354 THE BIOLOGY OF BIRDS 



runners, both on the ground and in the trees, but it is not 

 yet clear whether the upright position was first attained upon 

 the ground or in the trees. They very early acquired the 

 habit of perching upright on the branches, as shown by the 

 consolidated instep bones, grasping first digit, and strong 

 claws of Archaeopteryx. Their slender arms ended in three 

 long fingers provided with large claws which were at first 

 doubtless used in climbing. 



*' These active pro-Aves contrasted widely in habits 

 with their sluggish remote reptilian forebears. In pursuit 

 of their prey they jumped lightly from branch to branch and 

 finally from tree to tree, partly sustained by the folds of skin 

 on the arms and legs, and later by the long scale-feathers of 

 the pectoral and pelvic * wings ' and tail. That they held 

 the arms perfectly still throughout the gliding leap still 

 appears doubtful, for no recent animals that do that have 

 attained true flight. I cannot avoid the impression that a 

 vigorous downward flap of the arms, even before they 

 became efficient wings, would assist in the * take-off * for 

 the leap, and that another flap just before landing would 

 check the speed and assist in landing." 



As already indicated, the speculation that most commends 

 itself to us is that birds began as runners and jumpers, that 

 they secondly passed through an arboreal apprenticeship of 

 climbing and volplaning, and that they finally became able 

 to strike the air with wings on which the patagium, still 

 persisting in part, gradually gave place to pinions. 



§ 6. Primitive Toothed Birds 



Archaeopteryx flourished in Jurassic times ; in the next 

 geological period, the Cretaceous, there were primitive 

 toothed birds, the Odontolcae, probably an offshoot from the 

 main Avian stem. The Upper Cretaceous rocks of Kansas 

 have yielded good skeletons of Hesperornis regalis, a flightless 

 aquatic bird, probably related to the modern grebes and 

 divers (Colymbidae). It was about a yard high ; it had 

 rudimentary wings and no keel on the breastbone ; it had 



