THE ALLIES OF THE PIGEON: AVES 397 



last characteristics are strikingly reptilian, and such considera- 

 tions point to the fact that the birds developed from the rep- 

 tiles. As the development was undoubtedly gradual, we should 

 expect to find forms possessing the characters of both groups. 



Many bird-remains have been found, especially in the rocks 

 on the eastern slope of the Rocky Mountains, in Kansas and 

 Colorado, which belong to species which lived later in the 

 period. These birds are of at least two different types, dif- 

 fering in the arrangement of the teeth. One group had the 

 teeth set in separate sockets ; the other had the teeth in 

 grooves. Some of the birds found in the rocks of this age 

 in New Jersey seem to have been toothless, like birds to-day. 

 It is interesting to note that even thus early the bird type 

 had become quite well advanced, having lost not only the 

 teeth but also the long tail of earlier forms. The time of this 

 period was great enough to permit the development of species 

 of birds with highly developed wings, as well as others with 

 degenerate wings. 



In the next succeeding period, to which we shall refer at 

 the close of a later chapter, the birds were all toothless and 

 related to those of to-day. There were woodpeckers, parrots, 

 swallows, cranes, and many others. 



