Feathers, both down-like and vaned, are clearly present on the body, arms, legs and tail. Protoarchaeopteryx , in particular, has vaned, barbed feathers protruding from the end of its tail in a fanlike pattern. In all other respects both specimens are certainly dinosaurs, so the presence of feathers can no longer be an exclusive hallmark of birds. The feathers of both fossils are long and contain a central shaft. In both instances the vanes are symmetrical, whereas those of most flying birds, even Archaeopteryx , are asymmetrical.
Asymmetrical vanes provide the lift required for flight.
This coupled with the fact that the arms of both fossils are barely two-thirds as long as the legs, makes it highly unlikely that these animals could fly. The presence of feathers on ground-dwelling, flightless theropods suggests that feathers were fully formed before flight had been achieved. Various ideas include insulation, camouflage, mating display and species recognition. Flight, it seems, was not what feathers were originally for and uncoupling feathers from flight fits in with the way many evolution biologists believe feathers evolved. They have long insisted that feathers could not have arisen fully formed and capable of flight, but evolved from intermediate structures that had to provide some advantage to the bearer other than flight in order to be favored by natural selection.