The only animal born with horns is the giraffe. Both male and female giraffes are born with two horn-like structures atop their heads called ossicones.
Ossicones consist of hard cartilage. When giraffes are born, the ossicones are covered in skin and a fine layer of hair. These horns are fused to the parietal area of the skull. The male ossicones are typically rounded at the top and bald, while the female ossicones are usually thinner and contain a tuft of hair on the ends.
The function of these horns is not entirely understood, but scientists believe they aid in temperature regulation. The horns are also used by the males during combat over breeding rights with female giraffes.