Editing Scale (zoology)

{{short description|Small rigid plate that grows out of an animal's skin}}
{{Other uses|Scale (disambiguation){{!}}Scale}}
[[File:Keeled scales on a southern watersnake (26954310414).jpg|thumb|right|250px|Keeled scales of a [[colubrid]] snake ([[banded water snake]]; ''Nerodia fasciata'')]]

In [[zoology]], a '''scale''' ({{langx|grc|[[wikt:λεπίς|λεπίς]]|lepís}}; {{langx|la|[[wikt:squama|squāma]]}}) is a small rigid [[plate (animal anatomy)|plate]] made out of [[keratin]] that grows out of [[Vertebrate]] [[animals]]' [[skin]] to provide protection. In [[lepidopterans]] ([[butterflies]] and [[moths]]), scales are plates on the surface of the [[insect wing]], made out of [[chitin]] instead of keratin, and provide coloration. Scales are quite common and have evolved multiple times through [[convergent evolution]], with varying structure and function.

Scales are generally classified as part of an organism's [[integumentary system]]. There are various types of scales according to the shape and [[class (biology)|class]] of an animal.

==Fish scales==
{{main|Fish scale}}Fish scales are [[skin|dermally]] derived, specifically in the [[mesoderm]]. This fact distinguishes them from reptile scales paleontologically.
Genetically, the same genes involved in tooth and hair development in mammals are also involved in scale development.<ref>{{cite journal | vauthors = Sharpe PT | title = Fish scale development: Hair today, teeth and scales yesterday? | journal = Current Biology | volume = 11 | issue = 18 | pages = R751–2 | date = September 2001 | pmid = 11566120 | doi = 10.1016/S0960-9822(01)00438-9 | s2cid = 18868124 | doi-access = free }}</ref><gallery mode="packed">
File:Ganoid scales.png|Ganoid scales on a [[carboniferous]] fish ''[[Amblypterus]] striatus''
File:Denticules cutanés du requin citron Negaprion brevirostris vus au microscope électronique à balayage.jpg|Placoid scales on a [[lemon shark]] (''Negaprion brevirostris'')
File:RutilusRutilusScalesLateralLine.JPG|Cycloid scales on a [[common roach]] (''Rutilus rutilus'')
</gallery>

===Cosmoid scales===<!-- This section is linked from [[Coelacanth]] -->
True [[cosmoid scale]]s can only be found on the [[Sarcopterygian]]s. The inner layer of the scale is made of [[lamellar]] bone. On top of this lies a layer of spongy or [[Blood vessel|vascular]] bone and then a layer of [[dentine]]-like material called [[cosmine]]. The upper surface is [[keratin]]. The [[coelacanth]] has modified cosmoid scales that lack cosmine and are thinner than true cosmoid scales.

===Ganoid scales===<!-- This section is linked from [[Gar]] -->
[[Ganoid scale]]s can be found on [[gar]]s (family [[Lepisosteidae]]), [[bichir]]s, and reedfishes (family [[Polypteridae]]). Ganoid scales are similar to cosmoid scales, but a layer of [[ganoin]] lies over the cosmine layer and under the enamel{{Clarify|date=January 2010}}. Ganoin scales are diamond shaped, shiny, and hard. <!-- Which is it, enamel or dentine?  Only dentine mentioned previously. --> 
Within the ganoin are [[guanine]] compounds, iridescent derivatives of guanine found in a DNA molecule.<ref>{{cite journal | vauthors = Levy-Lior A, Pokroy B, Levavi-Sivan B, Leiserowitz L, Weiner S, Addadi L | title =Biogenic guanine crystals from the skin of fish may be designed to enhance light reflectance | journal = Crystal Growth & Design | year =2008 | volume =8 | issue =2 | pages = 507–511 |doi=10.1021/cg0704753}}</ref> The iridescent property of these chemicals provide the ganoin its shine.

===Placoid scales===

[[Placoid scale]]s are found on [[Chondrichthyes|cartilaginous fish]] including [[shark]]s and [[stingray]]s. These scales, also called denticles, are similar in structure to [[tooth|teeth]], and have one median spine and two lateral spines. The modern jawed fish ancestors, the jawless [[ostracoderm]]s and later jawed [[placoderm]]s, may have had scales with the properties of both placoid and ganoid scales.

