Editing Scale (zoology) (section)

==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]].