Prehistoric birds\' wings were much more primitive than today, with rigid layers of feathers acting as simple airfoils for gliding, British researchers say. Scientists at the University of Bristol, with American and Canadian colleagues, said although feathers eventually led to the evolution of flight, they first appeared in dinosaurs for much different purposes. Close examination of the earliest theropod dinosaurs suggests feathers were initially for insulation, arranged in multiple layers to preserve heat, before their shape evolved for display and camouflage, a Bristol release said Thursday. \"We are starting to get an intricate picture of how feathers and birds evolved from within the dinosaurs,\" Bristol researcher Jakob Vinther said. \"We now seem to see that feathers evolved initially for insulation. Later in evolution, more complex vaned or pinnate feathers evolved for display.\" As evolution changed the configuration of the feathers, their important role in the aerodynamics and mechanics of flight began to emerge, the researchers said. \"These display feathers turned out to be excellent membranes that could have been utilized for aerial locomotion, which only very late in bird evolution became what we consider flapping flight,\" Vinther said. \"This new research is shedding light not just on how birds came to fly, but more specifically on how feathers came to be the way they are today -- one of the most amazing and highly specialized structures in nature.\" Millions of years of evolution modified dinosaurs\' forelimbs into highly efficient, feathered wings that could rapidly change their span, shape and area, allowing dinosaurs to take to the skies, the researchers said.