132 



EVOLUTION OF MAMMALIAN MOLAR TEETH 



secondarily modified for effective prehension rather than for the fine 

 cutting or mastication of the food, which consists principally of fishes. 

 Here we find the haplodont and triconodont forms secondarily 

 attained. 



Creodonta. In general the earliest or basal Eocene Creodont 

 molars are very important because they present types of upper and 

 lower teeth which are transitional between those of the Insectivora 

 Primitiva, the trigonodont Insectivora, the upper Cretaceous mammals, 



P.! f.J /.# m.i m.z :.J 



.j m.2 m.i p. 4 p. 3 p.2 p.i 



KM;. S4. Typical trituberculatc molars in very primitive Creodonts. Left upper figure, 

 Tricuites eubtrigonus ', right upper figure, Chriucus bntdirini ', central figure, Chriacus truiico.tus ', 

 all Oxyclsenids from the Torrejou Formation, Basal Eocene, Stage II, New Mexico. Lower figure, 

 Triisodon keilprinianus, family Triisodontidrc ('? Mesonychidse), Puerco Formation. Basal Eocene, 

 Stage I, New Mexico. All xi. 



and those of the higher or more specialized Creodonta and Fissipedia. 

 Many early types of molars referred to the Creodonta closely resemble 

 certain molars in the Upper Cretaceous, but the two distinctive 

 features are that they almost invariably present (1) an internal 

 cingulum (wanting in the Upper Cretaceous mammals) and (2) a 

 more or less well developed hypocone rising from this cingulum. 



It was among these Lower Eocene Creodonts that Professor Cope 

 discovered his great generalization as to primitive trituberculy, the 

 upper molars being universally tritubercular, while the lower molars 

 are universally tuberculo-sectorial. 



