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A callosity is a type of
callus A callus (: calluses) is an area of thickened and sometimes hardened skin that forms as a response to repeated friction, pressure, or other irritation. Since repeated contact is required, calluses are most often found on the feet and hands, b ...
, a piece of
skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. Other animal coverings, such as the arthropod exoskeleton, have different ...
that has become thickened as a result of repeated contact and friction.


Primates

All
Old World monkey Old World monkeys are primates in the family Cercopithecidae (). Twenty-four genera and 138 species are recognized, making it the largest primate family. Old World monkey genera include baboons (genus '' Papio''), red colobus (genus '' Piliocolob ...
s,
gibbon Gibbons () are apes in the family Hylobatidae (). The family historically contained one genus, but now is split into four extant genera and 20 species. Gibbons live in subtropical and tropical forests from eastern Bangladesh and Northeast Indi ...
s, and some
chimpanzee The chimpanzee (; ''Pan troglodytes''), also simply known as the chimp, is a species of Hominidae, great ape native to the forests and savannahs of tropical Africa. It has four confirmed subspecies and a fifth proposed one. When its close rel ...
s have pads on their rears known as '' ischial callosities''. 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 The gluteal muscles, often called glutes, are a group of three muscles which make up the gluteal region commonly known as the buttocks: the gluteus maximus muscle, gluteus maximus, gluteus medius muscle, gluteus medius and gluteus minimus muscl ...
being large enough to provide the same cushioning. The ischial callosities are one of the most distinctive pelvic features which separates
Old World monkey Old World monkeys are primates in the family Cercopithecidae (). Twenty-four genera and 138 species are recognized, making it the largest primate family. Old World monkey genera include baboons (genus '' Papio''), red colobus (genus '' Piliocolob ...
s from
New World monkey New World monkeys are the five families of primates that are found in the tropical regions of Mexico, Central and South America: Callitrichidae, Cebidae, Aotidae, Pitheciidae, and Atelidae. The five families are ranked together as the Ceboi ...
s.


Right whales

In
whale Whales are a widely distributed and diverse group of fully Aquatic animal, aquatic placental mammal, placental marine mammals. As an informal and Colloquialism, colloquial grouping, they correspond to large members of the infraorder Cetacea ...
s, callosities are rough, calcified skin patches found on the heads of the three species of
right whale Right whales are three species of large baleen whales of the genus ''Eubalaena'': the North Atlantic right whale (''E. glacialis''), the North Pacific right whale (''E. japonica'') and the southern right whale (''E. australis''). They are class ...
s. Callosities are a characteristic feature of the whale genus ''
Eubalaena Right whales are three species of large baleen whales of the genus ''Eubalaena'': the North Atlantic right whale (''E. glacialis''), the North Pacific right whale (''E. japonica'') and the southern right whale (''E. australis''). They are class ...
''. 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 lice,
whale barnacle Whales are a widely distributed and diverse group of fully aquatic placental marine mammals. As an informal and colloquial grouping, they correspond to large members of the infraorder Cetacea, i.e. all cetaceans apart from dolphins and por ...
s and parasitic worms which reside on them. 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. 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. Callosities are found on the upper surface of the whale's head: above the eyes, on the jawline and chin, and surrounding the blowholes. 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. 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. That explanation is not entirely satisfactory, because it does not account for the appearance of callosities in females. It has also been proposed that the barnacles attached to callosities are important in helping fend off attacks by
orca The orca (''Orcinus orca''), or killer whale, is a toothed whale and the largest member of the oceanic dolphin family. The only extant species in the genus '' Orcinus'', it is recognizable by its black-and-white-patterned body. A cosmopol ...
s.


See also

*
Callus A callus (: calluses) is an area of thickened and sometimes hardened skin that forms as a response to repeated friction, pressure, or other irritation. Since repeated contact is required, calluses are most often found on the feet and hands, b ...


Notes


References

* *''Callosities'' by Mason T. Weinrich in the ''Encyclopedia of Marine Mammals''. {{ISBN, 0-12-551340-2.
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/ Cetaceans Animal anatomy Cetacean anatomy Primate anatomy Primates