272 



HOW DO WE CLASSIFY ANIMALS? 



surface contain remains of living things that inhabited the earth in 

 fairly recent time, while those deeper in the earth contain fossils 

 of animals and plants that are unlike any that are now living, 

 and are, therefore, thought to have lived millions of years ago. 

 In this way scientists have learned that the earliest forms of life 

 upon the earth were very simple, and that gradually more and 

 more complex forms appeared, as the rocks formed latest in 

 time show the most highly developed forms of plant and animal 

 life. 



Some evidences of ancient forms of life. From a study of 

 fossils from various rock formations all over the world the following 

 very interesting facts have been discovered : that the oldest rocks 



contain very simple 

 plants and animals, al- 

 most all marine ; that 

 there came a period in 

 which many kinds of 

 invertebrates lived, at 

 this time land plants 

 appeared ; then came 

 the age of fishes, many 

 of which were great 

 armored beasts, long 

 since gone. Still later 

 we have an age of am- 

 phibians. During this 

 last period great forests 

 flourished from which 

 our anthracite coal beds 

 were formed. Then 

 came a time when mon- 

 strous reptiles roamed 

 over the earth, some 

 of them 60 to 70 feet 

 in length. Later these 

 great animals, dinosaurs, vanished and huge batlike animals and 

 birds appeared. During this time the beginnings of our modern 



Alma Chesnut — Amer. Nature Ass' 



Unearthing the bones of huge animals which at one 

 time lived in Wyoming. These bones are relics of a 

 mighty race that perished in forgotten ages. 



