Skin and a Few of Its Derivatives

This chapter deals with amniote skin characters such as scales, feathers, and hair. One of the key novelties of vertebrates is their skin. Vertebrate skin is unique among metazoans in at least two respects. First, vertebrates are the only phylum for which the body is completely covered by a multilayered epidermal cover. Second, the vertebrate skin is a composite structure comprising the epidermis and the dermis. The chapter first examines the developmental evolution of skin and skin appendages in amniotes before discussing mammalian skin derivatives including hairs and breasts. It then considers the evolution of bird skin from scales into feathers and concludes by explaining the origin of feathers.