Feathers are
epidermal growths that form the distinctive outer covering, or
plumage, on
birds and some non-avian
theropod dinosaurs. They are considered the most complex
integumentary structures found in vertebrates, and indeed a premier example of a complex evolutionary novelty. They are among the characteristics that distinguish the extant
Aves from other living groups. Feathers have also been noticed in those
Theropoda which have been termed
feathered dinosaurs.