56 CLTSP \0>[KNCI.ATURE 



even earlier representatives of these families. Fig. ?'G (p- 51) 

 illustrating a series of mammalian teeth will illustrate the abovt^ 

 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, however, 

 the difiiculties which beset such theorising are great ; that there 

 are such divergent and such strongly-held antithetical views is 



suliicient proof of this. Two 

 ^//^ main views hold the field : 



one, which has found most 

 favour in America, and is due 

 chiefly to the labours and per- 

 suasiveness of Professors Cope, 



l-ic. 38.— Molar teeth of A, /•Ae/ifcorfi/.s, and Sc(3tt, Osboru, and othsrS, is 

 B, ttie Greodont Pcchn'nnir.tis. Jiud, endo- <f j- -i 1 1 " 1 



conid; hid, hypocoimlid ; hyd, hypo- KUOWn aS tritu DerCUiy. 



conid ; m£d, metacoiiid ; jjn!, proto- rpj^^ alternative vicW, aS urged 

 conid. (After Osborn and Wortnian.) _ , _ . -.^ , , 



by lorsyth A'lajor, \\ oodward, 

 and (roodrich, 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 

 botli views, and something to be said against both. 



Tills (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 de^■elopment of trituberculy is proved. 

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

 that the Theromorpha represent more nearly than any non- 

 mammalian group with whicli we aie ao(.|uainted the probable 

 ancestral form of the mammals. These animals offer some 

 support to l3oth the leading views. Cynognatli/us had triconodont 

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

 intermedia,te stage in the e\'olution of trituliercular teeth ; on 

 the other hand, the teeth of Blademitdoii^ and some others are 

 multituberculate, and have been ver)' properly compared to the 

 multitubercular teeth of such primitive mammalia as the Ornitho- 

 rhynchus. Professor Osborn is no doubt correct in italicising a 

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

 Blodciiiodon the teeth, though multitubercular, show the pre- 

 valence of three cusps arranged in the tritubercular fashion. 



' See for a summary, Osboru, American Xnt. Dec. 1897, p. 993. 



