Male okapi possess ossicones, a pair of supraorbital, hair-covered frontal horns that can grow up to 15 cm in length and incline posteriodorsally from the skull.
Male okapi possess permanent ossicones, a pair of supraorbital, hair-covered frontal horns that are fused to the frontal bones over the orbits and project rearward. These horns are variable in girth and length, but do not exceed 15 centimeters above the skull. The hair on the tops of these horns is often rubbed to the bone, but they do not shed.
Only male okapi possess these horns, whereas females possess hair whorls where the horns of males are located. Sometimes, however, small rudimentary horns may be present in females. There are no other cranial features of the okapi that have been found to be significantly dimorphic.
Sources: (Bodmer & Rabb, 1992; Palkovacs, 2000; San Diego Zoo Global, 2017)
Image: Tambako the Jaguar