View source for Ossicone

{{Short description|Horn-like structure on some animal heads}}
{{Distinguish|Ossicles}}
[[File:South African Giraffe, head.jpg|thumb|right|Ossicones of a [[giraffe]]]]
[[File:Okapi (Okapia johnstoni) 2009-04-04 01.jpg|thumb|right|Ossicones of a male [[okapi]]]]

'''Ossicones''' are columnar or conical skin-covered bone structures on the heads of [[giraffe]]s, male [[okapi]], and some of their extinct relatives. Ossicones are distinguished from the superficially similar structures of [[Horn (anatomy)|horns]] and [[antler]]s by their unique development and a permanent covering of skin and fur.

==Structure==
Giraffe ossicones consist of a highly vascularized and innervated bone core covered with similarly vascularized and innervated skin.<ref name=":0">{{Cite journal|last1=Ganey|first1=Tim|last2=Ogden|first2=John|last3=Olsen|first3=John|date=1990|title=Development of the giraffe horn and its blood supply|url=https://onlinelibrary.wiley.com/doi/abs/10.1002/ar.1092270413|journal=The Anatomical Record|language=en|volume=227|issue=4|pages=497–507|doi=10.1002/ar.1092270413|pmid=2393101|s2cid=31065446|issn=1097-0185|url-access=subscription}}</ref> They are attached to the skull with vascularized, innervated connective tissue.<ref name=":0" />  Ossicones are formed at late gestation, but in early development they are not bony and not fused to the skull yet. Ossicones usually fuse to the skull at sexual maturity.<ref name=":0" /><ref>{{Cite journal|last=Nasoori|first=A|date=2020|title=Formation, structure, and function of extra-skeletal bones in mammals|url=https://archive.org/details/formation-structure-and-function-of-extra-skeletal-bones-in-mammals|journal= Biological Reviews|volume=95|issue=4|pages=986–1019|doi=10.1111/brv.12597|pmid=32338826|s2cid=216556342}}</ref>

All male and female giraffes have a pair of parietal ossicones on the parietal bones of the skull.<ref name=":1">{{Cite journal|last=Spinage|first=C. A.|date=1968|title=Horns and Other Bony Structures of the Skull of the Giraffe, and Their Functional Significance|url=https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1365-2028.1968.tb00900.x|journal=African Journal of Ecology|language=en|volume=6|issue=1|pages=53–61|doi=10.1111/j.1365-2028.1968.tb00900.x|bibcode=1968AfJEc...6...53S |issn=1365-2028|url-access=subscription}}</ref> Males also usually have a single median ossicone on the frontal bone that is larger in northern animals and smaller in southern giraffes.<ref name=":1" /> Giraffes can also have small additional paired occipital ossicones on the occipital bones, paired orbital ossicones associated with eyes, and azygous ossicones.<ref name=":1" />

In giraffes, male and female ossicones vary in structure and purpose (a manifestation of [[sexual dimorphism]]). Males typically have thicker ossicones that become bald on top due to frequent, high-intensity [[Giraffe#Necking|necking]].<ref name="behaviour">{{cite journal |doi=10.1163/156853966x00155 |title=The Evolution of Horn-Like Organs |journal=Behaviour |volume=27 |issue=1 |pages=175–214 |year=1966 |last1=Geist |first1=Valerius }}</ref> In okapi, the male's ossicones are smaller in proportion to the head, and taper towards their tips, forming a sharper point than the comparatively blunt giraffe ossicone. Whereas female giraffes have reduced ossicones, female okapi lack ossicones entirely.

The morphology of ossicones in the extinct relatives of giraffes and okapi varies widely. Some species had two pairs of ossicones rather than one (e.g. ''[[Giraffokeryx]]''), some had rugged textures (e.g. ''[[Shansitherium]]''), and some had large, flattened ossicones (e.g. male ''[[Prolibytherium]]'').

==Function==
Similar to species with horns or antlers, male giraffes use their ossicones as weapons during combat, where they use their heads as clubs: the ossicones add weight and concentrate the force of impact onto a small area, allowing it to deliver heavier blows with higher contact pressure.<ref name="behaviour" /> The nerve bundles and large blood supply in the ossicones have led some researchers to speculate that the structures may also play a role in thermoregulation.<ref name=":0" />

==Examples==
[[File:Shansitherium fuguensis.JPG|thumb|right|Illustration of extinct ''[[Shansitherium]]'' species and ''[[Palaeotragus microdon]]'' (Giraffidae), showing a diversity of ossicone shapes and sizes no longer seen in extant animals]]