===Leptoid scales===
[[Leptoid scale]]s are found on higher-order bony fish.  As they grow they add concentric layers. They are arranged so as to overlap in a head-to-tail direction, like roof tiles, allowing a smoother flow of water over the body and therefore reducing [[Drag (physics)|drag]].<ref>{{cite book | publisher = John Wiley & Sons | isbn = 978-1-118-92421-1| last1 = Ballard| first1 = Bonnie| last2 = Cheek| first2 = Ryan | name-list-style = vanc | title = Exotic Animal Medicine for the Veterinary Technician | date = 2 July 2016 | url=https://books.google.com/books?id=h1_NDAAAQBAJ&q=leptoid+scale&pg=PT786}}</ref> They come in two forms:
*[[Cycloid scale]]s have a smooth outer edge, and are most common on fish with soft fin rays, such as [[salmon]] and [[carp]].
*[[Ctenoid scale]]s have a toothed outer edge, and are usually found on fish with spiny fin rays, such as [[Bass (fish)|bass]] and [[crappie]].

==Reptilian scales==
[[File:Gold Dust Day Gecko closeup hawaii edit 1.jpg|thumb|Brightly colored scales on a [[gold dust day gecko]]]]
{{main|Reptile scales}}

[[Reptile]] scale types include: cycloid, granular (which appear bumpy), and keeled (which have a center ridge). Scales usually vary in size, the stouter, larger scales cover parts that are often exposed to physical stress (usually the feet, tail and head), while scales are small around the joints for flexibility. Most snakes have extra broad scales on the belly, each scale covering the belly from side to side.

The scales of all reptiles have an epidermal component (what one sees on the surface), but many reptiles, such as [[crocodilian]]s and turtles, have [[osteoderm]]s underlying the epidermal scale. Such scales are more properly termed [[scute]]s. Snakes, [[tuatara]]s and many lizards lack osteoderms. All reptilian scales have a dermal papilla underlying the epidermal part, and it is there that the osteoderms, if present, would be formed.

Many reptiles possess large scales not supported by osteoderms known as feature scales. The [[green iguana]] possesses large feature scales on the ventral sides of its neck, and dorsal spines not supported by osteoderms. Many extinct non-avian [[dinosaurs]] such as [[Carnotaurus]] and [[Brachylophosaurus]] are known to possess feature scales from skin impressions.

==Avian scales==
[[File:Riesenseeadler Fang.JPG|thumb|Scales on talons of a [[Steller's sea eagle]] (''Haliaeetus pelagicus'')]] 
{{main|Bird anatomy#Scales}}
Birds' scales are found mainly on the toes and metatarsus, but may be found further up on the ankle in some birds. The scales and scutes of birds were thought to be [[Homology (biology)|homologous]] to those of reptiles,<ref name=Lucas>{{cite book |last=Lucas |first=Alfred M. | name-list-style = vanc |year=1972 |title=Avian Anatomy - integument |location=East Lansing, Michigan, USA |publisher=USDA Avian Anatomy Project, Michigan State University |pages=67, 344, 394–601}}</ref> but are now agreed to have evolved independently, being degenerate feathers.<ref name="pmid23493711">{{cite journal | vauthors = Zheng X, Zhou Z, Wang X, Zhang F, Zhang X, Wang Y, Wei G, Wang S, Xu X | title = Hind wings in Basal birds and the evolution of leg feathers | journal = Science | volume = 339 | issue = 6125 | pages = 1309–12 | date = March 2013 | pmid = 23493711 | doi = 10.1126/science.1228753 | bibcode = 2013Sci...339.1309Z | s2cid = 206544531 }}</ref><ref name="pmid12949769">{{cite journal | vauthors = Sawyer RH, Knapp LW | title = Avian skin development and the evolutionary origin of feathers | journal =  Journal of Experimental Zoology Part B: Molecular and Developmental Evolution | volume = 298 | issue = 1 | pages = 57–72 | date = August 2003 | pmid = 12949769 | doi = 10.1002/jez.b.26 }}</ref>

[[Carcharodontosauridae|Carcharodontosaurid]] [[theropod]] dinosaur [[Concavenator]], is known to have possessed these feather-derived tarsal scutes.

==Mammalian scales==
[[File:Indian pangolin (Manis crassicaudata) - oo 246940 (cropped to A).jpg|thumb|Scale-covered [[Indian pangolin]]]]
An example of a scaled mammal is the [[pangolin]]. Its scales are made of keratin and are used for protection, similar to an [[armadillo]]'s armor. They have been convergently evolved, being unrelated to mammals' distant reptile-like ancestors (since [[therapsids]] lost scales), except that they use a similar gene.

On the other hand, the [[musky rat-kangaroo]] has scales on its feet and tail.<ref>{{cite web |url=http://rainforest-australia.com/rkangaroo.htm | work = Rainforest-Australia.com |title=Musky Rat Kangaroo |access-date=2014-03-08 |url-status=dead |archive-url=https://web.archive.org/web/20131030065952/http://rainforest-australia.com/rkangaroo.htm |archive-date=2013-10-30 }}</ref> The precise nature of its purported scales has not been studied in detail, but they appear to be structurally different from pangolin scales.

