Giraffes are among the most recognizable animals, known for their remarkable height and distinctive patterns. These towering mammals capture attention with their long necks and legs, but their heads also feature unique structures that spark curiosity. These fascinating growths on a giraffe’s head are not horns or antlers, but rather specialized features integral to their biology and social lives.
What Are Ossicones?
The “nubs” on a giraffe’s head are scientifically termed ossicones. These are columnar or conical bony structures covered permanently in skin and fur. Unlike the horns of cattle or the antlers of deer, ossicones develop from ossified cartilage throughout the giraffe’s life. They are unique to giraffes and their closest living relative, the okapi, distinguishing them from other hoofed mammals. Ossicones are highly vascularized and innervated, containing a rich supply of blood vessels and nerves.
Formation and Development
Giraffes are born with ossicones already present, though they are soft and lie flat against the skull at birth. This initial flexibility is important to prevent injury to the mother during the birthing process. Over time, these structures gradually harden through a process called ossification, transforming from cartilage into bone. The ossicones then fuse to the skull as the giraffe matures, typically by the age of three to five years.
Ossicone development differs between male and female giraffes. Males develop thicker and more prominent ossicones that continue to grow larger and heavier throughout their lives. The tops of male ossicones often become bald or worn due to frequent use in social interactions. Female ossicones tend to remain thinner and typically retain a tuft of hair on top.
Role and Significance
Ossicones primarily serve in social interactions and combat among males. Male giraffes engage in a behavior known as “necking,” where they swing their powerful necks and use their heads, including the ossicones, as clubs to strike opponents. These forceful blows help establish dominance hierarchies and secure mating rights within a group. The bony nature and increasing weight of ossicones in males contribute to the effectiveness of these impacts.
Beyond combat, ossicones function as visual signals of maturity and status. Larger, more developed ossicones in males can indicate strength and experience, which may influence female mate selection. Some researchers hypothesize that the rich blood supply and nerve bundles within ossicones might also play a role in thermoregulation, helping to dissipate heat.
Variations Among Giraffe Species
Ossicones vary in number, shape, and size across different giraffe species and subspecies. While all giraffes possess a primary pair of ossicones on the parietal bones of their skull, some individuals, especially males, can develop additional bony protrusions. These may include a single median ossicone on the frontal bone, which can be more prominent in northern giraffe species, or smaller occipital and orbital ossicones.
These variations can aid in distinguishing between different giraffe species. For example, the northern and reticulated giraffes often have larger median ossicones compared to the Masai and southern giraffes. The overall morphology of ossicones, including their thickness and the presence of bald spots, can also help differentiate between sexes and even indicate the age of an individual giraffe.