THE CRETACEOUS PERIOD 767 



flightless, highly specialized divers, with aborted wings and remark- 

 able legs. This implies that, following the evolution which had 

 produced the wings, there had been a degenerative history long 

 enough for them to dwindle almost to the point of extinction. Con- 

 current with this, and doubtless its cause, was an extraordinary 

 development of the legs. They were not only very powerful, but 

 the bones of the feet were so joined to the legs as to allow the feet 



Fig. 520. Restoration of the great toothed diver of the Cretaceous, Hes- 

 perornis, by Gleeson, based on a skeleton in the U. S. National Museum. 

 (From Lucas' Animals of the Past; by permission of the Publishers, 

 McClure, Phillips & Co.) 



to turn edgewise in the water when brought forward, thus increasing 

 their efficiency as paddles. Furthermore, the legs were so joined 

 to the body frame as to stand out nearly at right angles to it, like a 

 pair of oars, instead of standing under the body like walking legs. 1 

 Apparently, walking as well as flying had been abandoned, and the 

 organism was specialized for swimming and diving only. For this 

 purpose, the head, neck, and body were admirably adapted. The 

 jaws were armed with teeth set in a groove in primitive saurian 

 fashion, and, like the jaws of snakes, were separable so as to admit 

 1 Lucas, Animals of the Past, 1901, pp. 81-85. 



