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Armor orarmour inanimals is a rigidcuticle orexoskeleton that provides exterior protection against attack bypredators,[1] formed as part of the body (rather than the behavioural utilization of external objects for protection) usually through the thickening and hardening of superficialtissues, outgrowths orskinsecretions. It is often found inprey species that are too slow or clumsy to outrun predators,[2] or those that would stand their ground and fight, thus needing to protectvital organs againstclaw,talon orbite injuries.
Armoured structures are usually composed of hardenedmineral deposits,chitin,bone, orkeratin.
Armour is evident in numerous animal species from both current and prehistoric times.Dinosaurs such asAnkylosaurus, as well as otherThyreophora (armoured dinosaurs such asAnkylosauria andStegosauria), grew thickplate-like armour on their bodies as well as offensive armour appendages such as thethagomizer or atail club. The armour took many forms, includingosteoderms, spikes, horns, and plates. Other dinosaurs such asceratopsian dinosaurs as well as somesauropods such asSaltasaurus, grew armour to defend themselves, although armour in sauropods overall is uncommon.
In modern times, somemolluscs employ the use ofshells as armour, and armour is evident in thechitinousexoskeleton of arthropods. Fish use armour in the form ofscales, whether 'cosmoid', 'ganoid' or 'placoid' and in some casesspines, such as on fish such as thestickleback. Thechalky plate, orcuttlebone, ofcuttlefish also acts as armour. Mostreptiles havescaly skin which protects them from predators in addition to water retention; thecrocodile'sscutes and the shells of theChelonia:tortoises,turtles andterrapins.
Numerousmammals employ the use of spines and body armour, although not as sturdy as reptilian armour, like the spines of theechidnas and ofporcupines andhedgehogs. The bony shell of thearmadillos and the extinctGlyptodon were very much likeAnkylosaurus' armour and some modern armadillos curl up into a ball when threatened, making them unexposed due to their armour. Similarly, thehairy plate-like scales of thepangolin are employed in the same way and are constructed of the same material used in the offensive armour, the horn, of therhinoceros.
Armour, although all used for the sole intent to ward off attackers, can be split into defensive and offensive armour. Examples of offensive armour arehorns,hooves,antlers,claws,beaks,clubs andpincers, as developed in somemammals,birds,reptiles (including dinosaurs, such as thedromaeosaurid claw and theceratopsian horn) andarthropods. Offensive armour is often used in conjunction with defensive armour and in some cases makes an animal almost unassailable.