STORY TOLD BY FOSSILS 



271 



The rodents? The ungulates? Which group is most useful in your locality? 

 Most harmful? Which members should be destroyed? Protected? 



Self-Testing Exercise 



Mammals are characterized by having (1) blood, 



(2) heart, (3), and a muscular wall just below these organs 



called a (4). Mammals have (5) on the body and 



(6) their young. The important orders are the (7) 



or gnawers, the (8) or hoofed animals, the (9), 



with sharp teeth, and the (10), which includes man. 



PROBLEM X. WHAT STORY IS TOLD BY THE FOSSILS? 



We have learned that animals may be arranged in groups, 

 beginning with very simple one-celled forms and culminating with 

 man himself. These groups are believed by some scientists to rep- 

 resent, in a way, different stages in the evolution or development of 

 life on the earth. 



We know that in the millions of years that life has existed on 

 the earth that there have been many changes. According to present- 

 day evidences, living things at first were very simple in structure, 

 but as time went on more and more complex types appeared. 



Many of you have probably had the interesting experience of 

 finding in rocks, not far from the shore, shells or other evidences 

 of life. Sometimes these were simply 

 casts in rock which once held the 

 remains of animals and plants. In- 

 frequently, we find actual preserved 

 specimens, as insects in amber. All 

 these things are called fossils. If we 

 study the geology of the rocks id 

 which fossils are found, we learn that 

 these rocks were once laid down under 

 water in layers, and that the animal 

 or plant remains were caught there, 



^ & > The Archaeopteryx is the earliest 



then COVered Up, and preserved. We known bird. According to fossil skele- 



i n i xi ±_ j i i j i tons » it was the size of a crow and had 



also find that the rocks nearer the teeth. 



