4 The Bird 



session of low islands which marked the position of the 

 present Rocky Mountains. In the shallow tropical sea, 

 •extending from this land five hundred miles or more to 

 the eastward, and to unknown limits north and south, 

 there was the greatest abundance and variety of fishes, 

 and these doubtless constituted the main food of the 

 present species. Hesperornis, as we have seen, was an 

 admirable diver ; while the long neck, with its capabilities 

 of rapid flexure, and the long slender jaws armed with 

 sharp recurved teeth, formed together a perfect instru- 

 ment for the capture and retention of the most agile fish. 

 The lower jaws were united in front only by cartilage, 

 as in serpents, and had on each side a joint which admitted 

 of some motion, so the power of swallowing was doubt- 

 less equal to almost any emergency." 



Hesperornis had numerous teeth set in grooves like 

 those of serpents and crocodiles, but in Ichthyornis ('Fish- 

 bird,' so called because its vertebrae are biconcave like 

 those of a fish) the teeth were in separate sockets as in 

 alligators. The latter bird was not large, being about 

 the size of a pigeon, and it had well-developed wings. 



It is interesting to compare Hesperornis with the 

 ^roup of penguins, both being highly specialized, although 

 in ways so different, for an almost wholly aquatic life. 

 Hesperornis swam by strong strokes of its great webbed, 

 or lobed, toes, its wings dangling uselessly for genera- 

 tion after generation, until all trace, save a vestigial 

 Iiumerus, of their bony support disappeared. Penguins-, 

 however, make but little use of their feet in swimming, 

 only occasionally aiding the tail in steering; but they 



