EVOLUTION OF THE VERTEBRATES 



155 



through extension of the scales, and the use of these broadened 

 limbs as aids to locomotion. Many birds now flap their wings 

 for this purpose while running. Such primitive wings would also 

 have been of aid in jumping from branch to branch or from tree 





Coracold ■ 

 Humerus 



• Furcula, ; ; 



^r4^-'^^, ;; /m 



' ' It 





Radius 



Fig. 86. — Archaeopteryx lithographica, as it appeared in the fossil specimen. 

 I-IV, digits. (From Hegner after Steinmann and Doderlein.) 



to tree, or in sailing out over the water to dive for fish. None of 

 the theories has any particular advantage over the others, although 

 the one fossil pro-avian, Archaeopteryx, was probably a climber. 

 However, this may indicate either that it climbed trees or that it 



