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Feather Evolution

    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.

Protofeathers
   Feather growth began with a thickening of the epidermis (skin), which elongated into a hollow tapered tube. These tubes became "protofeathers."  They have been found on the  primitive compsognatids, such as Sinosauropteryx.
 
Barbed Ridge
   There are two possibilities regarding what occurred next.  The first is that a second layer evolved that created a follicle collar. The inner layer became a barbed ridge and the outer later evolved into a protective sheath.
Stem Evolution
   It is also possible that the rachis, or stem, was the first to evolve and a large number of barbs radiated outward from it.
Barbules introduced
   Although this looks similar to the barbed ridge shown above, a close examination reveals that he barbs have developed very tiny branches called barbules. These feathers appear fuzzy or downy.
Complete Feather
   Regards of which of the two features came first, their evolution resulted in the first double-branched feather having rachises, bars and barbules.  The bars and barbules formed a tight weave, resulting in an almost solid surface. 
Flight Feather
  Unlike the first complete feathers, flight feathers were asymmetrical (one side wider than the other).  This made flight possible.  Such feathers have been found on all of the prehistoric birds and are found on modern birds.

 


 

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