Most experts believe that the feathered dinosaurs were warm-blooded and that feathers provided insulation to help keep them warm.  Some dinosaurs had larger feathers than others and they helped them to jump off the ground to grab prey.  Or, they used them glide down from trees and other high places to leap on unsuspecting victims.  Those with the largest and most effective physical characteristics survived while their less fortunate cousins died off.
    The following is a highly condensed version of the theory of feather evolution presented by Dr. Richard O. Prum and Alan H. Brush in the March 2003 edition of Scientific American magazine.  It was included, with their permission, on our Feathered Dinosaur poster.