284 THE DENTAL SYSTEM OF THE PRIMATES [SECT. A 



Later research has shewn that this statement is too general, since 

 minute cusps may and do supplement the principal prominences 

 first observed (cf. Fig. 203 Pl, Hy, Hd, and End). And again 

 the difference in form between the upper and lower teeth is 

 considerable 1 . But even with these objections, the generalization 

 was supported as being justifiable 2 . 



(ii) Fossil mammals of even greater antiquity than those of 

 the Basal Eocene beds of Puerco were known even when Cope 

 first advanced his theory. On examining the fossil remains of the 

 Mesozoic (Jurassic) mammals, Cope arrived at the conclusion that 

 the three-cusped tritubercular type of molar tooth observed by 

 him, had arisen from a tooth of simple conical form (haplodont) 

 by the addition of lateral denticles (Fig. 204). 



1 1 3 



Fig. 204. Diagram shewing the derivation of a tritubercular (triconodont) tooth 

 (No. 3) from a simple cone (No. 1). No. 2 shews the primitive alternation of upper 

 and lower teeth. No. 3 is a tooth of Dromatherium. (From Osborn.) 



(iii) Then it became necessary to account for the presence of 

 these denticles. Cope supposed that they arose from the original 

 undivided cone. This view has been greatly disputed. The most 

 important alternative is embodied in a view which is distinguished 

 as the theory of Concrescence. The name of Dr Rose is specially 

 associated with this theory. It postulates the fusion of a number 

 of simple cones situated originally in close proximity to each other. 

 The theory of Concrescence is discussed in the sequel, and will 

 not be considered further here 



1 Gregory points out that the upper teeth have three cusps and belong to a type 

 since termed tritubercular; the lower molars represent a modi fication of that type 

 known as the tuberculo-sectorial variety. 



'-' Matthew, Bulletins of the American Museum of Natural History, Vol. xxxi. 

 1912, pp. 307-314, lays stress upon the great antiquity of the triangular type of 

 molar tooth, as exhibited by the Puerco Eocene Insectivore Palaeoryctes puercensis. 



