GENERAL ZOOLOGY 



Fig. 18.26. Ancient and modern 

 birds completely adapted to aquatic 

 ife. A, restoration of Hesperornis, a 

 ie;htless diving bird which inhabited 

 the shallow sea that covered what is 

 now Kansas during the Cretaceous 

 period. B, King penguins, Aplenodytes 

 pataoomca, with wings reduced and 

 modified to form swimming paddles. 

 (A, redrawn from G. Heilmann, The 

 Onain of Birds, copyright 1927 by 

 D. Appleton and Co., printed bv 

 permission of Appleton-Centurv- 

 Crofts, Inc.; B. photograph courtesy 

 New York Zoological Society. 



the great majority of birds whicii are adapted for flight. The flying birds 

 typicafly have a keeled sternum for attachment of the powerful wing muscles, 

 whereas in the cursorial or running birds the wings and flight muscles are 

 much reduced and the sternum is without a pronounced keel. 



The poverty of the fossil record of birds seems explicable by the fact that a 

 bird, with its light body, particularly its light bones, is much less likely to 



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