zoology Zoology ( , ) is the scientific study of animals. Its studies include the anatomy, structure, embryology, Biological classification, classification, Ethology, habits, and distribution of all animals, both living and extinction, extinct, and ...

, a scale (; ) is a small rigid plate made out of

keratin Keratin () is one of a family of structural fibrous proteins also known as ''scleroproteins''. It is the key structural material making up Scale (anatomy), scales, hair, Nail (anatomy), nails, feathers, horn (anatomy), horns, claws, Hoof, hoove ...

that grows out of

Vertebrate Vertebrates () are animals with a vertebral column (backbone or spine), and a cranium, or skull. The vertebral column surrounds and protects the spinal cord, while the cranium protects the brain. The vertebrates make up the subphylum Vertebra ...

animals Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia (). With few exceptions, animals consume organic material, breathe oxygen, have myocytes and are able to move, can reproduce sexually, and grow from a ...

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 ...

to provide protection. In lepidopterans (

butterflies Butterflies are winged insects from the lepidopteran superfamily Papilionoidea, characterized by large, often brightly coloured wings that often fold together when at rest, and a conspicuous, fluttering flight. The oldest butterfly fossi ...

and

moths Moths are a group of insects that includes all members of the order Lepidoptera that are not butterflies. They were previously classified as suborder Heterocera, but the group is paraphyletic with respect to butterflies (suborder Rhopalocera) a ...

), scales are plates on the surface of the

insect wing Insect wings are adult outgrowths of the insect exoskeleton that enable insect flight, insects to fly. They are found on the second and third Thorax (insect anatomy), thoracic segments (the mesothorax and metathorax), and the two pairs are often ...

, made out of

chitin Chitin (carbon, C8hydrogen, H13oxygen, O5nitrogen, N)n ( ) is a long-chain polymer of N-Acetylglucosamine, ''N''-acetylglucosamine, an amide derivative of glucose. Chitin is the second most abundant polysaccharide in nature (behind only cell ...

instead of keratin, and provide coloration. Scales are quite common and have evolved multiple times through

convergent evolution Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last comm ...

, with varying structure and function. Scales are generally classified as part of an organism's

integumentary system The integumentary system is the set of organs forming the outermost layer of an animal's body. It comprises the skin and its appendages, which act as a physical barrier between the external environment and the internal environment that it serves ...

. There are various types of scales according to the shape and

class Class, Classes, or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytical concept used d ...

of an animal.

Fish scales

Fish scales are dermally derived, specifically in the

mesoderm The mesoderm is the middle layer of the three germ layers that develops during gastrulation in the very early development of the embryo of most animals. The outer layer is the ectoderm, and the inner layer is the endoderm.Langman's Medical ...

. 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. File:Ganoid scales.png, Ganoid scales on a

carboniferous The Carboniferous ( ) is a Geologic time scale, geologic period and System (stratigraphy), system of the Paleozoic era (geology), era that spans 60 million years, from the end of the Devonian Period Ma (million years ago) to the beginning of the ...

fish '' Amblypterus striatus'' File:Denticules cutanés du requin citron Negaprion brevirostris vus au microscope électronique à balayage.jpg, Placoid scales on a

lemon shark The lemon shark (''Negaprion brevirostris'') is a species of shark from the family Requiem shark, Carcharhinidae, known for its yellowish skin, which inspires its common name. It is classified as a Vulnerable species by the International Union for ...

(''Negaprion brevirostris'') File:RutilusRutilusScalesLateralLine.JPG, Cycloid scales on a common roach (''Rutilus rutilus'')

Cosmoid scales

True cosmoid scales can only be found on the

Sarcopterygian Sarcopterygii (; )—sometimes considered synonymous with Crossopterygii ()—is a clade (traditionally a class or subclass) of vertebrate animals which includes a group of bony fish commonly referred to as lobe-finned fish. These vertebrates ar ...

s. The inner layer of the scale is made of lamellar bone. On top of this lies a layer of spongy or

vascular Vascular can refer to: * blood vessels, the vascular system in animals * vascular tissue Vascular tissue is a complex transporting tissue, formed of more than one cell type, found in vascular plants. The primary components of vascular tissue ...

bone and then a layer of dentine-like material called cosmine. The upper surface is

. The coelacanth has modified cosmoid scales that lack cosmine and are thinner than true cosmoid scales.

Ganoid scales

Ganoid scales can be found on gars (family

Lepisosteidae Gars are an ancient group of ray-finned fish in the Family (biology), family Lepisosteidae. They comprise seven living species of fish in two genera that inhabit Fresh water, fresh, Brackish water, brackish, and occasionally marine waters of eas ...

bichir Bichirs and the reedfish comprise Polypteridae , a family (biology), family of archaic Actinopterygii, ray-finned fishes and the only family in the order (biology), order Polypteriformes .Helfman GS, Collette BB, Facey DE, Bowen BW. 2009. The D ...