Ossicones are only found in some members of the superfamily [[Giraffoidea]], which includes the family [[Giraffidae]] (to which giraffes, okapi, and extinct relatives belong) and the entirely extinct family [[Climacoceratidae]].<ref>Hadar Picture Gallery. [http://faculty.washington.edu/ggeck/EcksGallery/EckPict13.html An ossicone of the extinct, giant, short-necked giraffe]. ''University of Washington''.</ref> It had been argued that the so-called ossicones known from fossils were actually horns, but later research showed that these structures are consistent with the ossicones of giraffes and okapi.<ref>{{cite journal |doi=10.2307/1381645 |jstor=1381645 |title=Prevalence of Ossicones in Giraffidae (Artiodactyla, Mammalia) |journal=Journal of Mammalogy |volume=69 |issue=4 |pages=845–8 |year=1988 |last1=Solounias |first1=N }}</ref> The following is a list of some ossicone-bearing [[Genus|genera]]:

; Giraffidae
* {{Extinct}}''[[Bramatherium]]'' (2 pairs)
* {{Extinct}}''[[Decennatherium]]'' (1 pair)
* ''[[Giraffa]]'' (giraffes; 1 pair)
* {{Extinct}}''[[Giraffokeryx]]'' (2 pairs)
* {{Extinct}}''[[Honanotherium]]'' (1 pair)
* {{Extinct}}''[[Injanatherium]]'' (2 pairs) – Angled horizontally relative to head
* {{Extinct}}''[[Mitilanotherium]]'' (1 pair)
* ''[[Okapia]]'' (okapi; 1–0 pairs) – Females lack ossicones
* {{Extinct}}''[[Palaeotragus]]'' (1–0 pairs) – Some species lacked ossicones
* {{Extinct}}''[[Samotherium]]'' (1 pair)
* {{Extinct}}''[[Shansitherium]]'' (1 pair)
* {{Extinct}}''[[Sivatherium]]'' (2 pairs)

; Climacoceratidae
* {{Extinct}}''[[Climacoceras]]'' (1 pair)
* {{Extinct}}''[[Prolibytherium]]'' (1 pair) – Male ossicones plate-like; females more typical

==References==
{{Reflist}}

==Further reading==
{{Spoken Wikipedia|Ossicone.ogg|date=2019-7-26}}

* {{cite journal |last1=Hou |first1=Sukuan |first2=Melinda |last2=Danowitz |first3=John |last3=Sammis |first4=Nikos |last4=Solounias |title=Dead ossicones, and other characters describing Palaeotraginae (Giraffidae; Mammalia) based on new material from Gansu, Central China |journal=Zitteliana |year=2014 |volume=32 |pages=91–8 |url=https://epub.ub.uni-muenchen.de/22389/ }}
* {{cite journal |doi=10.2307/1382004 |jstor=1382004 |title=Evidence for the Presence of Ossicones in Giraffokeryx punjabiensis (Giraffidae, Mammalia) |journal=Journal of Mammalogy |volume=72 |issue=1 |pages=215–7 |year=1991 |last1=Solounias |first1=N |last2=Moelleken |first2=S. M. C }}
* {{cite book |doi=10.1007/978-1-4613-8966-8_5 |chapter=Cranial Appendages of Giraffoidea |title=Horns, Pronghorns, and Antlers |pages=180–94 |year=1990 |last1=Churcher |first1=Charles S |isbn=978-1-4613-8968-2 }}
* {{cite journal |doi=10.1098/rspb.2011.0938 |jstor=41315010 |pmid=21733893 |pmc=3151718 |title=Evolution of ruminant headgear: A review |journal=Proceedings of the Royal Society B: Biological Sciences |volume=278 |issue=1720 |pages=2857–65 |year=2011 |last1=Davis |first1=E. B |last2=Brakora |first2=K. A |last3=Lee |first3=A. H }}
**{{lay source |template=cite web |title=Ruminant headgear: Antlers, horns, ossicones and pronghorns may offer medical clues |url=https://www.sciencedaily.com/releases/2011/07/110706093912.htm |website=ScienceDaily |date=July 10, 2010}}
* {{cite journal |doi=10.1371/journal.pone.0185139 |pmid=28926638 |pmc=5605118 |title=The earliest ossicone and post-cranial record of Giraffa |journal=PLOS ONE |volume=12 |issue=9 |pages=e0185139 |year=2017 |last1=Danowitz |first1=Melinda |last2=Barry |first2=John C |last3=Solounias |first3=Nikos |bibcode=2017PLoSO..1285139D |doi-access=free }}
* {{cite journal |doi=10.1371/journal.pone.0185378 |pmid=29091914 |pmc=5665556 |title=A new giraffid (Mammalia, Ruminantia, Pecora) from the late Miocene of Spain, and the evolution of the sivathere-samothere lineage |journal=PLOS ONE |volume=12 |issue=11 |pages=e0185378 |year=2017 |last1=Ríos |first1=María |last2=Sánchez |first2=Israel M |last3=Morales |first3=Jorge |bibcode=2017PLoSO..1285378R |doi-access=free }}

[[Category:Mammal anatomy]]