Variety of animal uses
Keratins are the main constituent of structures that grow from the skin:
- the α-keratins in the hair (including wool), horns, nails, claws and hooves of mammals
- the harder
β-keratins in the scales and claws of reptiles, their shells (chelonia, such as tortoise, turtle, terrapin), and in the feathers, beaks, and claws of birds. These keratins are formed mainly in
beta sheets. However, beta sheets are also found in α-keratins.
Arthropods such as crustaceans often have parts of their exoskeleton made of keratin, sometimes in combination with chitin.
Keratins are also found in the gastrointestinal tracts of many animals, including roundworms (who also have an outer layer made of keratin).
Although it is now difficult to be certain, the scales, claws, some protective armour and the beaks of dinosaurs would, almost certainly, have been composed of a type of keratin.