Why Do Giraffes Have Horns?

Have you noticed the small projections on the top of a giraffe’s head and assumed that they were horns? They are called ossicones and are not actually horns at all. These fascinating structures are possessed only by giraffes and okapi and have intrigued biologists for centuries. So, let’s find out more about them.

Where Are a Giraffe’s Ossicones?

Ossicones are paired structures found on a giraffe’s head but are not true horns because they lack a keratin sheath. Additionally, giraffes have more than one set of ossicones, but we usually only notice the largest pair. These are called the parietal ossicones and are found on the parietal bones (cranium bones) of the skull in both males and females. Male giraffes, however, also have a single median ossicone on the frontal bone. Some giraffes may also have small additional paired occipital ossicones on the occipital bones (at the back of the skull). There are also paired orbital ossicones near the eyes, as well as a single (azygous) ossicone located just behind one of the orbital ossicones.

What Are Ossicones?

Ossicones are permanent bony outgrowths covered with skin that has a good blood supply. They begin as nodules of bone under the skin and are initially separate from the skull bone. This classifies them as sesamoid bones, which are small, independent bones like the patella (kneecap) in humans. However, as they grow, ossicones fuse with the underlying skull bone, typically around the time the giraffe reaches sexual maturity.

Unlike antlers, ossicones are present in both sexes and are not shed. Also, their covering does not shed, unlike the velvet covering of antlers. Males have larger ossicones than females, with a circumference of around 8 inches and a length of around 7 inches. Male ossicones also often have a tuft of hair on the top. A now-extinct relative of the giraffe, called Sivatherium giganteum, which lived from the Late Miocene to Early Pleistocene, had ossicones measuring up to around three feet!

Why Do Giraffes Have Ossicones?

There is no single answer to explain the purpose of ossicones. However, the two leading theories are connected with fighting and thermoregulation.

Male giraffes follow a strict dominance hierarchy defined by age and size. One way in which they may establish which male is dominant is by fighting and sparring. They position themselves side by side and swing their long necks at their opponent, striking with their heads and ossicones. The ossicones allow the giraffe to deliver a painful blow to his opponent’s body without hurting his own head. Larger ossicones would be able to cause more damage! Because ossicones have such a rich blood supply, injuries to them tend to heal quickly.

Some scientists have also suggested that the network of blood vessels within ossicones plays a role in altering the distribution of blood around the body. They have noted that ossicones have a greater blood supply than is needed to simply nourish the skin or bony core. Therefore, it’s likely that ossicones dissipate heat and cool the giraffe down when the surroundings are hot.