You see them on bird and chickens. Feathers are epidermal growths that make animals from the Class Aves distinct from other animal classes. They are formed from a controlled production of epidermal cells producing keratin proteins. Feathers are complex organ structures that help protect and cover birds.

There are different types of keratin. Alpha keratins are strong components of the hoofs, horn, and hair of mammals. Beta keratins, on the other hand, are much stronger than alpha keratins. Beta keratins are made up of hydrogen-bonded protein strands resulting in beta-pleated sheets. These sheaths are then cross-linked and twisted into structures like beaks, claws and feathers by disulfide bridges.