LIFE 565 



at its close, there were some notable deformations in southern 

 Europe. The initiation of the Pyrenees, and of some of the moun- 

 tains farther east, are among the larger disturbances assigned to 

 this time. The greater deformations which expressed themselves in 

 the mountains of Southern Europe were post- Eocene, and most of 

 tin-in considerably later than the close of the Eocene. 



LIFE 



Transition from the Mesozoic. Four salient features marked 

 the transition of life from the Mesozoic to the Cenozoic: (i) among 

 marine animals, nearly all Cretaceous species were replaced by new 

 ones; (2) so many species of land plants lived on as to make it diffi- 

 cult to separate the Mesozoic from the Cenozoic; (3) the great 

 saurians almost disappeared, and most other reptiles showed pro- 

 found changes; and (4) mammals appeared in force, and promptly 

 took a leading place. 



The great change in the epicontinental marine life was due, 

 no doubt, to the withdrawal of the sea from the continent, and the 

 great restriction of the area of shallow water. The increase of the 

 land and the establishment of new land connections may well have 

 caused the existing vegetation to spread and flourish, if the climate 

 remained congenial; but the land faunas did not respond in like 

 manner. 



It is an open question whether the Eocene mammals of North 

 America and Eurasia descended from the primitive types of mam- 

 mals which lived in these continents earlier, or whether they were 

 immigrants. Satisfactory evidence of their descent from the early 

 (non-placental) mammals is wanting, and the suddenness of their 

 appearance in great numbers suggests invasion from some other 

 quarter. The deformative movements which inaugurated the 

 Eocene period quite certainly made new land connections, and fur- 

 nished the conditions for an invasion, if mammals, developed else- 

 where, were awaiting the opportunity. 



Perhaps the rise of mammals caused the downfall of the reptiles. 

 The habit of bringing forth relatively mature offspring, and of nour- 

 ishing and protecting them, gave the mammals an immense advan- 

 tage, to w'lich were added superior agility and higher brain power. 

 It would not be surprising, therefore, if the rise of mammals drove 

 the clumsy, small-brained reptiles either to extinction, or to the 

 assumption of new and smaller forms. 



