Feather is the best-defined trait of birds. For a long time, it was thought that feather coevolved with the evolution of birds, but recent discoveries have challenged this view. It now seems likely that feathers were in fact shared across many, if not all dinosaurs. Recent discoveries of feathers in pterosaurs, probably homological to those of birds, extends this view even further to the ancestor of Avemetatarsalia. This makes it possible to reconstruct a more exhaustive phylogenetic tree of the evolution of the feather according to different feather types that haven’t been found in modern bird species. The research is complemented by studies in developmental biology of feathers and other integumentary structures present in vertebrates such as scales, hairs and odontodes. This makes a foundation for an early origin of feathers hypothesis that puts their emergence at the time of recovery from the End-Permian mass extinction event. It seems likely that, initially, feathers served a function of insulation and signaling and thus provided their carriers with an evolutionary edge against other competitive groups of that period such as synapsids and other Archosarus.