BIRDS WITH TEETH. 



27 



SUB-CLASS III. ODOXTOHOLC^E. 



ORDER I. DROMyEOPAPPI. 



Contemporaneous with the Ichthyornis^ other toothed birds of quite different aspect 

 and characters inhabited the same cretaceous sea which then covered the central ami 

 western parts of our continent. The former went hovering over the waters, darting, 

 like the terns and gulls of the present day, upon the unfortunate fishes which cami.> 

 too near the surface ; while the type of the present sub-class, the Hesp&rornis^ or 'the 

 western bird,' as that name literally means, followed the prey to the very bottom of 

 the sea, in diving power and speed surpassing any other bird, living or fossil, and even 

 more fitted for aquatic life than the penguin, as it had no wings whatsoever, and its 

 feet were so specially modified for propelling their large bodies through the water that 

 they could hardly move on land. We will further on have opportunity of characterizing 

 the penguins as the seals among the birds : Hesperornis and its allies represent the 

 dolphins. 



It is most fortunate for science, Professor Marsh remarks, that Hesperornis regaUs 

 with the exception of Archceopteryx and Laopteryx, the oldest bird known should 

 now be represented by remains as complete as any fossil skeleton yet discovered, even 

 in the later formations, as nearly all the bones of the specimens obtained, when first 

 found in the matrix, were almost as perfect as in life ; and the various remains belong- 

 ing to about fifty different individuals of Hesperornis are now in the museum of Yale 

 College. 



With a general superficial resemblance to that of a loon, the skull of Hesperornis, 

 in its more important characters, approaches that of the Struthious birds, being like 

 the latter dromasognathous, and having, like them and IchtJujornis, only one facet on 

 the articular head of the quadrate bone. The nostrils are 

 holorhinal. The brain-case is small, and its sutures entirely 

 fused together. As in Ichthyornis and many recent water- 

 birds, well-marked glandular depressions extend along the roof 

 of the orbits. The premaxillaries were 1 elongated, forming a 

 long, pointed beak, which in front of the nostrils was apparently 

 covered with a horny sheath, as in modern birds. There were 

 no teeth in these bones, as in the upper jaw they were con- 

 fined to the maxillary bones, which were armed with (in II. 

 regalis fourteen) teeth set in a deep, continuous groove, with 

 only faint indications of separate sockets. The lower jaw was 

 thickly set with teeth to the end (in regaUs thirty-three), and 

 the two halves were separate, as in Tchthi/ornis, only united in 

 front by ligament. The teeth, which are so reptilian in their 

 characters that nobody would hesitate to refer them to that 

 class, had they been found alone, were gradually replaced by 

 successional teeth, the germ of the young tooth growing in a 

 pit made in the old one by absorption, thus undermining and 

 at last expelling the latter (Fig. 13). 



In strange contrast to Icht/iyornis, the present group of fossil birds had vertebra? 

 resembling in their more important characters the corresponding vertebras of existing 



Fir,. 1.3. Tooth of Ih-sper- 

 iix, eiil:u'L:<-il: ', germ of 

 second tooth. 



