282 



HISTORICAL PAL.^ONTOLOGY. 



recun^ed, pointed teeth (fig. 212, b). 



grouped together in a new sub-class, 



to7'nitJies or "Toothed Birds." The teeth oi Hesperor7iis (fig. 



212, d) resemble those of Ichthyo7'nis in their general form; 



Hence these forms are 

 , under the name of Odon- 



Fig, 2T2. — Toothed Birds {O do}ito7-7iithes) of the Cretaceous Rocks of America, a. 

 Left lower jaw of Ichthyornis dispar, slightly enlarged ; b. Left lower jaw of Hespej-ornis 

 regalis, reduced to nearly one-fourth of the natural size ; c, Cervical vertebra oi Ichthyomis 

 dispar, front \'iew, twice the natural size ; d. Side view of the same ; d, Tooth of Hesper- 

 omis regalis, enlarged to twice the natural size. (After IMarsh. ) 



but instead of being sunk in distinct sockets, they are simply- 

 implanted in a deep continuous groove in the bony substance 

 of the jaw. The front of the upper jaw does not carry teeth, 

 and was probably encased in a horny beak. The breast-bone 

 is entirely destitute of a central ridge or keel, and the wings 

 are minute and quite rudimentary ; so that Hcsperoniis^ unlike 

 Ichthyo?'?ns, must have been wholly deprived of the power of 

 flight, in this respect approaching the existing Penguins. The 

 tail consists of about twelve vertebrae, of which the last three or 

 four are amalgamated to form a flat terminal mass, there being 

 at the same time clear indications that the tail was capable 

 of up and down movement in a vertical plane, this proba- 

 bly fitting it to serve as a swimming-paddle or rudder. The 

 legs were powerfully constructed, and the feet were adapted to 

 assist the bird in rapid motion through the water. The known 

 remains of Hesperornis 7-egalis prove it to have been a swim- 

 ming and diving bird, of larger dimensions than any of the 



