THE HISTORY OF ANIMAL LIFE 



397 



extinct animals; paleobotany with extinct plants. The facts that 

 have been revealed by such studies have aided greatly in arranging 

 present-day animals and plants in their proper taxonomic rela- 

 tionships. 



E/fAS 



CCNOZOIC 



MO/fC THAN 

 l/! MILUOH 

 CCNTURICS 



MESOZOIC 



ncahly 

 i uillion 



CCNTVIieS 



PALEOZOIC 



I MILLION 

 CtNTUKICS 



f-noTERozoic 



10 MILLION 

 CfNTUBICi 



ARCHEOZOIC 



to MILLION 



cenTu/fics 



PERIODS 



QUATERNARy 



TERTIARY 



CRETACEOUS 



JURASSIC 



TRIASSIC 



PERMIAN 



CARBONirEROUS 



DEVONIAN 



SILURIAN 



ORDOVICIAN 



CAMBRIAN 



APTHROPODA 



CHORDATA 



Fig. 221. — Table of the geological eras and representative animal types. 



Representatives of all existing orders of animals are found among 

 fossils, and in addition a considerable number of other orders that 

 have become extinct. Thus our present-day forms represent only a 

 portion of the number of types that have appeared. For convenience 



