136 E VOLUTION OF MAMMALIAN MOLAR TEETH 



crown, in which the trigonid or triangular arrangement is still 

 perfectly apparent and the broad heel or talonid is still per- 

 sistent in these three characteristic cusps. In the types repre- 

 sented in C and I) the heel has begun to degenerate. In E the 

 talonid has become very simple, the inetaconid is degenerating, fthe 

 trigonal arrangement has been lost because the paraconid is rotating 



FIG. 91. Upper and lower teeth of a Creodont, Hitienml.on. Carnassial teeth, (first and 



second upper, and second and third lower molars). The perfected carnassials -^ are shaded. 

 After Matthew. 



FIG. 91 Upper and lower teeth of a Creodont, O.ma MI. Carnassial teeth . (First upper 



IK* 



and second lower molar). After Matthew. 



outward and forward, lending support, by the way, to the cusp 

 rotation theory (p. 32 (6)). In F (Dinidis) the paraconid is nearly 

 subequal with the protoconid, and the metaconid is vestigial, while the 

 talonid is still further reduced. In G (Fclis) the metaconid is altogether 

 wanting, the talonid is vestigial, the paraconid and protoconid are in the 

 same fore-and-aft line, of nearly equal size, and sharply lophoid or sectorial. 

 The i-irniassicd specialization in this case involved the development or 



