1010.] Characters of the Stem Perissodactyls. 380 



Dental formula: Ixlx Preserved in most Lower Eocene Perissodaetyls. 

 Taken in connection with the form of the teeth and many other characters 

 it is a significant indication of derivation from the stock which gave rise 

 also to the Insectivores, Creodonts and Condylarths. 



Canine stout, piercing; incisors in a transverse or partly elongate row: 

 crowns convex anteriorly, flattened posteriorly. Indicates derivation from 

 omnivorous Creodont Condylarths; canines possibly preserved as fighting 

 weapons. 



Premolars similar to the Euprofogonia type, namely: p* triangular; with 

 proto-, deutero- and tritocones, protoconule, metaconule and strong sur- 

 rounding cingula; })•' simpler, p- compressed, p^ conic. 



Upper molars similar to the Euprotogonia type but protoconule and 

 metaconule becoming lophoid, paracone and metacone rounded {of. Hyra- 

 cotherium leporinum) . 



Lower cheek teeth much as in Euprotogonia but with the paraconid smaller, 



The dentition of the stem Perissodactyl thus resembled the Euproto- 

 gonia type more closely than any other and taken in connection with so 

 many other characters throughout the skeleton this dental resemblance to 

 Euprotogonia is significant of common origin. 



Diet. Possibly succulent tender herbage, berries, tubers, etc. Some 

 vestiges of the former animalivorous habits may have persisted. Even the 

 modern Peccaries, while relying chiefly on fruits and roots, " are by no means 

 adverse to varying their diet with carrion, worms, or insects" (Lydekker).' 



Brain case intermediate in wddth between that of Euprotogonia and that 

 of Eohippus. Because the brain of even the oldest Perissodactyls was 

 larger than that of the Condylarths, it might be objected that the former 

 w^ere therefore derived from some entirely unknown relatively large brained 

 "Cseneutherian" stock (p. 458); but the remarks made above (p. 310) touch- 

 ing the increase in size in the brain in the Carnivores seem to apply equally 

 well here. The large brained Perissodactyls are known to run back into 

 much smaller brained forms in the Lower Eocene and the Basal Eocene 

 Perissodactyls may reasonably be inferred to have had still smaller brains, 

 l)ut for lack of material this cannot be stated positively. Even among the 

 Condylarths there was considerable variation in the size of the brain, the 

 brain case of Meriiscotkerimn being relatively broader than that of Phena- 

 codus. It is not denied that the ancestral Perissodactyl hatl a larger brain 

 case and better brain than Euprotogonia. It is merely inferred that there 

 w^as a considerable variation in brain characters in the Condylarthra and 

 that the Perissodactyls sprang from some unknown, possibly Asiatic, larger 



1 The New Natural History. Vol. II, p. 443. 



