Ossicone

Ossicones are horn-like or antler-like protuberances on the heads of giraffes, male okapis, and their extinct relatives, such as Sivatherium, and the climacoceratids, such as Climacoceras.[1] It has been argued that these extinct species did not have true ossicones; however, later research has revealed their ossicones to be in line with those of giraffids. Ossicones are located dorsally of the frontal bone and fuse to the skull later in life.[2]

Not to be confused with Ossicles.
Ossicones of a reticulated giraffe
Fossilised antler-like ossicone of Sivatherium maurusium

Ossicones are similar to the horns of antelopes and cattle, except that they are derived from ossified cartilage[3] or subcutaneous connective tissues rather than living bone[4] , and that the ossicones remain covered in skin and fur, rather than horny keratin. Antlers (as on deer) are derived from bone tissue: when mature, the skin and fur covering of the antlers, termed "velvet", is sloughed and scraped off to expose the bone of the antlers.

Ossicones are present at birth; however, they lie flat and are not attached to the skull in order to avoid injury at birth.[5] Male and female ossicones vary in structure and purpose. Males typically have thicker ossicones that become bald on top due to frequent necking. These ossicones also add weight to the giraffe's head allowing them to deliver heavier, sometimes fatal, blows. The added weight is an evolutionary trait bred from necessity. The addition of ossicones also leads to other evolutionary adaptations such as heavy hides and specialized dermal shields.[6]

References
  1. Hadar Picture Gallery. An ossicone of the extinct, giant, short-necked giraffe. University of Washington.
  2. Solounias, N (1988). "Prevalence of Ossicones in Giraffidae (Artiodactyla, Mammalia)". Journal of Mammalogy. 69 (4): 845–8. doi:10.2307/1381645. JSTOR 1381645.
  3. "The Nashville Zoo at Grassmere – Animals :: Masai Giraffe". Nashville Zoo at Grassmere. 30 Jun 2008. Archived from the original on 2008-06-30.
  4. Nasoori, Alireza (2020). "Formation, structure, and function of extra-skeletal bones in mammals". Biological Reviews. doi:10.1111/brv.12597.
  5. "FAQs - GiraffeConservation.org". GiraffeConservation.org. Retrieved 2018-04-26.
  6. Geist, Valerius (1966). "The Evolution of Horn-Like Organs". Behaviour. 27 (1): 175–214. doi:10.1163/156853966x00155.

Further reading


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