I'ALEONrOLOaV 



333 



One can but conjecture the factors responsible for the demise of the 

 offshoots of the family tree of the horse; for the loss of the collateral 

 lines among the elephant's kindred; for the failure of the ammonites in 



Fig. 228. — Skeleton of a Permo-Carboniferous reptile, Edaphosaurus cruciger. (From 

 a specimen in the Museum of Geology, University of Michigan, mounted under the direction of 

 Professor E.. C. Case.) 



the cephalopods' struggle for existence; and for the extinction of the 

 reptilian aristocracy, the dinosaurs. Many surmises have been offered. 

 Most suggestions are to the effect that these animals found themselves 





J '/■'./■ 





- A^Jt^ 



Fig. 229. — Restoration of the reptile Edaphosaurus cruciger. (By Professor E. C. Case.) 



in an unsuitable environment and that the environment became inhospi- 

 table through geological or climatic changes or through the rise of other 

 (inimical) forms of Hfe. However, it is quite possible that any lack of 



