Development of the giraffe horn and its blood supply

Abstract

The giraffe horn is an unusual cranial exostosis that lacks clear delineation and categorization as either horn or antler. The distinction between the two is made by contrasting their methods of development and basic composition. This process of development has not been detailed in the giraffe, a factor contributing to the difficulty in distinguishing the classification of these horns. In a chronological series of giraffe horns from prenatal and postnatal animals, we have observed unique morphologies that define their proper location on the skull, the blood supply to them, and the transitions involved in their histological development. While our observations have facilitated the classification of the giraffe horn, our interpretations were not always in accord with previous reports.

Evolution of ruminant headgear: a review

“…[24,29]) as well as to headgear per se (e.g. [11]), we restrict its use to bovid horns (headgear covered in a keratinous sheath that is not annually replaced).…”

“…The ossicone begins as a separate bony core above the frontoparietal suture in giraffes and above the frontals in okapis [22]. The ossicone was originally thought to condense as fibrocartilage within the skin above the bone [26,27]; however, Ganey et al [24] showed that it is primarily non-cartilaginous. Although initial ossification occurs dermally, the process is intramembranous, as is typical for skull roof bones [24].…”

“…Horns (figure 2b), found only in bovids, are composed of a scabbard-like keratinous sheath covering a bony horncore, neither of which is ever shed [14,21]. Ossicones (figure 2c), found only in giraffids today ( [22], but see [23]), are the simplest form of extant headgear, consisting of bony projections of dermal bones covered by skin and hair [22,[24][25][26][27]. Finally, pronghorns (figure 2d), found only in Antilocapra americana today, are projections of the frontals that are covered by skin, hair and an annually replaced keratinous sheath [22,[28][29][30][31].…”

A quantitative comparative analysis of the size of the frontoparietal sinuses and brain in vombatiform marsupials

“…For example, if brain size scales negatively with skull size, sinuses may expand to fill the frontal bone to increase the surface area for attachment of masticatory muscles in large animals. Other hypotheses include decreasing the weight of the skull (Davis et al, 1996;Mitchell and Skinner, 2003;Shea, 1936), providing thermoregulation of the brain (Bremer, 1940;Dyce et al, 2002;Ganey et al, 1990;Skinner, 2003, 2004), shock absorption during head-butting or neck-sparring (Badlangana et al, 2011;Davis et al, 1996;Schaffer and Reed, 1972), serving as a resonance chamber for the production of low frequency sounds (Leakey and Walker, 1997;von Muggenthaler et al, 1999) and dissipation of stress over the skull during mastication, and particularly bone-cracking in carnivores (Buckland-Wright, 1971, 1978Joeckel, 1998;Tanner et al, 2008). Nonetheless, hypotheses regarding sinus function are difficult to test without first obtaining data on sinus variation within and between species.…”

Comparisons of Schansitherium tafeli with Samotherium boissieri (Giraffidae, Mammalia) from the Late Miocene of Gansu Province, China

“…The modern giraffe possesses exceptionally elongated cervical vertebrae and metapodials; the extinct taxa exhibit varying degrees of neck and limb elongation [4–6]. Giraffidae possess specialized cranial appendages termed ossicones, which start as separate ossifications that subsequently fuse to the skull [2, 7–9]. Among the Giraffidae, several taxa exhibit atypical ossicone structure, including the sivatheres Sivatherium and Bramatherium and the samothere Schansitherium .…”