EOCENE 503 



(PI. XI, Figs. 2, 3) and Gastropods (XI, 4, 5) increase greatly and 

 are very rich in species. Nautiloid Cephalopods are more varied 

 and widely distributed than now (XI, 8), and in a few localities 

 Ammonites and Belemnites have been found, but these are mere 

 belated stragglers from the Cretaceous and are much too rare to 

 be at all characteristic. Among the Crustacea should be noted 

 the great increase of the Crabs, which are even more numerous 

 and varied than in the Cretaceous. 



The Fishes, both fresh-water and marine, differ only in minor 

 details from modern fishes. The Reptiles are likewise essentially 

 modern in character, and only two groups, the Lizards and Snakes, 

 are more numerous than they had been in Mesozoic times, though 

 the venomous snakes had not yet appeared. The Eocene lakes 

 of the West contained multitudes of large Crocodiles and a great 

 variety of Turtles. 



Eocene Birds are very much more numerous, advanced, and 

 diversified than those of the Cretaceous ; one characteristic feature 

 of the times was the presence in Europe and America of extremely 

 large, flightless birds, more or less like the ostriches in appearance. 

 Of flying birds there were many kinds ; Owls, Eagles, Buzzards, 

 Vultures, Gulls, Waders, Woodcock, Quail, Ibis, and Pelicans are 

 represented by ancestral forms, somewhat different from their 

 modern descendants. 



The Mammals have developed in a marvellous way since the 

 Cretaceous, assuming in terrestrial life that dominant place which 

 they have ever since held. Compared with the evolution of other 

 animal groups, that of the mammals has been so rapid that each 

 stage of the Eocene has its. own mammalian fauna, differing from 

 those of the preceding and succeeding stages. Besides these 

 geological differences between the successive mammalian assem- 

 blages, there are often marked geographical differences between 

 the faunas which are of approximately contemporaneous age, 

 but widely separated in space. Comparing Europe and North 

 America in this respect, we find that in the Eocene each con- 

 tinent had its own peculiarities, but that the land connection be- 

 tween them allowed continual intermigration and thus kept up 



