Feathers continue to define birds. They are the only living animals that have feathers, and all birds have some type of feathers. Feathers result from a modification of the outer layer of the bird’s skin, the epidermis, and probably evolved from scales as found on reptiles, such as snakes and lizards. They are composed largely of keratin, an inert substance that is light, strong, and long-lasting. While a bird is still developing inside its egg, it is covered with bumps called papillae, and... więcej
Salem Press Encyclopedia of Science, 2020. 2p.