BIRDS OF THE PAST WETMORE 381 



on the maxilla alone, the premaxilla being smooth, so that appar- 

 ently even at this remote date there began a tendency to tooth re- 

 duction which has resulted in the toothless jaws found in modern 

 birds. The various species of Hesperoriiis lived in the shallow seas 

 that covered parts of the interior of our country in the Cretaceous, 

 and from their form seem to have fed on fish which they captured 

 by diving. They were so adapted for aquatic life that they had en- 

 tirely lost the power of flight. In fact the wing is known from 

 the humerus alone which is reduced to a slender, curved stylus, the 

 head of which has so slight an articulation on the scapular arch that 

 it is evident that it had little function. It is possible that the remain- 

 ing wing elements were represented by rudimentary bones but these 

 have not been identified, and if present at all they must have been 

 very small. 



Early constructions of the skejeton represented Hesperornis in an 

 upright attitude, but on more careful examination of the articular 

 surfaces of the leg bones it was found that the legs projected at 

 right angles from the body so that it is doubtful if the bird could 

 stand on them at all. It appears that Hesyerornis presented the most 

 highly specialized developments for aquatic life of any bird yet 

 known. It traveled through the water by propulsion of its tremen- 

 dously powerful feet, which are of such form and have such size in 

 relation to the remainder of the skeleton that it is probable that 

 at need the bird could develop the speed and agility in turning found 

 in the modern shark or porpoise. On land, if it ventured at any- 

 time on terra firma, the bird must have progressed like a hair seal, 

 prostrate on the breast; it is possible that it built a nest of floating 

 vegetation in the water like the modern grebes, and seldom if ever 

 did more than flounder out on shore to rest in the sun. If its eggs 

 were placed on shore, we must suppose that they were deposited 

 near the water's edge like those of loons. 



Marsh, deceived by the flat sternum, on which there is no keel 

 for the attachment of flight muscles, characterized Hesperoniis as " a 

 carnivorous, swimming ostrich," while later authors have considered 

 it as perhaps ancestral to the modem grebes and loons. In point 

 of fact Hesperornis is so highly specialized that it is doubtful that 

 it may be considered ancestral to any modern form other than that 

 it represents a type of bird that lived at an earlier age. Resem- 

 bjances to Hesperornis seen in modern species appear to be merely 

 those characterizing birds as a group, or are the preservation in a 

 few of ancient characters which in .the Cretaceous may have been 

 developed in all forms of birds. 



The second type of toothed bird, described from the Cretaceous 

 by Marsh, is Ichthyomis^ a genus in which seven species are at 

 present recognized. Ichthyomis victor (see pi. 5) and /. dispar^ 



