MORRISON MAMMALS: PANTOTHERIA 



85 





between the upper and lower molars of this type and, without doubting the propriety 

 of referring the lower molars to the Pantotheria, he thus left the true nature and rela- 

 tionships of the family in the gravest doubt. 



We are now fortunately in a position to answer all the questions clearly raised by 

 Gidley and by Gregory. Not the slightest suspicion can attach to the association of the 

 upper and lower jaws as originally proposed by Marsh and supported by Gidley. By 

 actual trial it was possible to find two specimens, one of the upper and one of the lower 

 dentition, which fitted together almost as if they had come from one individual. The 

 occlusal relationships are thus clearly revealed and are brought out in the accompany- 

 ing figure. (Fig. 27.) 



Returning on this basis to the question of relation- 

 ships to the other, more normal, pantotheres, detailed 

 study reveals an underlying agreement imperfectly 

 masked by a great but superficial dissimilarity. All of 

 the original pantothere cusps, as seen, for instance, in 

 Dryolestes and Melanodon, are present and they retain 

 their original relationships, both to their fellow cusps of 

 the same tooth and to those of the occluding teeth. Super- 

 posed on this clear original pantotherian inheritance, 

 which leaves no valid basis for Gidley 's view of independ- 

 ent origin, there is a specialization, confusing but not 

 really profound. No new crests are developed and no 

 cusps are lost. All that has happened is a modification of 

 the proportions of the molars, broadening of the basins 

 and strengthening of the cusps, and the addition of one 

 small new cusp in the upper molars and of three small new cusps in the lower molars. 

 The result appears very bizarre to eyes accustomed to the repertoire of Tertiary molar 

 specialization, not because it is more profound, but because it departed from a more 

 primitive basis and did not exactly follow any of the lines of evolution illustrated in 

 later mammals. It must be regarded as a premature and ill fated effort toward the 

 production of broad-crowned crushing or grinding teeth from the more ancient pierc- 

 ing insectivorous type. 



The mandibular features are in exact agreement with this view. All the charac- 

 ters of the Amfhitheruim mandible are present, slightly modified, and on them are 

 superimposed some peculiar but superficial specializations. 



Since the above passage was first written, it has received important confirmation 

 by the discovery in the English upper Jurassic of a docodontid which approaches the 

 other pantotheres more nearly in molar structure than does Docodon itself. This genus, 

 Peraiocynodon (Simpson 1928B, p. 125), is a true member of the Docodontidae, with 

 the specialized lower molar heel and other characters of the family, but it retains a 

 narrower and more triangular trigonid with three main cusps. This trigonid is inter- 

 mediate in character between that of Ani-p hither ium or Peramus and that of Docodon, 

 although somewhat closer to the latter. 



Fig. 36. Premolar-molar tran- 

 sition in pantothere upper 

 teeth. A, Docodon. B, Mela- 

 nodon. 



