There is no fossil or photographic evidence that unicorns exist. Scientists have described rare cases of single, centrally located horns in deer and cattle, and Ringling Brothers and Barnum & Bailey Circus exhibited a surgically altered, one-horned goat in 1985.
Historians believe that the original concept of the unicorn as a single-horned, horselike or deerlike creature arose from travelers' descriptions of antelope, rhinoceros or extinct animals, such as the aurochs or elasmotherium. Pre-medieval artists generally presented their figures only in profile, making it impossible to tell if a pictured animal had one horn or two. Medieval merchants often sold narwhal tusks as unicorn horns for medicinal or protective purposes.