86 ANIMALS OF THE PAST 



change has taken place in them since that 

 time ; they seem to have become so exactly 

 adapted to the conditions of existence that no 

 further modification has taken place. This 

 may be expressed in another way, by saying 

 that while the IVIammals of the Eocene have 

 no near relatives among those now living, 

 entire large groups having passed completely 

 out of existence, the few birds that we know 

 might, so far as their appearance and affinities 

 go, have been killed yesterday. 



Were we to judge of the former abundance 

 of birds by the number we find in a fossil 

 state, we should conclude that in the early 

 days of the world they were remarkably scarce, 

 for bird bones are among the rarest of fossils. 

 But from the high degree of development evi- 

 denced by the few examples that have come 

 to light, and the fact that these represent 

 various and quite distinct species,* we are led 



* Bill three birds, besides a stray feather or l/ro, are so far 

 knotvn from the Eocene of North America. One of these is a 

 fowl not vertf unlike some of the small curassows of South 

 America ; another is a little bird, supposed to be related to the 

 sparrows, while the third is a large bird of uncertain relation- 

 ships. 



