BIRDS OF THE PAST WETMOEE 385 



in turn is evanescent as the material in wliich it is formed is soft 

 and friable. 



The Miocene of the Sheep Creek and Snake Creek beds of north- 

 western Nebraska under exploration by the American Museum of 

 Natural History, Princeton University, the Carnegie Museum, and 

 Mr. Harold Cook, has yielded a fair number of bones of birds from 

 which 1 have described seven species, including a hawk, Buteo 

 typhoius^ related to the modern red-tail, two small eagles, Geranoaetus 

 ales and G. contortus, of a genus not found outside South America in 

 a living state, and a kite, Proictinia effera. There is also a peculiar 

 limpkin, Aramomis longurio, and a small paroquet, Conuropsis 

 fratercula, allied to the modern Carolina paroquet but smaller. One 

 may picture the area as a badlands section where hawks and eagles, 

 with nest^ on the sides of cliffs, dropped the bones of their prey on the 

 slopes below, to mingle with occasional bodies of the predatory birds 

 that had brought them to the place. 



The Pliocene, like the Oligocene, has fossil birds poorly represented 

 as yet, as at present we know only 10 forms from within the limits of 

 this age. The upper Snake Creek in Nebraska, which is placed in the 

 lower Pliocene, has given u^ an eagle, and a species of chachalaca, 

 Ortalis phengites^ a tree-haunting, gallinaceous type of a group not 

 found to-day north of the lower Rio Grande Valley. From these 

 same deposits I have received the humerus of a crane that is seemingly 

 identical with the existing sandhill crane, the first instance known of 

 remains of a bird still living to be found below the Pleistocene. 

 From beds ascribed to the Upper Pliocene in southern Arizona I have 

 identified a small goose, Bramta mintiscula, a tree duck, Dendrocygna 

 eversa^ a sandpiper, Micropalama hesterwus, and a dove, ChloToenas 

 mAcula. 



Though a part of the birds of the Miocene and Pliocene are 

 peculiar many are identified in genera existing at the present time. 

 It is my own belief that these two ages mark the period of evolu- 

 tion of our modern genera of birds and that there has come com- 

 paratively little change in generic type since. In my opinion evolu- 

 tion among birds during the Quaternary has been concerned prin- 

 cipally with the development of those differences that characterize 

 species and subspecies, differences which in some cases have been 

 so pronounced that present usage, with its close perception of min- 

 utiae, concedes them as generic. When broad, comprehensive limits 

 are given generic groups, however, these seemingly have had their 

 origin in the latter part of the Tertiary. 



It seems probable that the bird life of the Miocene and Pliocene 

 was even more varied and wonderful than that of to-day, and that 

 a larger number of species may have existed. We are told that 

 climatic conditions in that time had not developed such sharply 



