CUSP XOiMENCIATURE 



Fill. 38. — Molar teeth of A, Phenacodus, and 

 B, tlie Creodont Palaeonictis. End, endo- 

 couiJ ; h,ld, liypocoiiulid ; hyd, liypo- 

 conid ; med, metacoiiid ; i^rd, proto- 

 conid. (After Osliovn and Wortnian.) 



even earlier representatives of these families. Fig. 3 (J (p. 51) 

 illustrating a series of mammalian teeth will illustrate the above 

 remarks. That there is such a convergence in tooth structure 

 shows that it is, theoretically at least, possible to determine the 

 ancestral form of the mammalian tooth. Practically, liowever, 

 the difficulties which beset such theorising are great ; that there 

 are such divergent and such strongly-held antithetical views is 



sutticient proof of this. Two 

 ^!/^ main views hold the field : 



one, which has found most 

 favour in America, and is due 

 cliiefly to the labours and per- 

 suasi^eness of Professors Cope, 

 Scott, Osborn, and others, is 

 kuown as " trituberculy." ^ 

 The alternative view, as urged 

 liy Forsyth Major, Woodward, 

 and Goodrich, attempts to show that the dentition of the 

 original mammal included grinding teeth which were multi- 

 cuspidate or "multituliercular." There is much to be said for 

 l)oth views, and something to be said against both. 



This question is, however, wrapped up in a wider one. Its 

 solution depends upon the ancestry of mammals. If the Mam- 

 malia are to be derived from reptiles with simple conical teeth, 

 then the first stage in the development of tritulierculy is proved. 

 On the other hand, however, the e^'idence is gradually growing 

 that the Theromorpha represent more nearly than any nou- 

 mammalian group with which we are ac(|uainted the probable 

 ancestral form of the mammals. These animals offer some 

 support to both the leading views. Cynognathns had triconodont 

 teeth which, as will be pointed out later, are a theoretically 

 intermediate stage in the evolution of tritubercular teeth ; on 

 the other hand, the teeth of Diadeinodon and some others are 

 multituberculate, and have l)een very properly compared to the 

 multituljcrcular teeth of such ])rimitive mammalia as the Ornitho- 

 rhynchus. Professor Osborn is no doubt correct in italicising a 

 remark of an anonymous writer in Science to the effect that in 

 Diademodon the teeth, tliough multitubercular, show the pre- 

 valence of three cusps arranged in the tritubercular fashion. 

 ' Sec I'or a aumiuary, Osborn, AmericaiL Xal. Dec. 1897, p. 993. 



