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{{Short description|Piece of skin that has become thickened}}
[[File:Baboon buttocks.jpg|thumb|Ischial callosity on a [[baboon]]]]
A '''callosity''' is a type of [[callus]], a piece of [[skin]] that has become thickened as a result of repeated contact and friction.

== Primates ==
[[File:Sulawesi trsr DSCN0572 v1.JPG|thumb|Ischial callosities on a Sulawesi crested macaque [[Celebes crested macaque|''Macaca nigra'']]]]

All [[Old World monkey]]s, [[gibbon]]s, and some [[chimpanzee]]s have pads on their rears known as ''[[ischium|ischial]] callosities''.<ref>{{cite web|url=https://monkeybuiznezz.wordpress.com/tag/ischial-callosities/|title=Ischial callosities|publisher=MonkeyBuiznezz|accessdate=2014-02-12}}</ref><ref name="Fleagle2013">{{Cite book |title=Primate adaptation and evolution |last=Fleagle |first=John G. |date=2013 |publisher=Elsevier/Academic Press |isbn=9780123786326 |edition=3rd |location=Amsterdam |oclc=820107187}}</ref> The pads enable the monkeys to sleep sitting upright on thin branches, beyond reach of predators, without falling. Humans do not possess ischial callosities due to the [[gluteal muscles]] being large enough to provide the same cushioning.<ref>{{Cite journal |last=Montagu |first=Ashley |date=1966-10-03 |title=The Buttocks and Natural Selection |url=https://doi.org/10.1001/jama.1966.03110140101027 |journal=JAMA |volume=198 |issue=1 |pages=51 |doi=10.1001/jama.1966.03110140101027 |pmid=5953162 |issn=0098-7484|url-access=subscription }}</ref>

The ischial callosities are one of the most distinctive pelvic features which separates [[Old World monkey]]s from [[New World monkey]]s.<ref>Steudel (1981), p 399</ref>

== Right whales ==
[[File:Moira Brown - MWB 0195-NEA-S4.jpg|thumb|left|Callosities on a [[North Atlantic right whale]]]]

In [[whale]]s, callosities are rough, calcified skin patches found on the heads of the three species of [[right whale]]s. Callosities are a characteristic feature of the whale genus ''[[Eubalaena]]''. Because they are found on the head of the whale and appear white against the dark background of the whale's skin, they allow the reliable identification of individuals of the species.

The callosities themselves are grey, but their white appearance is due to large colonies of [[whale louse|whale lice]], [[whale barnacle]]s and parasitic worms which reside on them.<ref name="NEAQ">{{cite web |url=http://www.neaq.org/conservation_and_research/projects/endangered_species_habitats/right_whale_research/right_whale_background/identify_a_right_whale/callosities.php |title=Callosities |website=New England Aquarium |accessdate=24 August 2014 |archive-url=https://web.archive.org/web/20141122013247/http://www.neaq.org/conservation_and_research/projects/endangered_species_habitats/right_whale_research/right_whale_background/identify_a_right_whale/callosities.php |archive-date=2014-11-22 |url-status=dead }}</ref><ref name="CoolA">{{cite web |url=http://www.coolantarctica.com/Antarctica%20fact%20file/wildlife/whales/right_whale.htm |title=Right whales |author=Ward, Paul|date=2001|website=Cool Antarctica |accessdate=24 August 2014}}</ref> Young whales and diseased individuals are often infested with a different species of cyamid, which gives the callosities on those whales an orange hue rather than white.<ref name="CoastalStudies">{{cite web |url=http://coastalstudies.org/right-whale-research/ |title=Right Whale Research |website=Center for Coastal Studies, Provincetown, MA |accessdate=24 August 2014}}</ref> Callosities arise naturally and are present even in late-term whale fetuses, although the work of lice digging into the surface of the skin may make them more jagged and hard over time.{{Citation needed|date=August 2014}}

Callosities are found on the upper surface of the whale's head: above the eyes, on the jawline and chin, and surrounding the blowholes.<ref name="CoastalStudies"/> Callosities form a unique pattern on every right whale and, although callosities which are overgrown break off, the patterns do not change over a lifetime.<ref name="NEAQ"/>

The evolutionary significance of callosities is unknown. Male right whales have a higher density of callosities than females. Males have been observed scratching one another with their callosities and it has been suggested by Payne & Dorsey (1983) that they are a sexually dimorphic feature, used for intra-specific sexual aggression.<ref name="PayneDorsey1983">{{cite book |url=http://www.icb.org.ar/descargas/Sexual%20dimorphism%20and%20aggressive%20use%20of%20callosities%20in%20right%20whales%20(Eubalaena%20australis).pdf |chapter=Sexual dimorphism and aggressive use of callosities in right whales (Eubalaena australis) |last1=Payne |first1=Roger |first2=Eleanor M. |last2=Dorsey |title=Communication and Behaviour of Whales |year=1983 |pages=295–329 |accessdate=24 August 2014}}</ref> That explanation is not entirely satisfactory, because it does not account for the appearance of callosities in females.{{Citation needed|date=June 2010}} It has also been proposed that the barnacles attached to callosities are important in helping fend off attacks by [[orca]]s.<ref>{{cite web |last1=Hayashi |first1=Ryota |title=Past biodiversity: Historical Japanese illustrations document the distribution of whales and their epibiotic barnacles |url=https://www.researchgate.net/publication/265049647 |publisher=University of Tokyo |access-date=2021-06-28 |archive-url=https://web.archive.org/web/20160214211208if_/https://www.researchgate.net/profile/Ryota_Hayashi2/publication/265049647_Past_biodiversity_Historical_Japanese_illustrations_document_the_distribution_of_whales_and_their_epibiotic_barnacles/links/5462c32a0cf2c0c6aec1b8bd.pdf?origin=publication_list |archive-date=2016-02-14}}</ref>

== See also ==
* [[Callus]]

== Notes ==
{{Reflist}}

==References==
* {{cite journal
| url = http://www.zoology.wisc.edu/labs/hll/pdf/Steudel%201981%20functional%20aspects%20of%20pelvic%20structure.pdf
| title = Functional Aspects of Primate Pelvic Structure: A Multivariate Approach
| journal = American Journal of Physical Anthropology
| issue = 3
| pages = 399–410
| year = 1981
| first = K
| last = Steudel
| pmid = 6791507
| doi = 10.1002/ajpa.1330550314
| volume = 55
| access-date = 2009-07-19
| archive-url = https://web.archive.org/web/20100610033030/http://www.zoology.wisc.edu/labs/hll/pdf/Steudel%201981%20functional%20aspects%20of%20pelvic%20structure.pdf
| archive-date = 2010-06-10
| url-status = dead
}}
*''Callosities'' by Mason T. Weinrich in the ''Encyclopedia of Marine Mammals''. {{ISBN|0-12-551340-2}}.
*[http://www.encyclopedia.com/doc/1O8-ischialcallosity.html A Dictionary of Zoology 1999, Oxford University Press 1999]
*"On Butts and Baboons"''. ''Artsibasheva, A.'' http://monkeybuiznezz.wordpress.com/2012/09/27/on-butts-and-baboons/ [[Category:Cetaceans]]

[[Category:Animal anatomy]]
[[Category:Cetacean anatomy]]
[[Category:Primate anatomy]]
[[Category:Primates]]

Callosity - Revision history

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