Armour (zoology)

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Armour (or armor) 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 deposits, chitin, bone or keratin.

Examples are:

The shell of various types of mollusc.
The chalky plate (cuttlebone) of cuttlefish.
The chitinous exoskeleton of the arthropods.
The scales on fish, whether 'cosmoid', 'ganoid' or 'placoid'.
The spines on fish, such as the stickleback.
Bony protection, such as in the Thyreophora (armoured dinosaurs such as ankylosauria and stegosauria) and in ceratopsian dinosaurs. This took many forms, including osteoderms, spikes and plates. Even some sauropods had osteoderms e.g. Saltasaurus.
The spines of some dinosaurs (e.g. Agustinia).
The shells of the Chelonia (tortoises, turtles and terrapins).
The Crocodile exoskeleton.
The spines of the Echidna (spiny anteaters) and of porcupines and hedgehogs.
The bony shell of the armadillos and Glyptodon.
The hairy plate-like scales of the pangolin, (constructed similarly to the offensive armour (horn) of the rhinoceros).
Offensive armour, such as horns, hooves, antlers, claws and beaks, clubs and pincers, as developed in some mammals, birds, reptiles (including dinosaurs, such as Dromaeosaurids (claw) and Ceratopsians (horn)) and arthropods.