Part IY. 
SYSTEMATIC SYNOPSIS 
OF THE 
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 the Connecticut Valley attributed to Birds 
having probably all been made by Dinosaurian Reptiles (p. 63). A number of Cretaceous 
Birds have been known for some years, as 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 priseus on a geologic horizon nearly that of the famous 
Archceopteryx. 
The "Tertiary Birds of North America belong to genera identical with, or nearly related 
to, those now living (p. 64). The case is otherwise with the earlier forms from the Cretaceous 
and the Jurassic, which represent different primary divisions of the class Aves (p. 237), com- 
parable in taxonomic value to that one (Saururee) which is based upon the Archceopteryx, or 
to those afforded by the Ratite and the Carinate birds respectively. Most of these forms are 
Odontornithes, or Birds with teeth ; having the teeth implanted either in grooves (Odon- 
tolcce), or in sockets {Odontotormcc), 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 three 
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 exceptions, being Odontornithes. 
