INTRODUCTION . 87 



from among the earth's inhabitants, has thrown a comparatively broad 

 beam of light through the darkness that, broken only by the solitary spark 

 emitted on the recognition of Archceopteryx, had hitherto brooded over our 

 knowledge of the genealogy of Birds, and is even now for the most part 

 palpable. Subsequent visits to the same part of North America, often 

 performed in circumstances of discomfort and occasionally of danger, 

 brought to this intrepid and energetic explorer the reward he had so 

 fully earned. Brief notices of his spoils appeared from time to time in 

 various volumes of the American Journal of Science and Arts (Silliman's), 

 but it is unnecessary here to refer to more than a few of them. In that 

 Journal for May 1872 (ser. 3, iii. p. 360) the remains of a large swimming 

 Bird (nearly 6 feet in length, as afterwards appeared) having some affinity, 

 it was thought, to the Colymbiclse were described under the name of Hesper- 

 ornis regalis, and a few months later (iv. p. 344) a second fossil Bird from 

 the same locality was indicated as Ichthyornis dispar — from the Fish-like, 

 biconcave form of its vertebrfe. Further examination of the enormous 

 collections gathered by the author, and preserved in the Museum of Yale 

 College at New Haven in Connecticut, shewed him that this last Bird, 

 and another to which he gave the name of Apatornis, had possessed 

 well-developed teeth implanted in sockets in both jaws, and induced 

 him to establish for their reception a " Subclass " Odontornithes (page 

 649) and an Order Ichthyornithes. Two years more and the origin- 

 ally found Hesperornis was discovered also to have teeth, but these were 

 inserted in a groove. It was accordingly regarded as the type of a distinct 

 Order Odontolc^ {loc. cit.), to which were assigned as other characters 

 vertebrae of a saddle-shape and not biconcave, a keelless sternum and 

 wings consisting only of the humerus. In 1880 Prof. Marsh brought out 

 a grand volume, Odontornithes, being a monograph of the extinct toothed 

 Birds of North America. Herein remains, attributed to no fewer than a 

 score of species, which were referred to eight different genera, are fully 

 described and sufficiently illustrated, and, instead of the ordinal name 

 Ichthyornithes previously used, that of Odontotorm^ {loc. cit.) was proposed. 

 In the author's concluding summary he remarks on the fact that, while the 

 Odontolcse, as exhibited in Hesperornis, had teeth inserted in a continuous 

 groove — a low and generalized character as shewn by Reptiles, they 

 had, however, the strongly differentiated saddle-shaped vertebras such 

 as all modern Birds possess. On the other hand the Odontotormse, 

 as exemplified in Ichthyornis, having the primitive biconcave vertebrae, 

 yet possessed the highly specialized feature of teeth in distinct sockets. 

 Hesperornis too, with its keelless sternum, had aborted wings but strong 

 legs and feet adapted for swimming, while Ichthyornis had a keeled 

 sternum and powerful wings, but diminutive legs and feet. These and 

 other characters separate the two forms so widely as quite to justify 

 their assignment to distinct Orders, and the opposite nature of the 

 evidence they afford illustrates one fundamental principle of Evolution, 

 namely, that an animal may attain to great development of one set of 

 characters and at the same time retain other features of a low ancestral 

 type. Prof. Marsh states that he had fully satisfied himself that Archse- 

 opteryx belonged to the Odontornithes, which he thought it advisable for 



