Armour in animals is external or superficial protection against attack by predators, formed as part of the body (rather than the behavioural use of protective external objects), usually through the hardening of body tissues, outgrowths or secretions. It has therefore mostly developed in 'prey' species. Armoured structures are usually composed of hardened mineral

Mineral

A mineral is a naturally occurring solid chemical substance formed through biogeochemical processes, having characteristic chemical composition, highly ordered atomic structure, and specific physical properties. By comparison, a rock is an aggregate of minerals and/or mineraloids and does not...

 deposits, chitin

Chitin

Chitin n is a long-chain polymer of a N-acetylglucosamine, a derivative of glucose, and is found in many places throughout the natural world...

, bone

Bone

Bones are rigid organs that constitute part of the endoskeleton of vertebrates. They support, and protect the various organs of the body, produce red and white blood cells and store minerals. Bone tissue is a type of dense connective tissue...

 or keratin

Keratin

Keratin refers to a family of fibrous structural proteins. Keratin is the key of structural material making up the outer layer of human skin. It is also the key structural component of hair and nails...

.

Armour is evident on numerous animal species from both current and prehistoric times. Dinosaur

Dinosaur

Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...

s such as Ankylosaurus

Ankylosaurus

Ankylosaurus is a genus of ankylosaurid dinosaur, containing one species, A. magniventris...

, as well as other Thyreophora

Thyreophora

The Thyreophora were a subgroup of the ornithischian dinosaurs...

 (armoured dinosaurs such as Ankylosauria

Ankylosauria

Ankylosauria is a group of herbivorous dinosaurs of the order Ornithischia. It includes the great majority of dinosaurs with armor in the form of bony osteoderms. Ankylosaurs were bulky quadrupeds, with short, powerful limbs. They are first known to have appeared in the early Jurassic Period of...

 and Stegosauria

Stegosauria

Known colloquially as stegosaurs, the Stegosauria are a group of herbivorous dinosaurs of the Jurassic and Early Cretaceous Periods, being found mostly in the Northern Hemisphere, predominantly in what is now North America and China....

), grew thick plate-like armour on their bodies as well as offensive armour appendages such as the thagomizer

Thagomizer

Thagomizer is an informal name for the distinctive arrangement of four to ten spikes on the tails of stegosaurid dinosaurs. These spikes are believed to have been a defensive measure against predators.-Paleobiology:...

 or a club

Club (zoology)

In zoology, a club is a bony mass at the end of the tail of some dinosaurs and of some mammals, most notably the ankylosaurids and the glyptodonts...

. The armour took many forms, including osteoderms, spikes, horns and plates. Other dinosaurs such as ceratopsian dinosaurs as well as some sauropods such as Saltasaurus

Saltasaurus

Saltasaurus is a genus of titanosaurid sauropod dinosaur of the Late Cretaceous Period. Relatively small among sauropods, though still massive by the standards of modern creatures, Saltasaurus was characterized by a diplodocid-like head...

 and Agustinia

Agustinia

Agustinia is a genus of sauropod dinosaur from the Early Cretaceous Period of South America. Like all known sauropods, it was quadrupedal and herbivorous. Although some sauropods are known to have body armor, Agustinias armor was unique even among sauropods...

, grew armour to defend themselves, although armour in sauropods overall is uncommon.

In modern times, some molluscs employ the use of shells as armour, and armour is evident in the chitin

Chitin

Chitin n is a long-chain polymer of a N-acetylglucosamine, a derivative of glucose, and is found in many places throughout the natural world...

ous exoskeleton

Exoskeleton

An exoskeleton is the external skeleton that supports and protects an animal's body, in contrast to the internal skeleton of, for example, a human. In popular usage, some of the larger kinds of exoskeletons are known as "shells". Examples of exoskeleton animals include insects such as grasshoppers...

 of arthropod

Arthropod

An arthropod is an invertebrate animal having an exoskeleton , a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...

s. Fish use armour in the form of scales

Scale (zoology)

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...

