CENOZOIC ERA: AGE OF MAMMALS 



573 



captured and destroyed by carnivorous mammals. Whatever the 

 cause or causes, the great reptiles — marine, flying, and terrestrial 

 — disappeared; and mammals soon occupied all the places in 

 nature formerly held by them, the only reptiles surviving being 

 those whose habits or inconspicuous form saved them from their 

 competitors. 



The Mesozoic types of birds with toothed jaws and vertebrated 

 tails (p. 560) were replaced by the toothless birds with which we are 

 familiar. 



The difference between the invertebrate life at the close of the 

 Mesozoic and at the beginning of the Tertiary is not great, although 

 the species are different. The most noticeable feature, perhaps, is 

 the absence of an abundant and varied cephalopod fauna which was 

 so conspicuous in the Cretaceous seas. 



Subdivisions of the Cenozoic Era. — The Cenozoic (Greek, kainos, 

 recent, and zoe, life) is the last era in the world's history. It is also 

 called the Age of Mammals because of their predominance and im- 

 portance from the beginning of the era, to, and including the present. 



Cenozoic < 



Quaternary 



Tertiary 



Recent 



Pleistocene (or Glacial) 



Pliocene (Greek, pleion, more, and kainos, recent). More 



than half of the mollusca are living species. 

 Miocene (Greek, melon, less, and kainos, recent). Less than 



half of the mollusca are recent species. 

 Oligocene (Greek, oligos, little, and kainos, recent). Less 



than one fourth of the mollusca are recent. 

 Eocene (Greek, eos, dawn, and kainos, recent). With few 



or no modern species of mollusca. 



This era is separated into two periods, Tertiary and Quaternary, 

 the first lasting until the appearance of the great ice sheets and the 

 second from that time to the present. They were of very unequal 

 duration, the former being several millions of years long, the latter 

 probably less than one million. The life of the Tertiary became more 

 and more modern as the end was approached, and the period is sub- 

 divided into four epochs, as is shown by the above table. In deter- 

 mining the age of the rocks of the Tertiary, however, the percentage 

 of modern species is not computed, but the separation is based on cer- 

 tain species which had a short life and are characteristic of a single 

 epoch. 



