^46 The Earth and Its Inhabitants Change unit x 



continuing the same column, list in order, beginning again with the 

 simplest, the classes of vertebrates. Next to each phylum and class show 

 in which era the form first lived in large numbers, judging from fossils 

 found. What interesting fact, if any, do you note? 



5. The recent sedimentary rocks of Wyoming and Montana have re- 

 mained comparatively undisturbed throughout the ages. How did this 

 affect the work of building up the fossil series of the horse? 



Further Activities in Biology 



1. Make models of prehistoric forms. You could use plasticine or soap. 



2. If you can draw, you can make very interesting drawings of some 

 of the scenes in earth history. Of course, you will have to do some read- 

 ing first to be sure that you have correct information. Perhaps a friend 

 could help you do some of the research. A mural showing the stages in 

 earth history would be suitable for the halls or library. 



3. The "tree of life" has been drawn in several ways by biologists. Ex- 

 amine zoology and botany books to see whether you can find some. Ex- 

 plain them to the class. Sometimes there is fossil evidence that the de- 

 scendants of a form changed in two directions, some giving rise to one 

 kind of organism, others to another type. Can vou show this in a tree 

 diagram? 



4. A series of drawings showing the development of plants tlii^ough 

 the ages would be interesting. 



5. What kind of evidence has convinced biologists that birds came 

 from a reptilelike organism? Present it to the class for discussion. 



