58 



MAMMALIAN DENTITION 



conodonts but it is no longer considered probable that such 

 a cusp migration took place in any other group of Mammals 

 recent or extinct. 



The Trituberculata 



The other group of Jurassic Mammals, known as the Tritu- 

 berculates, differs quite extensively from the Triconodonts. 

 Amphitherium Avhich is represented by the mandible only is 

 probably the most generalized species known. It appears to 

 have possessed five premolars and six molars, each of these 









pr d 



pa<* 



me d 



pr* 



pa* 



me* 



Fig. 15. — Lateral aspect, mandible of Amphitherium prevostii, Middle Jurassic, 

 England. (After Goodrich, Enlarged.) Restored right mandibular molar of Amphi' 

 therium, prevostii. (After Goodrich.) A. mesial aspect; B. lateral aspect; Abbrevia- 

 tions, a, angle; ac, condyle; cp., coronoid process; m., molars; me ! '., metaconid; mg., 

 groove for Meckel's cartilage; p., premolars; pa* 1 ., paraconid; pr d ., protoconid; Ta d ., 

 talonid. Note the bifanged character of the cheek teeth, a typically mammalian feature, 

 the conical premolars and the primitive tuberculo-sectorial molars. The angle in this 

 species is partly inflected. 



postcanine teeth being provided with two roots. The total 

 number of postcanine teeth is the same as in the Triconodonts 

 and in the Cynodonts previously described. Since the teeth 

 of the actual specimen are somewhat worn the enlarged re- 

 stored models (Fig. 15) give a better idea of the molars of 

 this animal. These differ greatly from the Triconodont molars. 

 The large central protoconid is very prominent and, as in the 



