CHAPTER XVII. 



CONCLUSION. 



Havixg now described the more important characters in the structure, 

 so far as known, of the two groups of Cretaceous Oclontomitlies, or Birds 

 with teeth, it remains to consider what relation these birds bear to each 

 other, and to allied members of the class; and, also, to inquire if the 

 facts presented throw any light on the profounder question as to the origin 

 of Birds. 



In comparing Hesperornis and Ichthyornis, as the types of their 

 respective orders, the Odontolcce and Odontotomies, the contrast in then- 

 principal characters is as striking as it is unexpected. Hesperornis had 

 teeth implanted in a continuous groove, a low, generalized character ; 

 with, however, the strongly differentiated saddle-shaped vertebrae. Ichthy- 

 ornis, on the other hand, had the primitive biconcave vertebras, and 

 vet the highly specialized feature of teeth in distinct sockets. Better 

 examples than these could hardly be found to illustrate one fact brought 

 out by modern science, that an animal may attain great development in 

 one set of characters, and at the same time retain other low features of the 

 ancestral type. This is a fundamental principle of evolution. 



The more superficial characters of the absence of wings and the 

 strong swimming legs and feet of Hesperornis are in striking contrast, also, 

 with the powerful wings and diminutive legs and feet of Ichthyornis. 

 These and other characters, already mentioned, separate the two birds 

 so widely that a more detailed comparison seems here unnecessary. 



