The Origins of Avian Plumage

Birds are, monophyletically speaking, the descendant of some of the feathered dinosaurs.

Dinosaurs were (not considering avian descendants) a very particular group of reptiles that descended from common ancestors with modern reptiles, so modern reptiles are not descended from dinosaurs. Only birds are descended from them.

Other non-dinosaur “reptiles” with structures not unlike proto-feathers may have existed. Like the longisquama below.

Or this pterosaur (even though pterosaurs were not dinosaurs), recently found in China, which would show feather-like structures (though not exactly feathers, but pycnofibers).

Feathers, as well as hairs, may have begun to develop from scales (although recently this relationship has been questioned by the modern branch of biology known as Evo-Devo) as early as the Triassic in some archosaurs.

The presence of homologous keratin in both birds and crocodiles indicates that it was inherited from a common ancestor. Which could mean that crocodile scales, bird and dinosaur feathers (as well as pycnofibers of pterosaurs) are all evolutionary expressions of the same primitive skin structures as…