, whether 'cosmoid', 'ganoid' or 'placoid' and in some cases spines

Spine (zoology)

A spine is a hard, thorny or needle-like structure which occurs on various animals. Animals such as porcupines and sea urchins grow spines as a self-defense mechanism. Spines are often formed of keratin...

, such as on fish such as the stickleback

Stickleback

The Gasterosteidae are a family of fish including the sticklebacks. FishBase currently recognises sixteen species in the family, grouped in five genera. However several of the species have a number of recognised subspecies, and the taxonomy of the family is thought to be in need of revision...

. The chalk

Chalk

Chalk is a soft, white, porous sedimentary rock, a form of limestone composed of the mineral calcite. Calcite is calcium carbonate or CaCO3. It forms under reasonably deep marine conditions from the gradual accumulation of minute calcite plates shed from micro-organisms called coccolithophores....

y plate, or cuttlebone

Cuttlebone

Cuttlebone, also known as cuttlefish bone, is a hard, brittle internal structure found in all members of the family Sepiidae, commonly known as cuttlefish....

, of cuttlefish

Cuttlefish

Cuttlefish are marine animals of the order Sepiida. They belong to the class Cephalopoda . Despite their name, cuttlefish are not fish but molluscs....

 also acts as armour. Most reptile

Reptile

Reptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...

s have scaly skin which protects them from predators in addition to water retention; the crocodile's

Crocodile

A crocodile is any species belonging to the family Crocodylidae . The term can also be used more loosely to include all extant members of the order Crocodilia: i.e...

 exoskeleton

Crocodile exoskeleton

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.-Structure and anatomy:...

 and the shells of the Chelonia - tortoise

Tortoise

Tortoises are a family of land-dwelling reptiles of the order of turtles . Like their marine cousins, the sea turtles, tortoises are shielded from predators by a shell. The top part of the shell is the carapace, the underside is the plastron, and the two are connected by the bridge. The tortoise...

s, turtle

Turtle

Turtles are reptiles of the order Testudines , characterised by a special bony or cartilaginous shell developed from their ribs that acts as a shield...

s and terrapin

Terrapin

A terrapin is a turtle living in fresh or brackish water.Terrapin may also refer to:* Terrapin , a transport vehicle used for amphibious assault by the Allies during the Second World War...

s.

Numerous mammal

Mammal

Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...

s, although not as sturdy as reptilian armour, employ the use of spines and body armour, like the spines of the Echidna

Echidna

Echidnas , also known as spiny anteaters, belong to the family Tachyglossidae in the monotreme order of egg-laying mammals. There are four extant species, which, together with the platypus, are the only surviving members of that order and are the only extant mammals that lay eggs...

 and spiny anteaters and of porcupine

Porcupine

Porcupines are rodents with a coat of sharp spines, or quills, that defend or camouflage them from predators. They are indigenous to the Americas, southern Asia, and Africa. Porcupines are the third largest of the rodents, behind the capybara and the beaver. Most porcupines are about long, with...

s and hedgehog

Hedgehog

A hedgehog is any of the spiny mammals of the subfamily Erinaceinae and the order Erinaceomorpha. There are 17 species of hedgehog in five genera, found through parts of Europe, Asia, Africa, and New Zealand . There are no hedgehogs native to Australia, and no living species native to the Americas...

s. The bony shell of the armadillo

Armadillo

Armadillos are New World placental mammals, known for having a leathery armor shell. Dasypodidae is the only surviving family in the order Cingulata, part of the superorder Xenarthra along with the anteaters and sloths. The word armadillo is Spanish for "little armored one"...

s and the extinct Glyptodon

Glyptodon

Glyptodon was a large, armored mammal of the family Glyptodontidae, a relative of armadillos that lived during the Pleistocene Epoch. It was roughly the same size and weight as a Volkswagen Beetle, though flatter in shape...