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. Ganoin scales are diamond shaped, shiny, and hard. Within the ganoin are

guanine Guanine () (symbol G or Gua) is one of the four main nucleotide bases found in the nucleic acids DNA and RNA, the others being adenine, cytosine, and thymine ( uracil in RNA). In DNA, guanine is paired with cytosine. The guanine nucleoside ...

compounds, iridescent derivatives of guanine found in a DNA molecule. The iridescent property of these chemicals provide the ganoin its shine.

Placoid scales

Placoid scale A fish scale is a small rigid plate that grows out of the skin of a fish. The skin of most jawed fishes is covered with these protective scales, which can also provide effective camouflage through the use of reflection and colouration, as w ...

s are found on

cartilaginous fish Chondrichthyes (; ) is a class of jawed fish that contains the cartilaginous fish or chondrichthyans, which all have skeletons primarily composed of cartilage. They can be contrasted with the Osteichthyes or ''bony fish'', which have skeleto ...

including

shark Sharks are a group of elasmobranch cartilaginous fish characterized by a ribless endoskeleton, dermal denticles, five to seven gill slits on each side, and pectoral fins that are not fused to the head. Modern sharks are classified within the ...

s and

stingray Stingrays are a group of sea Batoidea, rays, a type of cartilaginous fish. They are classified in the suborder Myliobatoidei of the order Myliobatiformes and consist of eight families: Hexatrygonidae (sixgill stingray), Plesiobatidae (deepwate ...

s. These scales, also called denticles, are similar in structure to

teeth A tooth (: teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, tear ...

, and have one median spine and two lateral spines. The modern jawed fish ancestors, the jawless ostracoderms and later jawed

placoderm Placoderms (from Ancient Greek πλάξ 'plax'', ''plakos'''Plate (animal anatomy), plate' and δέρμα 'derma'''skin') are vertebrate animals of the class (biology), class Placodermi, an extinct group of prehistoric fish known from Pal ...

s, may have had scales with the properties of both placoid and ganoid scales.

Leptoid scales

Leptoid scales 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. They come in two forms: * Cycloid scales have a smooth outer edge, and are most common on fish with soft fin rays, such as

salmon Salmon (; : salmon) are any of several list of commercially important fish species, commercially important species of euryhaline ray-finned fish from the genera ''Salmo'' and ''Oncorhynchus'' of the family (biology), family Salmonidae, native ...

and

carp The term carp (: carp) is a generic common name for numerous species of freshwater fish from the family (biology), family Cyprinidae, a very large clade of ray-finned fish mostly native to Eurasia. While carp are prized game fish, quarries and a ...

. * Ctenoid scales have a toothed outer edge, and are usually found on fish with spiny fin rays, such as

bass Bass or Basses may refer to: Fish * Bass (fish), various saltwater and freshwater species Wood * Bass or basswood, the wood of the tilia americana tree Music * Bass (sound), describing low-frequency sound or one of several instruments in th ...

and

crappie Crappies () are two species of North American freshwater fish of the genus ''Pomoxis'' in the family Centrarchidae (sunfishes). Both species of crappies are popular game fish among recreational anglers. Etymology The genus name ''Pomoxi ...

Reptilian scales

Gold Dust Day Gecko closeup hawaii edit 1

Reptile Reptiles, as commonly defined, are a group of tetrapods with an ectothermic metabolism and Amniotic egg, amniotic development. Living traditional reptiles comprise four Order (biology), orders: Testudines, Crocodilia, Squamata, and Rhynchocepha ...

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 Crocodilia () is an Order (biology), order of semiaquatic, predatory reptiles that are known as crocodilians. They first appeared during the Late Cretaceous and are the closest living relatives of birds. Crocodilians are a type of crocodylomorp ...

s and turtles, have

osteoderm Osteoderms are bony deposits forming scales, plates, or other structures based in the dermis. Osteoderms are found in many groups of extant and extinct reptiles and amphibians, including lizards, crocodilians, frogs, temnospondyls (extinct amph ...

s underlying the epidermal scale. Such scales are more properly termed

scute A scute () or scutum (Latin: ''scutum''; plural: ''scuta'' "Scutum (shield), shield") is a bony external plate or scale overlaid with horn, as on the shell of a turtle, the skin of crocodilians, and the feet of Bird anatomy#Scales, birds. The ter ...

s. Snakes,

tuatara The tuatara (''Sphenodon punctatus'') is a species of reptile endemic to New Zealand. Despite its close resemblance to lizards, it is actually the only extant member of a distinct lineage, the previously highly diverse order Rhynchocephal ...

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 Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the #Evolutio ...

such as

Carnotaurus ''Carnotaurus'' (; ) is a genus of Theropoda, theropod dinosaur that lived in South America during the Late Cretaceous period, probably sometime between 72 and 69 million years ago. The only species is ''Carnotaurus sastrei''. Known from a si ...

and Brachylophosaurus are known to possess feature scales from skin impressions.

