RESTORATION OF HESPERORNIS. 113 



reptiles, in form, structure, and succession, is evidence of this, and their 

 method of implantation in a common alveolar groove (Holcodont), con- 

 forms strictly to what we have in one well known group of reptiles, exem- 

 plified by Ichthyosaurus. This method of insertion in the jaw is a primitive 

 dental character, quite different from what we should naturally expect as 

 an accompaniment of the modern style of vertebra, and is a much lower 

 grade than the implantation of the teeth in distinct sockets (Thecodont), 

 a feature characteristic, as we shall see, of another group of Odontomithes, 

 of which Ichthyornis is the type. These teeth indicate unmistakably that 

 Hesperornis was carnivorous in habit, and doubtless was descended from 

 a long line of rapacious ancestors. 



In considering the limbs of Hesperornis, two explanations of their 

 pecidiar modifications naturally suggest themselves. The rudimentary 

 wings, viewed in the light of modem science, clearly indicate that 

 Hesperornis was in this respect a degraded type. The Struthious characters 

 which we have noticed in various parts of the skeleton might be regarded, 

 not as evidence of close relationship, but rather as general reptilian 

 characters, common to the two groups through inheritance from a remote 

 reptilian ancestry. According to this view, the wings may have been 

 gradually lost by disuse, after the aquatic life was assumed. In proportion 

 as the wings diminished, the legs and feet increased in size, for then* 

 work increased. This change would be strictly in accordance with the 

 law of compensation, and the well known economy of nature. 



We may suppose, moreover, the ancestors of Hesperornis to have been 

 at one time on an equality with the Loon, and later with the Penguin, in 

 respect to means of flight and swimming. As the wings slowly diminished 

 in size, first came the loss of flight, while the wings retained, doubtless for 

 a long time, their power of propulsion through the water. As this too 

 became gradually restricted, the legs and feet gained proportionally. The 

 power derived from them, aided indirectly by the tail, in time so predom- 

 inated, that the wings became entirely aborted, a remnant of the humerus 

 alone remaining. 



15 