[[Anomalure]]s also have scales on their tail undersides.<ref>{{cite book | veditors = Fleming T, Macdonald D | title = The Encyclopedia of Mammals | location = New York | publisher = Facts on File | page = [https://archive.org/details/encyclopediaofma00mals_0/page/632 632] | isbn = 0-87196-871-1 | year = 1984 | url = https://archive.org/details/encyclopediaofma00mals_0/page/632 }}</ref>

Foot pad epidermal tissues in most mammal species have been compared to the scales of other vertebrates. They are likely derived from cornification processes or stunted fur much like avian reticulae are derived from stunted feathers.<ref>{{cite book | first = Richard Ian Campbell | last = Spearman | name-list-style = vanc | date = 1973 | title = The integument: a textbook of skin biology | publisher = Cambridge University Press | isbn = 978-0-521-20048-6 | url-access = registration | url = https://archive.org/details/integumenttextbo00spea }}</ref>

==Arthropod scales==
{{See also|Scale (insect anatomy)}}
[[File:Luna moth scales.jpg|thumb|Scales on a [[luna moth]] (''Actias luna'')]]
[[File:Spider scale.jpg|thumb|Generalized structure of a keeled, lanceolate scale from a [[jumping spider]]]]
[[Butterflies]] and [[moth]]s - the order [[Lepidoptera]] ([[Greek language|Greek]] "scale-winged") - have membranous [[Insect wing|wings]] covered in delicate, powdery scales, which are modified [[setae]].  Each scale consists of a series of tiny stacked platelets of organic material, and butterflies tend to have the scales broad and flattened, while moths tend to have the scales narrower and more hair like.  Scales are usually [[pigment]]ed, but some types of scales are iridescent, without pigments; because the thickness of the platelets is on the same order as the [[wavelength]] of [[visible light]] the plates lead to structural coloration and [[iridescence]] through the physical phenomenon described as [[thin-film optics]]. The most common color produced in this fashion is [[blue]], such as in the ''[[Morpho (genus)|Morpho]]'' butterflies.

Some types of [[spider]]s also have scales. Spider scales are flattened setae that overlay the surface of the [[cuticle]]. They come in a wide variety of shapes, sizes, and colors. At least 13 different spider families are known to possess cuticular scales, although they have only been well described for [[jumping spider]]s (Salticidae) and [[lynx spider]]s (Oxyopidae).<ref>{{cite journal |last1=Townsend |first1=Victor R. |last2=Felgenhauer |first2=Bruce E. |title=Cuticular Scales of Spiders |journal=Invertebrate Biology |date=1998 |volume=117 |issue=4 |pages=318 |doi=10.2307/3227034|jstor=3227034 }}</ref><ref>{{cite journal |last1=Hill |first1=David E. |title=Jumping spider scales (Araneae: Salticidae) |journal=Peckhamia |date=22 October 2022 |volume=279 |issue=1 |pages=1–83 |url=http://peckhamia.com/peckhamia/PECKHAMIA_279.1.pdf}}</ref> 

Some [[crustacean]]s such as ''[[Glyptonotus antarcticus]]'' have knobbly scales.<ref>{{cite journal |author=Meyer-Rochow, V. B. |year=1980 |title=Cuticular surface structures in ''Glyptonotus antarcticus'' — a marine isopod from the Ross Sea (Antarctica) |journal=Zoomorphologie |volume=94 |issue=2 |pages=209–216 |doi=10.1007/BF01081935 |s2cid=9216365 }}</ref> Some [[crayfish]] have been shown to use antennal scales that are activated in rapid response movements.<ref name="Herberholz">{{cite web |last1=Herberholz |first1=Jens |last2=Swierzbinski |first2=Matthew E. |last3=Widjaja |first3=Austin |last4=Kohn |first4=Armand |title=Not so fast: giant interneurons control precise movements of antennal scales during escape behavior of crayfish |url=https://link.springer.com/article/10.1007/s00359-019-01356-y |website=Journal of Comparative Physiology A |access-date=5 January 2024 |pages=687–698 |language=en |doi=10.1007/s00359-019-01356-y |date=1 October 2019}}</ref>

== See also ==
* [[Armour (zoology)]]
* [[Psoriasis]]: a long-lasting autoimmune disease characterized by patches of thin pieces of hard skin like scale.

== References ==
{{reflist}}

== Further reading ==
{{refbegin}}
* {{cite book | last = Kardong | first = Kenneth V. | name-list-style = vanc <!-- | author-link = Kenneth Kardong --> | title = Vertebrates: Comparative Anatomy, Function, Evolution | edition = second | publisher = [[McGraw-Hill]] | year = 1998 | location = USA | pages = 747 | isbn = 978-0-697-28654-3 }}
{{refend}}

[[Category:Animal anatomy]]
[[Category:Marine biology]]
[[Category:Integumentary system]]