Last updated
Scutes on an alligator foot Alligator foot detail.jpg
Scutes on an alligator foot

A scute or scutum (Latin scutum, plural: scuta "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 birds. The term is also used to describe the anterior portion of the mesonotum in insects as well as some arachnids (e.g., the family Ixodidae, the scale ticks).



This detail of a Glyptodon displays its scutes. From the collection of the Children's Museum of Indianapolis. The Childrens Museum of Indianapolis - Glyptodon scute - detail.jpg
This detail of a Glyptodon displays its scutes. From the collection of the Children's Museum of Indianapolis.
Detail of scutes of a leopard tortoise Stigmochelys pardalis05.jpg
Detail of scutes of a leopard tortoise

Scutes are similar to scales and serve the same function. Unlike the scales of lizards and snakes, which are formed from the epidermis, scutes are formed in the lower vascular layer of the skin and the epidermal element is only the top surface [ citation needed ]. Forming in the living dermis, the scutes produce a horny outer layer that is superficially similar to that of scales. Scutes will usually not overlap as snake scales (but see the pangolin). The outer keratin layer is shed piecemeal, and not in one continuous layer of skin as seen in snakes or lizards. The dermal base may contain bone and produce dermal armour. Scutes with a bony base are properly called osteoderms . Dermal scutes are also found in the feet of birds and tails of some mammals, and are believed to be the primitive form of dermal armour in reptiles.

The term is also used to describe the heavy armour of the armadillo and the extinct Glyptodon , and is occasionally used as an alternative to scales in describing snakes or certain fishes, such as sturgeons, shad, herring, and menhaden.


The turtle's shell is covered by scutes formed mostly of keratin. They are built similarly to horn, beak, or nail in other species.


The tarsometatarsus and toes of most birds are covered in two types of scales. Large scutes run along the dorsal side of the tarsometatarsus and toes, whereas smaller scutellae run along the sides. Both structures share histochemical homology with reptilian scales, however work on their evolutionary development has revealed that the scales in bird feet have secondarily evolved via suppression of the feather-building genetic program. [1] [2] [3] Unblocking the feather suppression program results in feathers growing in place of scales along the tarsometatarsus and toes. [1] [2] [3] Dinosaur species very close to the origin of birds have been shown to have had "hind wings" made of feathers growing from these areas, suggesting that the acquisition of feathers in dinosaurs was a whole-body event. [3] The bottoms of bird feet are covered in small, keeled scale-like structures known as reticulae. Evolutionary developmental studies on these scale-like structures have revealed that they are composed entirely of alpha keratin (true epidermal scales are composed of a mix of alpha and beta keratin). [3] These data have led some researchers to suggest that reticulae are in fact highly truncated feathers [3] [4]

Insects and other arthropods

The term "scutum" is also used in insect anatomy, as an alternative name for the anterior portion of the mesonotum (and, technically, the metanotum, though rarely applied in that context).

Conspicuous scutum on a typical female hard tick before she has fed. Note the pale eye-spots near the edges of the scutum, roughly between the 2nd and 3rd legs Amblyomma-variegatum-female.jpg
Conspicuous scutum on a typical female hard tick before she has fed. Note the pale eye-spots near the edges of the scutum, roughly between the 2nd and 3rd legs
The same scutum is relatively less conspicuous after the tick has fed, because it has not changed in size, whereas the tick has swollen as it engorged Amblyomma-variegatum-female-engorged.jpg
The same scutum is relatively less conspicuous after the tick has fed, because it has not changed in size, whereas the tick has swollen as it engorged
In the typical male hard tick, the conscutum covers practically the whole back Amblyomma male dorsal.jpg
In the typical male hard tick, the conscutum covers practically the whole back

In the hard ticks, the Ixodidae, the scutum is a rigid, sclerotised plate on the anterior dorsal surface, just posterior to the head. In species with eyes, the eyes are on the surface of the scutum. The flexible exoskeleton posterior to the rigid scutum of the female tick, is called the alloscutum, the region that stretches to accommodate the blood with which the mature female tick becomes engorged. Males do not engorge nearly as drastically as females, so they do not need a flexible alloscutum; instead the rigid scutum covers practically the entire dorsal surface posterior to the head, and may be referred to specifically as the conscutum. [5]

In some species of Opiliones, fused abdominal segments are referred to as a scutum. [6]

See also

Related Research Articles

Scale (anatomy) small rigid plate that grows out of an animals skin

In most biological nomenclature, a scale is a small rigid plate that grows out of an animal's skin to provide protection. In lepidopteran species, scales are plates on the surface of the insect wing, and provide coloration. Scales are quite common and have evolved multiple times through convergent evolution, with varying structure and function.

