172 



KVOIA'TIOX OF MAMMALIAN MOLAR TKKTH 



As the name indicates, the upper molars are triangular ; the inferior 

 molars exhibit a well defined trigonid, with the paraconid reduced but 

 still distinct, in fact the teeth are almost tuberculo-sectorial. Comparison 

 of a series of lower molar teeth of species belonging to this genus 

 (T. metsiacus, T. ctsayicus) show a progressive degeneration of the 

 paraconid, depression of the trigonid, and elevation of the talonid : 

 in other words, the development of a bunodont crown (Fig. 152). 



Fin. 154. Upper and lower cheek teeth of Bv.nomtry.f ile<i.iix, from the Uinta Formation 

 (Upper Eocene), a small bunoselenodont Artiodactyl. Note the crescentic outer cusps, the large 

 crescentic intermediates (j>l. ml.), especially the very large mctaconule which is preoccupying the 

 position usually assumed by the hypocone, which here remains minute (/<//). x 1. After Wortmau. 



}?l / 



Fio. 155. Upper molars of Anthracotherium Icun.ise, a bunoselenodont Artiodactyl from the 

 Protoceras Beds, Upper Oligocene, showing the greatly enlarged metaconule, which takes the 

 place of a hypocone. (Cf. Bunomtryx, Fig. 154.) xi. 



Fir;. 150. Principal types of molars among Artiodactyls. 



A. Bunodont. All cusps conic. Examples Primitive Suilliiies (Elotherium, Peccaries, etc.). 



B. Bunoselenodont. Outer cusps only crescentic, inner cusps conic, or subcrescentic. Example, 

 Aiithracotheres (A i < << ' / ' s ). 



C. Selfiwdoiit. All cusps crescentic. Examples, J\Iu->/coj>otamus, Deer, Antelopes, Camels. 

 In C'the cusp marked h;/ appears to be the enlarged metaconule. (Cf. Figs. 154, 155.) 



In the Eocene Helohyus the molars are fully bunodont, that is, 

 with low, rounded cusps ; the paraconid is extremely minute. The 

 series also shows the progressive molarization of the premolars and 

 lends support to the theory that the molar pattern was originally 

 triangular, and sharply differentiated from the premolar pattern, and 

 that the premolars are becoming molariform by adding the cusps in 

 a different order from that of the molars (see pp. 194, 195). 