 were very much like Ankylosaurus armour and modern armadillos curl up into a ball when threatened, making them unexposed due to their armour. Similarly, the hair

Hair

Hair is a filamentous biomaterial, that grows from follicles found in the dermis. Found exclusively in mammals, hair is one of the defining characteristics of the mammalian class....

y plate-like scales of the pangolin

Pangolin

A pangolin , also scaly anteater or Trenggiling, is a mammal of the order Pholidota. There is only one extant family and one genus of pangolins, comprising eight species. There are also a number of extinct taxa. Pangolins have large keratin scales covering their skin and are the only mammals with...

 are employed in the same way and are constructed of the same material used in the offensive armour, the horn, of the rhinoceros

Rhinoceros

Rhinoceros , also known as rhino, is a group of five extant species of odd-toed ungulates in the family Rhinocerotidae. Two of these species are native to Africa and three to southern Asia....

.

Armour, although all used for the sole intent to ward off attackers, can be split into defensive and offensive armour. Examples of offensive armour are horns

Horn (anatomy)

A horn is a pointed projection of the skin on the head of various animals, consisting of a covering of horn surrounding a core of living bone. True horns are found mainly among the ruminant artiodactyls, in the families Antilocapridae and Bovidae...

, hooves

Hoof

A hoof , plural hooves or hoofs , is the tip of a toe of an ungulate mammal, strengthened by a thick horny covering. The hoof consists of a hard or rubbery sole, and a hard wall formed by a thick nail rolled around the tip of the toe. The weight of the animal is normally borne by both the sole...

, antler

Antler

Antlers are the usually large, branching bony appendages on the heads of most deer species.-Etymology:Antler originally meant the lowest tine, the "brow tine"...

s, claw

Claw

A claw is a curved, pointed appendage, found at the end of a toe or finger in most mammals, birds, and some reptiles. However, the word "claw" is also often used in reference to an invertebrate. Somewhat similar fine hooked structures are found in arthropods such as beetles and spiders, at the end...

s and beak

Beak

The beak, bill or rostrum is an external anatomical structure of birds which is used for eating and for grooming, manipulating objects, killing prey, fighting, probing for food, courtship and feeding young...

s, clubs

Club (zoology)

In zoology, a club is a bony mass at the end of the tail of some dinosaurs and of some mammals, most notably the ankylosaurids and the glyptodonts...

 and pincer

Pincer

Pincer may refer to:*Pincer *Pincer , part of an animal*Pincer ligand, a terdentate, often planar molecule that tightly binds a variety of metal ions.*Pingas...

s, as developed in some mammal

Mammal

Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...

s, bird

Bird

Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...

s, reptile

Reptile

Reptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...

s (including dinosaurs, such as the Dromaeosaurids claw and the Ceratopsian horn) and arthropod

Arthropod

An arthropod is an invertebrate animal having an exoskeleton , a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...

s. Offensive armour is often used in conjunction with defensive armour and in some cases makes an animal almost unassailable.

See also

• Armour (disambiguation)
  Armour (disambiguation)
  - Military and naval :* Armoured forces, heavy cavalry, or tank units—see armoured warfare* Vehicle armour, metal armored to protect fighting vehicles or warships* The metal belt armour, deck armor, turret armor, and command citadel armor of battleship and cruisers...
  
  
• Neck frill
  Neck frill
  Neck frill is the popular term for the relatively extensive margin seen on the back of the heads of reptiles with either a bony support such as those present on the skulls of dinosaurs of the suborder Marginocephalia or a cartilaginous one as in the Frill-necked Lizard...
  
  
• Osteoderms
• Scute
  Scute
  A scute or scutum is a bony external plate or scale, as on the shell of a turtle, the skin of crocodilians, the feet of some birds or the anterior portion of the mesonotum in insects.-Properties:...