724 KANSAS CITY REVIEW OF SCIENCE. 



Among existing animals in which the teeth possess short crowns with low 

 blunt tubercles on their triturating face, (the bunodont type of dentition) we ob- 

 serve correspondingly simple digestive apparatus assiciated with a short intestinal 

 canal. In other animals, as many of the existing ungulates for example, the 

 crowns of the teeth are greatly lengthened in a vertical direction, uniformly 

 broadened, and the face presents a complex folding of the enamel plates, (the 

 selenodont type of tooth). Here we notice more complicated digestive organs as- 

 sociated with great length of alimentary tube. The relation of these conditions 

 to the character of the food upon which the respective types subsist is obvious. 

 The Bunodonts require condensed and nutritious diet for their support, and are 

 omnivorous, while the Selenodonts are fitted to subsist upon food containing a 

 smaller proportion of the nutritive elements but of which greater quantity is re- 

 quired. The former are as a general rule dwellers in swamps and forests and 

 live upon nuts, berries, and roots, while the latter occupy the open plains and 

 subsist upon the grasses and branches of trees. Now, any influence sufficiently 

 potent to compel the bunodont ungulates to forsake their natural habitat and live 

 in the open field would also entail corresponding modification or extinction. 

 Such we can easily conceive would be the effects of climatic change or greater 

 incursions from carnivorous enemies. Once in the open field, speed would be- 

 come a desideratum as a condition of safety, hence the foot with a reduced num- 

 ber of digits would possess many advantages over the polydactyle one. Special- 

 ization therefore, I conceive to consist in greater and more perfect adaptation to 

 the conditions under which the animal survives. 



With these facts in view then we may proceed. Prof Cope ventured the 

 assertion some years ago* that the quadritubercular or four-lobed bunodont tooth 

 was the archetypal pattern in which all the more specialized selenodont molars 

 had their origin. This proposition may now be regarded as demonstrated, and 

 the passage from this type of tooth to the highly complicated form in the animals 

 under consideration, I will attempt to show, has been close and consecutive, and 

 intimately associated with reduction in digits. 



As the PhenacodoniidcE, Cope, plainly present us with this hypothetical con- 

 dition both as regards the teeth and the number of digits upon each limb, they 

 cannot be regarded otherwise than as the primitive ancestors of the succeeding 

 members of this important and once populous order. There has been probably 

 no discovery among the ungulates since the finding of the Amblypoda that has 

 proved equal in interest and importance to the discovery of this group. The 

 descent of all the ungulates from the Amblypoda has been held b}^ Prof. Cope for 

 some time, but that this derivation took place from any known genera of this 

 order, the comparatively specialized condition of the teeth of the latter distinctly 

 forbids. This moderate complexity of the teeth among Eocene mammals is a 

 striking exception especially when associated with such a low grade of organiza- 

 tion of other parts as we find in thes6 animals. The explanation of this fact must 



'■■ " On the Origin and Homologies of the Types of Molar Teeth of Mamalia Educabilia." Jour. Acad. 

 Sci., Philadelphia, 1874. 



