ORDINAL TYI'KS OF MOLAKS: ARTIODACTYLA 



171 



ARTIODACTYLA. 



Of this even-toed group of hoofi.-d mammals the must ancient 

 representative is found in the lower Eocene or \Yasatdi lieds. It is 



eft me p 



en" me" pa" 



hf /;/ 



A hf pr< 



hl j en" me" Da" en" me" 



Fi<;. 152. Lower teeth of 2Y,>/,!../ ( ^..< a very primitive Artiodactyl from the \Vasatch Forma- 

 tion, Lower Eocene. 



A. Triiivnolestes c/tc.censis, paraconid small but distinct. X-3-. B. TI-'J<>, //<.</, s metsiocus, 

 paraconid reduced. x|-. C. Ti'i'.iv<i<>l<.!ttis ttmt</irns, parauonid vestigial or absent, all cusps low 

 and rounded. xA. 





Fn;. 1S3. A quudritubercular to bilophodoiit Peccary, P/<iti/.i<,ntix l>~,cul,-n ,;,1 ,< x . family Dicoty- 

 lida?, from the Blanco Beds, Pliocene, of Texas, x^. After Gidley. The incipient bilophodont 

 condition* is seen in Dicoiyti-x and even among Baboons (r//,. 



the little species Trigonolestes c/iacciiftis (Fig. 152) of the Wasatch, which 

 is undouhtedly an Artiodactyl, as shown by the associated astragalus. 



* [The more or less completely bilophodont type has been secondarily developed 

 independently in many other families. Among Artiodactyla we also have Lixtriodon 

 (SuicUe), Tapirnlus (Anoplotheriidae) ; among Perissodactyls, the Tapirida?, not to mention 

 the early Equida- and the RhinocerotidaB, Lophiodontidse in which the anterior and posterior 

 crests are connected by the high external cusps or ci-est. Among the Proboscidea we have 

 especially Uinotheriidtw and Palceomastodon ; among Pyrotheria, Pyrotlierium ; in certain 

 other Ungulates, e.r/. Uintatherium, Arsinoitherium, the bilophodonty is 7iot strictly typical. 

 Among Sirenia we have Manatux ; among Marsupials, the Kangaroo and Diprotodon. Even 

 certain Theriodont reptiles (Trirachodon) developed a transverse crest in each molar 

 and the whole series of cheek teeth was thus functionally analogous to a bilophodont 

 dentition. ED.] 



