62 ANIMALS OF THE PAST 



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 con- 

 clude that in the early days of the world they were re- 

 markably 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 to conclude that birds were 

 abundant enough, but that we simply do not find them. 



Several eggs, too — or, rather, casts of eggs — ^have 

 lately been found in the Cretaceous and Miocene strata 

 of the West; and, as eggs and birds are usually asso- 

 ciated, we are liable at any time to come upon the bones 

 of the birds that laid them. 



To the writer's mind no thoroughly satisfactory ex- 

 planation has been given for the scarcity of bird re- 

 mains; but the reason commonly advanced is that, 

 owing to their lightness, dead birds float for a much 

 longer time than other animals, and hence are more 

 exposed to the ravages of the weather and the attacks of 

 carrion-feeding animals. It has also been said that the 

 power of flight enabled birds to escape calamities that 

 caused the death of contemporary animals; but aU 

 birds do not fly; and birds do fall victims to storms, 

 cold, and starvation, and even perish of pestilence, like 

 the Cormorants of Bering Island, whose ranks have 

 twice been decimated by disease. 



'But three birds, besides a stray feather or two, are so far known from 

 the Eocene of North America. One of these is a fowl not very unlike 

 some of the small cm-assows of South America; another is a little bird, 

 supposed to be related to the sparrows, while the third is a large bird of 

 uncertain relationships figured in the chapter on feathered giants. 



