Part IY. 



SYSTEMATIC SYNOPSIS. 



FOSSIL BIRDS OF NORTH AMERICA, 



There is at present no satisfactory evidence that Birds existed in North America before the 

 Jurassic period ; the footprints in the sandstone of tlie Connecticut Valley attributed to Birds 

 having probably all been made by Dinosaurian Reptiles (p. 63). A number of Cretaceous 

 Birds have been known for S(jme years, sis given in the original edition of this work (1872) ; 

 but it is only since 1881 that this class of vertebrates has been traced back to the Jurassic 

 by the discovery of Laopteryx priscus on a geologic horizon nearly that of the famous 

 ArcluBopteryx. 



The Tertiary Birds of North America belong to genera identical with, or nearly related 

 to, those now living (p. 04). The case i.s otherwise with the earlier forms from the Cretaceous 

 and the Jurassic, which represent diflerent jmrnary divisions of the class Aves (p. 237), com- 

 I>arable in taxonomic value to that one (Saururcc) which is based upon the Archa:optcryx, or 

 to those afforded by the Ratite and the Carinate birds resi)ectively. Most of these forms are 

 Odontornitlics, or Birds with teeth; having the teeth implanted eitlier in grooves {Odon- 

 tolas), or in sockets (Odontotormce), as illustrated by the genera Hesperornis and Ichthyornis 

 respectively. 



In the original edition of the Key these Cretaceous types were ranged with those from the 

 Tertiary, their characters not having been fully worked out at that time. They have since 

 become well known, through Professor Marsh's splendid restorations and illustrations, in his 

 great work entitled ' Odontornithes ' (4to, Washington and New Haven, 1880). 



It is deemed advisable to present the Fossil Birds of North America under the tlirec 

 categories of the Tertiary, the Cretaceous, and the Jurassic forms; the first-named being 

 ranged under the several orders to which they are supposed to belong, as described in this 

 work ; the remainder, with few exce|)tions, being Odontornitl'es. 