Avian 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 homologous to those of reptiles, but are now agreed to have evolved independently, being degenerate feathers. Carcharodontosaurid theropod dinosaur Concavenator, is known to have possessed these feather-derived tarsal scutes.

Mammalian scales

An example of a scaled mammal is the

pangolin Pangolins, sometimes known as scaly anteaters, are mammals of the order Pholidota (). The one extant family, the Manidae, has three genera: '' Manis'', '' Phataginus'', and '' Smutsia''. ''Manis'' comprises four species found in Asia, while ' ...

. Its scales are made of keratin and are used for protection, similar to an

armadillo Armadillos () are New World placental mammals in the order (biology), order Cingulata. They form part of the superorder Xenarthra, along with the anteaters and sloths. 21 extant species of armadillo have been described, some of which are dis ...

's armor. They have been convergently evolved, being unrelated to mammals' distant reptile-like ancestors (since

therapsids Therapsida is a clade comprising a major group of eupelycosaurian synapsids that includes mammals and their ancestors and close relatives. Many of the traits today seen as unique to mammals had their origin within early therapsids, including li ...

lost scales), except that they use a similar gene. On the other hand, the musky rat-kangaroo has scales on its feet and tail. The precise nature of its purported scales has not been studied in detail, but they appear to be structurally different from pangolin scales. Anomalures also have scales on their tail undersides. 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.

Arthropod scales

Butterflies Butterflies are winged insects from the lepidopteran superfamily Papilionoidea, characterized by large, often brightly coloured wings that often fold together when at rest, and a conspicuous, fluttering flight. The oldest butterfly fossi ...

and

moth Moths are a group of insects that includes all members of the order Lepidoptera that are not Butterfly, butterflies. They were previously classified as suborder Heterocera, but the group is Paraphyly, paraphyletic with respect to butterflies (s ...

s - the order

Lepidoptera Lepidoptera ( ) or lepidopterans is an order (biology), order of winged insects which includes butterflies and moths. About 180,000 species of the Lepidoptera have been described, representing 10% of the total described species of living organ ...

(

Greek Greek may refer to: Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group *Greek language, a branch of the Indo-European language family **Proto-Greek language, the assumed last common ancestor of all kno ...

"scale-winged") - have membranous wings covered in delicate, powdery scales, which are modified

setae In biology, setae (; seta ; ) are any of a number of different bristle- or hair-like structures on living organisms. Animal setae Protostomes Depending partly on their form and function, protostome setae may be called macrotrichia, chaetae ...

. 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 A pigment is a powder used to add or alter color or change visual appearance. Pigments are completely or nearly solubility, insoluble and reactivity (chemistry), chemically unreactive in water or another medium; in contrast, dyes are colored sub ...

ed, but some types of scales are iridescent, without pigments; because the thickness of the platelets is on the same order as the

wavelength In physics and mathematics, wavelength or spatial period of a wave or periodic function is the distance over which the wave's shape repeats. In other words, it is the distance between consecutive corresponding points of the same ''phase (waves ...

visible light Light, visible light, or visible radiation is electromagnetic radiation that can be perceived by the human eye. Visible light spans the visible spectrum and is usually defined as having wavelengths in the range of 400–700 nanometres (nm ...

the plates lead to structural coloration and

iridescence Iridescence (also known as goniochromism) is the phenomenon of certain surfaces that appear gradually to change colour as the angle of view or the angle of illumination changes. Iridescence is caused by wave interference of light in microstru ...

through the physical phenomenon described as thin-film optics. The most common color produced in this fashion is

blue Blue is one of the three primary colours in the RYB color model, RYB colour model (traditional colour theory), as well as in the RGB color model, RGB (additive) colour model. It lies between Violet (color), violet and cyan on the optical spe ...

, such as in the '' Morpho'' butterflies. Some types of

spider Spiders (order (biology), order Araneae) are air-breathing arthropods that have eight limbs, chelicerae with fangs generally able to inject venom, and spinnerets that extrude spider silk, silk. They are the largest order of arachnids and ran ...

s also have scales. Spider scales are flattened setae that overlay the surface of the

cuticle A cuticle (), or cuticula, is any of a variety of tough but flexible, non-mineral outer coverings of an organism, or parts of an organism, that provide protection. Various types of "cuticle" are non- homologous, differing in their origin, structu ...

. 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 spiders (Salticidae) and lynx spiders (Oxyopidae). Some

crustacean Crustaceans (from Latin meaning: "those with shells" or "crusted ones") are invertebrate animals that constitute one group of arthropods that are traditionally a part of the subphylum Crustacea (), a large, diverse group of mainly aquatic arthrop ...

s such as '' Glyptonotus antarcticus'' have knobbly scales. Some

crayfish Crayfish are freshwater crustaceans belonging to the infraorder Astacidea, which also contains lobsters. Taxonomically, they are members of the superfamilies Astacoidea and Parastacoidea. They breathe through feather-like gills. Some spe ...

have been shown to use antennal scales that are activated in rapid response movements.