180 NEBRASKA GEOLOGICAL SURVEY 



generally slim and relatively straight, there are many examples 

 with large dimensions and extreme curvature. The persistence of 

 this vestigial enamel band even in modern elephants is significant. 

 A foot or so may still be seen on young elephant tusks. This is 

 soon worn off by use. Mammoths generally, though not invari- 

 ably, have ponderous tusks distinctly curved and spiral. Those 

 found in this State are noticeably spiral. 



MASTODONS IN GENERAL 



Cope's classification of the mastodons has for a long time made 

 the strongest popular appeal. He divided them into Tetrabelodon, 

 or the four-tuskers, and Dibelodon, or the two-tuskers. This 

 simple division gives the public a clue to the primary divisions 

 of the group. These terms are particularly appropriate and 

 descriptive. 



Mastodons may, in a similar manner, be classed according to 

 the lobes of their teeth, as Trilophodonts (three-crested molars) 

 and Tetralophodonts (four-crested molars). Though serving the 

 purposes of the naturalist, this latter division is less obvious than 

 the former. Both of these general classifications are very useful. 



ELEPHAS 

 (Modern Elephants) 



True Elephants 

 MAMMOTHS 

 (Intermediate Elephants) 



STEGODONS 

 (Intermediate Mammoths) 



MASTODONS } True Mastodons 



(Advanced type) 



\ DIBELODON 



\ (Two-tuskers) 



TETRABELODON 

 (Four-tuskers) 



DlNOTHERIUM. / 



\ PALAEOMASTODON 



\ / 



MOERITHERIUM 



ANCESTRAL 

 PROBOSCIDEAN 



Ancient Mastodons 