Claw pointed appendage

A claw is a curved, pointed appendage, found at the end of a toe or finger in most amniotes.

Tick order of arachnids

Ticks (Ixodida) are arachnids, typically 3 to 5 mm long, part of the superorder Parasitiformes. Along with mites, they constitute the subclass Acari. Ticks are external parasites, living by feeding on the blood of mammals, birds, and sometimes reptiles and amphibians. Ticks evolved by the Cretaceous period, the most common form of fossilisation being amber immersion. Ticks are widely distributed around the world, especially in warm, humid climates.

Moulting process by which an animal routinely casts off a part of its body

In biology, moulting, or molting, also known as sloughing, shedding, or in many invertebrates, ecdysis, is the manner in which an animal routinely casts off a part of its body, either at specific times of the year, or at specific points in its life cycle.

Crocodilian armor

The crocodile exoskeleton consists of the protective dermal and epidermal components of the integumentary system in animals of the order Crocodilia. It is a form of armour.

β-keratin or beta-keratin is a member of a structural protein family found in the epidermis of reptiles and birds. β-keratins were named so because they are components of epidermal stratum corneum rich in stacked β pleated sheets, in contrast to alpha-keratins, intermediate-filament proteins also found in stratum corneum and rich in alpha helices. Because the accurate use of the term keratin is limited to the alpha-keratins, the term "beta-keratins" in recent works is replaced by "corneous beta-proteins" or "keratin-associated beta-proteins."

<i>Zuul</i> genus of armored herbivore dinosaurs

Zuul is a genus of herbivorous ankylosaurine dinosaur from the Campanian Judith River Formation of Montana. The type species is Zuul crurivastator. It is known from a complete skull and tail, which represents the first ankylosaurin known from a complete skull and tail club, as well as the most complete ankylosaurid specimen thus far recovered from North America. The specimen also preserved in situ osteoderms, keratin, and skin remains.

<i>Ixodes holocyclus</i> species of arachnid

Ixodes holocyclus, commonly known as the Australian paralysis tick, is one of about 75 species of Australian tick fauna and is considered the most medically important. It can cause paralysis by injecting neurotoxins into its host. It is usually found in a 20-kilometre wide band following the eastern coastline of Australia. Within this range Ixodes holocyclus is the tick most frequently encountered by humans and their pets. As this area also contains the majority of Australia's most densely populated regions, incidents of bites on people, pets and livestock are relatively common.

Ichthyology uses several terms that are unique to the science.

Bird anatomy Physiological structure of birds bodies

Bird anatomy, or the physiological structure of birds' bodies, shows many unique adaptations, mostly aiding flight. Birds have a light skeletal system and light but powerful musculature which, along with circulatory and respiratory systems capable of very high metabolic rates and oxygen supply, permit the bird to fly. The development of a beak has led to evolution of a specially adapted digestive system. These anatomical specializations have earned birds their own class in the vertebrate phylum.

Snake scale Scales which cover the skin of snakes

Snakes, like other reptiles, have skin covered in scales. Snakes are entirely covered with scales or scutes of various shapes and sizes, known as snakeskin as a whole. A scale protects the body of the snake, aids it in locomotion, allows moisture to be retained within, alters the surface characteristics such as roughness to aid in camouflage, and in some cases even aids in prey capture. The simple or complex colouration patterns are a property of the underlying skin, but the folded nature of scaled skin allows bright skin to be concealed between scales then revealed in order to startle predators.

Reptile scale Small rigid plate that grows out of a reptiles skin

Reptile skin is covered with scutes or scales which, along with many other characteristics, distinguish reptiles from animals of other classes. Scales are made of alpha and beta-keratin and are formed from the epidermis. They may be ossified or tubercular, as in the case of lizards, or modified elaborately, as in the case of snakes.

Turtle shell shield for the ventral and dorsal parts of turtles, tortoises and terrapins

The turtle shell is a highly complicated shield for the ventral and dorsal parts of turtles, tortoises and terrapins, completely enclosing all the vital organs of the turtle and in some cases even the head. It is constructed of modified bony elements such as the ribs, parts of the pelvis and other bones found in most reptiles. The bone of the shell consists of both skeletal and dermal bone, showing that the complete enclosure of the shell probably evolved by including dermal armor into the rib cage.

