184 



EVOLUTION OF MAMMALIAN . MOLAR TEETH 



CHALICOTHEKOIDEA OR ANCYLOPODA. 



The Ancylopoda are apparently a group of aberrant Perissodactyla 

 in which the nails or generalized hoofs have become secondarily 

 modified into large claws. The types of this order are the genera 

 Macrotherium, Ckalicotherium, and Anci/lotherium, in which the superior 

 molar teeth exhibit a strong general resemblance to those of 



FIG. 1S3. Bunoselenodont upper cheek teeth of Meniscotherium tcrrcerubrce, a Condylarth (?), 

 from the Wasatch Formation, Lower Eocene. Note the large selenodont protoconule, the oblique 

 metaconule-hypocone ; in the lower molars, the twinning of the metaconid (me<t), a feature also 

 independently developed in the Equidas, Fig. 166. x. 



ml- 



,-ps. 



,pa. 



pl. 



by- 



pr. 



Fio. 184. Buno-lopho-selenodont molar (ufl) of Schizotheriwn modicum, an Ancylopod from the 

 Eocene of France. In the drawing the height and size of the protocone and hypocone is consider- 

 ably foreshortened. 



Titanotheres among Perissodactyla : that is, they are buno-selenodont 

 (Fig. 184), or, strictly speaking, buno-lopho-selenodont, because they 

 combine bunoid, lophoid, and selenoid modelling of the cusps. These 

 molars have evidently evolved from a sexitubercular ancestral type, 

 and we reason by analogy that they were of tritubercular origin. 



In Meniscotherium we have a genus of much greater geological age, 

 which exhibits a somewhat similar type of grinding tooth (Fig. 183). 

 It has been considered by Osborn for this and other reasons as a 

 possible ancestor of the Ancylopoda, though still a member of the 

 order Condylarthra. However recent observations tend to show that 

 these resemblances are not indicative of genetic relationship but that the 



