Animals in the order Artiodactyla are known as the even toed animals. Artiodactyls are sometimes called cloven hooved, that is they have two toes. Artiodactyla skulls come in many shapes and forms. Those found in Old World pigs are large and massive with large upper canines that grow outward and backwards forming tusks. The skull of the New World equivalent of a pig, the peccary, is small and more delicate. Its canines grow downward and meet with the lower canines to form precision scissors. Animals of the order Artiodactyla may have antlers or horns. Deer have antlers. Antlers are only grown by the males, with the exception of caribou in which both sexes carry them. Antlers are shed each year.

Animals such as antelopes, goats, bison, sheep and cattle do not shed their horns. The one exception is the pronghorn which sheds its horns annually. Horns are permanent and continue to grow throughout the animal's lifetime. Horns are grown by all adult bovid males and by females of most genera. A horn is composed of a bony core that is covered with a hard sheath of horny material called "keratin." Your fingernails and hair are also made of keratin.