<i>Ixodes pacificus</i> species of arachnid

Ixodes pacificus, the western black-legged tick, is a species of parasitic tick found on the western coast of North America. It is the principal vector of Lyme disease in that region.

Fish scale

A fish scale is a small rigid plate that grows out of the skin of a fish. The skin of most fishes is covered with these protective scales, which can also provide effective camouflage through the use of reflection and colouration, as well as possible hydrodynamic advantages. The term scale derives from the Old French "escale", meaning a shell pod or husk.

Role of skin in locomotion describes how the integumentary system is involved in locomotion. Typically the integumentary system can be thought of as skin, however the integumentary system also includes the segmented exoskeleton in arthropods and feathers of birds. The primary role of the integumentary system is to provide protection for the body. However, the structure of the skin has evolved to aid animals in their different modes of locomotion. Soft bodied animals such as starfish rely on the arrangement of the fibers in their tube feet for movement. Eels, snakes, and fish use their skin like an external tendon to generate the propulsive forces need for undulatory locomotion. Vertebrates that fly, glide, and parachute also have a characteristic fiber arrangements of their flight membranes that allows for the skin to maintain its structural integrity during the stress and strain experienced during flight.

This glossary explains technical terms commonly employed in the description of dinosaur body fossils. Besides dinosaur-specific terms, it covers terms with wider usage, when these are of central importance in the study of dinosaurs or when their discussion in the context of dinosaurs is beneficial. The glossary does not cover ichnological and bone histological terms, nor does it cover measurements.

Plate (anatomy)

A plate in animal anatomy may refer to several things:

<i>Asterolepis</i> (fish)

Asterolepis is an extinct genus of antiarch placoderms from the Devonian of North and South America and Europe. They were heavily armored flat-headed benthic detritivores with distinctive jointed limb-like pectoral fins and hollow spine. The armor plate gives the Asterolepis a box-like shape. Its pectoral fins are also armored but the caudal and dorsal fin are not. The first fossils were named by M. Eichwald in 1840 after noticing star-like markings on the fossils.

Osteoderms are dermal bone structures that support the upper layer of skin and serve as protection against the elements in a large variety of extinct and extant organisms, especially reptiles. This structure is commonly called "dermal armor" and serves to protect the organism, while also helping with temperature regulation. Osteoderms represent hard tissue components of the integument, making them easy to identify in fossil examination. This dermal armor is found prominently in many lizards. Some early amphibians have this armor, but it is lost in modern species with the exception a ventral plate, called the gastralia.


  1. 1 2 Sawyer, R.H., Knapp, L.W. 2003. Avian Skin Development and the Evolutionary Origin of Feathers. J. Exp. Zool (Mol Dev Evol) 298B:57–72.
  2. 1 2 Sawyer, R.H.; Rogers, L.; Washington, L.; Glenn, T.C.; Knapp, L.W. (2005). "Evolutionary Origin of the Feather Epidermis". Dev. Dyn. 232 (2): 256–267. doi:10.1002/dvdy.20291. PMID   15637693.
  3. 1 2 3 4 5 Dhouailly, D (2009). "A new scenario for the evolutionary origin of hair, feather, and avian scales" (PDF). Journal of Anatomy. 214 (4): 587–606. doi:10.1111/j.1469-7580.2008.01041.x. PMC   2736124 . PMID   19422430.
  4. Zheng, X.; Zhou, Z.; Wang, X.; Zhang, F.; Zhang, X.; Wang, Y.; Xu, X. (2013). "Hind wings in basal birds and the evolution of leg feathers". Science. 339 (6125): 1309–1312. CiteSeerX . doi:10.1126/science.1228753. PMID   23493711.
  5. Ivan G. Horak; Heloise Heyne; Roy Williams; G. James Gallivan; Arthur M. Spickett; J. Dürr Bezuidenhout; Agustín Estrada-Peña (14 February 2018). The Ixodid Ticks (Acari: Ixodidae) of Southern Africa. Springer. pp. 46–. ISBN   978-3-319-70642-9.
  6. Ricardo Pinto-da-Rocha; Rafael Fonseca-Ferreira; Maria Bichuette (18 November 2015). "A new highly specialized cave harvestman from Brazil and the first blind species of the genus: Iandumoema smeagol sp. n. (Arachnida, Opiliones, Gonyleptidae)". ZooKeys (537): 79–95. doi:10.3897/zookeys.537.6073. PMC   4714048 . PMID   26798238.