Los dinosaurios con plumas se consideran formas de transición entre dinosaurios clásicos y aves. Era ya conocido que las aves antiguas como el Archaeopteryx tenían muchas características de reptil, como dientes, y garras en sus dedos, y muchos años antes se había teorizado que los pájaros descendían de dinosaurios terópodos. A finales de los años 1990, los descubrimientos de dinosaurios con plumas en China proporcionaron la prueba concluyente de la conexión, aunque los detalles genealógicos todavía estén siendo dilucidados.Se ha demostrado de muchas formas la relación de descendencia entre aves y dinosaurios, ya que su similitud morfológica en cuanto al cráneo, la cadera, las patas y las extremidades superiores es muy notable. Las aves son claramente monofiléticas y sus primeros representantes se encuentran en el Jurásico (Protoavis, un fósil controvertido de finales del Triásico, es considerado no aviano por la mayoría de los paleontólogos).

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A feathered dinosaur is any species of dinosaur possessing feathers. For over 150 years, since scientific research began on dinosaurs in the early 1800s, dinosaurs were generally believed to be related to the reptile family; the word "dinosaur", coined in 1842 by paleontologist Richard Owen, comes from the Greek for "terrible lizard". This view began to shift during the so-called dinosaur renaissance in scientific research in the late 1960s, and by the mid-1990s significant evidence had emerged that dinosaurs are much more closely related to birds. In fact, birds are now believed to have descended directly from the theropod group of dinosaurs, and are thus classified as dinosaurs themselves, meaning that any modern bird can be considered a feathered dinosaur, since all modern birds possess feathers (with the exception of a few artificially selected chickens). Among extinct dinosaurs, feathers or feather-like integument have been discovered on dozens of genera via both direct and indirect fossil evidence. The vast majority of feather discoveries have been for coelurosaurian theropods. However, integument has also been discovered on at least three ornithischians, raising the likelihood that proto-feathers were also present in earlier dinosaurs, and perhaps even a more ancestral animal, in light of the pycnofibers of pterosaurs. Crocodilians also possess beta keratin very similar to those of birds, which suggests that they evolved from a common ancestral gene.

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