A feathered dinosaur is any species of dinosaur possessing feathers, including all species of birds. In recent decades, evidence has accumulated that many non-avian dinosaur species also possessed feathers or feather-like structures in some shape or form. The extent to which feathers or feather-like structures were present in dinosaurs as a whole is a subject of ongoing debate and research.
It has been suggested that feathers had originally functioned as thermal insulation, as it remains their function in the down feathers of infant birds prior to their eventual modification in birds into structures that support flight.