While on safari recently, I was looking at about thirty giraffes, and I was surprised at how long the horn-like structures were on some of them. I spoke to the guide and got some excellent information about these structures, called ossicones.
Ossicones are unique to the Giraffidae family. They are not horns or antlers but permanent, bony growths that eventually fuse to the skull. Ossicones are found in both male and female giraffes, though the ossicones of male giraffes are larger and continue to grow longer than females.
If you want to know more about giraffe ossicones, please read on.
Do giraffes have horns or antlers?
The two structures on a giraffe’s head are called ossicones. Ossicones are exostoses—bone formations that grow on existing bone found on giraffe skulls. While many liken ossicones to horns or antlers, they have several differences from these growths that make them a unique anatomical feature in giraffes and the closely related okapi.
Ossicones differ from antlers—a feature of the Cervidae or deer family—in that they are permanent fixtures in the skull, and they are not restricted to the male sex. The primary difference between ossicones and horns—a feature of the Bovidae family—is that ossicones lack a sheath made of keratin, which is a feature in the typical horns seen on cows, goats, bison, and other bovids.
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Do male and female giraffes have ossicones?
As previously alluded to, ossicones can be found in male and female giraffes. Though both sexes have ossicones present, these features have develop differently in male and female giraffes.
It takes a considerable amount of time for the bone of the ossicones to fuse to the skulls of giraffes. In the case of males, it typically takes just over four years of age, whereas it takes nearly twice that amount—at least seven years of age—in female giraffes. Fusion of the ossicones to the skull does not limit their growth in males, but the ossicones of most females cease to grow after they have become fused to the skull.
The ossicones of male giraffes can vary significantly among individuals and subspecies, as they measure between 10 and 25 cm in length while growing to a circumference of up to 22 cm. Female ossicones are seldom comparable in size to those of males, as their ossicones rarely continue to deposit bone and grow after fusion to the skull. Consequently, female ossicones tend to be thinner and narrower than those seen in males.
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Anatomy and development of ossicones
Ossicones begin to grow in the foetus of a giraffe-a characteristic not seen in Bovidae or Cervidae and is thus novel as far as mammals go. It is unclear when precisely the ossicones begin to develop within a foetus, but researchers have discovered them in foetuses as young as ten months old.
Though ossicones are composed entirely of bone in adult giraffes, they contain cartilaginous pockets as they develop in giraffe foetuses. Ossicones are about an inch long in a newborn giraffe. They begin to ossify after a giraffe has been born- a process initiated by connective tissue that attaches the ossicone to the skull.
Ossicones are covered with a layer of furry skin to which a small number of bristle-like hairs are attached. Neither the skin nor the hairs are shed during a giraffe’s life, though hairs may be lost due to old age.
The skin on the tips of the ossicones often wears down in males as a result of combat with other males. The skin that covers the ossicones is vascularized, and a regular supply of blood flows through this layer of skin.
The specific parts of the skull to which ossicones fuse are the parietal bones. Because ossicones fuse to the parietal bones, they are sometimes referred to as “parietal horns.” Giraffes have the potential to grow other horn-like projections on their heads, with the median horn being the most common growth aside from ossicones.
Median horns may appear as a bump on the centre of a giraffe’s nose. Median horns are not present in all giraffes, and it has been found that these bone projections may vary depending on sex and subspecies. Median horns, like ossicones, are not true horns and are instead projections of bone that eventually fuse to a giraffe’s skull.
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Why do giraffes have ossicones?
Male giraffes derive much more use from their ossicones than females. Once male giraffes reach sexual maturity, they follow females around and determine when a female is ready to mate. Once a female reaches optimal fertility levels, males will compete with one another for the chance to reproduce.
Such competition among males makes good use of the ossicones, as these bony growths can easily be turned into weapons during combat. Male giraffe fighting is referred to as “necking”, and it is a process by which males deliver powerful blows with their head and neck to opposing males. Ossicones can be used to bludgeon the competition as a giraffe swings its head and neck into the body of another male.
The fact that male giraffes use their ossicones in such a way explains why ossicones continue to grow throughout a male’s lifetime. The larger the ossicones, the more powerful the bony growths become.
Female giraffes do not seem to use their ossicones in any way. Females do not compete with one another, so they do not require ossicones for combat. Moreover, there have been no documented instances in which ossicones have been used to fend off predators, as giraffes use their legs to defend themselves if necessary.
Although scientists have not documented female giraffes making explicit use of their ossicones, they may benefit a giraffe in ways that are not yet understood by science.
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Conclusion
A layer of vascularized skin, fur, and hair cover the ossicones, though these components may wear down with time. Male giraffes use their ossicones during combat with other males, while females are not known to use them for any particular purpose. Ultimately, ossicones are a unique anatomical feature, and there is still much to learn about these bony growths.
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Works Cited
Do all giraffe have horns? Giraffe Conservation Foundation. (2021, November 4). Retrieved May 13, 2022, from https://giraffeconservation.org/facts/do-all-giraffe-have-horns/
Peterson, D., & Ammann, K. (2013). Giraffe reflections. Univ. of California Press.
Shorrocks, B. (2016). The Giraffe: Biology, ecology, evolution and behaviour. Wiley Blackwell.
World Deer. (2021, October 24). Antler vs horn comparison [what are the differences?]. Antler vs Horn Comparison. Retrieved May 13, 2022, from https://worlddeer.org/antler-vs-horn/