially worldwide in their distribution, due to domestication.
Some odd-toed hoofed mammals, such as rhinoceroses, have horns. Their horns form from an outgrowth of skin and consist of compressed keratin, a fibrous protein that is also found in hair, nails and feathers.
It was previously thought that odd-toed hoofed mammals were closely related to even-toed hoofed mammals. But recent genetic studies have revealed that the odd-toed hoofed mammals may in fact be more closely related to carnivores, pangolins and bats than to the even-toed hoofed mammals.