Mammals across various species have evolved specialized cranial appendages, bony structures that protrude from the skull and serve various purposes, from defense to dominance display. These head ornaments are broadly categorized into horns and antlers, and they are typically not present when the animal is born. In most horned mammals, these structures begin as small buds or develop a significant time after birth, allowing for a safer passage through the birth canal. This general rule makes the exception stand out, prompting a closer look at the single animal whose specialized headgear is already formed at the moment of its arrival.
The Unique Answer: The Giraffe
The giraffe is the only animal known to be born with pre-existing, horn-like structures on its head. These unique appendages are not classified as true horns but are instead called ossicones, a specialized form of headgear found exclusively within the Giraffidae family. Both male and female calves possess these structures, which are typically found as a pair on the parietal bones of the skull. This early presence distinguishes the giraffe from all other horned or antlered species.
When a giraffe calf is delivered, its ossicones are in a unique state to ensure a safe birth. They consist of soft, cartilaginous tissue and are not yet fused to the underlying skull bone. The ossicones also lie flat against the calf’s head, which significantly reduces the risk of injury during the birthing process. They are covered in skin and a fine layer of hair, giving them a padded appearance. This distinctive developmental timing is the reason the giraffe stands alone among mammals with cranial ornaments.
Ossicones: Distinct from Horns and Antlers
The biological make-up of the ossicone sets it apart from the more common forms of headgear found in other ungulates. Ossicones are permanent, bony core structures that develop from ossified cartilage. Crucially, they remain covered in skin and hair throughout the giraffe’s life, distinguishing them from true horns. This permanent, living skin covering contains blood vessels and nerves, making ossicones a highly vascularized structure.
True horns, found on animals like cattle, sheep, and antelopes (Bovidae family), are also permanent structures with a core of bone. This bony core is covered by a sheath made of keratin, the same material found in human fingernails. Unlike the giraffe’s skin-covered ossicones, this keratin sheath is hard, generally unbranched, and is never shed. The growth of true horns typically begins as bony growths that fuse to the frontal bones of the skull well after birth.
Antlers, characteristic of the deer family (Cervidae), represent a third type of cranial appendage. Antlers are composed of pure bone and are temporary structures that are shed and regrown annually. While growing, antlers are covered in a soft, vascularized skin known as velvet, which is eventually rubbed off, leaving the exposed bone. The contrast is clear: antlers are shed bone, true horns are bone with a keratin sheath, and ossicones are permanent bone cores covered with living skin.
Development and Function of These Structures
The initial, soft state of the ossicones does not last long after birth. Following birth, the structures begin a process of ossification, transforming the soft cartilage into bone. Over the first few years of life, the ossicones grow and eventually fuse to the parietal bones of the giraffe’s skull. This fusion process is generally completed when the giraffe reaches sexual maturity, typically between three and five years of age.
The presence of the skin and a rich blood supply gives the ossicones an important secondary function in thermoregulation. The blood circulating through the skin covering can be cooled down, helping the giraffe regulate its body temperature in the warm African climate. Beyond this physiological role, the ossicones serve as weapons and visual signals, particularly for males. Adult males use their heavily-boned heads, weighted by the ossicones, in ritualized combat known as “necking,” where they swing their necks to strike opponents. These powerful blows establish dominance and secure mating rights. Over years of intense necking, the hair and skin at the tips of the male ossicones often become bald and knobbed, providing a physical indicator of age and fighting experience.