GEOLOGIC HISTORY OF THE HORSE 



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mammalian life came into existence. All of these changes have 

 taken tens, or more likely hundreds of millions of years, as we can tell 

 from the thickness of the rock deposits in which the fossils are found. 



Amer. Mus. of Nat. Hist. 

 This giant dinosaur, over sixty feet long, lived in Wyoming millions of years ago. 



Other evidences of organic evolution. Evidences of changes 

 in form through past ages have been found in the study of the 

 elephants, which have changed from a trunkless and relatively 

 small animal to the huge elephant of today. The great saber- 

 toothed tiger, which once roamed the fields of California, has 

 given way to the modern type. 



In certain of the higher animals we find traces of organs that 

 are no longer used, although they may have been of value to 

 the animals in the past. The appendix in man is small and use- 

 less, but in some animals, it is large and performs an important 

 digestive function. The muscles of the ears of human beings are 

 useless, but in lower animals they are of great value in aiding the 

 hearing. 



Geologic history of the horse. That developmental changes 

 have taken place in certain types of animals is shown by a study 

 of a series of fossil horse skeletons, which have been reconstructed 

 so that we can pretty certainly tell what ancient horses look like. 



The fossils of leg bones show that, ages ago, the remote ancestors 

 of the horse were probably small animals the size of a domestic 

 cat, with five-toed feet. The earliest horse we have knowledge 



