58 



ORIGIN OF TOOTM PATTERNS 



" talon " ; and this ledge became produced into two additional 

 cusps, the hypoconule or hypoconulid, and the ectocone or ecto- 

 conid. Thus the typical sextuLerculate tooth of the primitive 

 Ungulate, and indeed of many primitive Eutheriaus, is arrived at. 



protoconid f\ _. protoconid 



paraconid jjl \ -—'m!aconid ^' 



prctocontd 



Fiu. 39. — Epitome of tlie evolution of a cusped tootli. 1. Reptile; 2, Broinatlienum ; 

 3, Micrnconodon : 4, JSpalacotherium : me. metacoiiid ; jjc^ jiaraconid ; pr, proto- 

 conid : h, A-nipihitlterium. (After Osboni. ) 



From this the still further complicated teeth of modern Ungulates 

 can be derived by further additions or fusions, etc.^ On the other 

 hand, the development of the Primate molar stops short at the 

 stage of four cusps. 



That such a series can be traced is an undoubted fact. Every 

 stage exists, or has existed. But whether the stages can be con- 

 nected or not is quite another question. It is by three main 

 lines of argument that the view here sketched out in brief is 

 supported. In the first place, the tracing of the pedigrees of 

 many groups of manniials has met with very considerable success ; 

 and it is clear that as we pass from the living Horse and 

 lihinuceros, with their complicated molars, to their forerunners, 

 we find that both can l)e referred to a primitive Ungulate molar 

 with but six cusps, (loing still further back to the lowest 

 Eocene and ancestral type as it appears, Eivprotogonia, we still 

 find in the molar tooth the sextubercular plan of structure. We 

 can hardly get further back in the evolution of the Perissodactyles 

 with any probability of seciu'ity. On the other hand, many facts 

 point to a fundamental relationship between the primitive Ungu- 

 lates and the early Creodonts. The latter frequently show plainl}- 

 tritubercular molars. Such Ungulates as EuprotOjfonia and Proto- 

 (/cmodon, though sex- or quinque-tubercular as to their molars, 

 have a distinctly prevailing trituberculisui, when the size and 

 importance of three of the cusps is taken into account. But tliis 



' c.(j. the " ]irotol(>])li," '•'inetalo])li." etc-, (sre Fig. 36, p. 51), of the inodcrn 

 Untrnlate form of tootli. 



