142 



EVOLUTION OF MAMMALIAN MOLAR TEETH 



me. 



pa. 



m.2 



m.l 



pr. 



de. 



Fig. 102. Crown view of the right upper cheek teeth of the Binturong (Aretictis binturong), 

 showing the loss of the third molar, the great reduction of the second (;-), the simplification of 

 the first (/i) by the loss of the metacone (mi), and the reduction of the protocone (pr), the con- 

 vergence in form between i/(i and p4, the greater or less flattening down of the crowns of p^ mz ; 

 all this apparently in adaptation to frugivorous diet. The nearest allies of the Binturong, the 

 Paradoxures, have more normal teeth, while the most primitive, more carnivorous members of 

 the family Viverridre (.</. <i> n< tta) have tritubercular upper and tuberculosectorial lower molars. 



FlSSIPEDIA. 



The tritubercular and tuberculo-sectorial teeth of primitive Procyon- 

 iclse, Mustelidte, Viverridte, Ursida?, Canida3, Felidre, and Hysenidte are 

 too well known to require special emphasis. In general the Procyonida? 

 exhibit the bunodont, tritubercular type. The Ursidae exhibit a 

 depressed and secondarily bunodont, quadri tubercular and tuberculo- 

 sectorial dentition ; as seen by comparison of the more sectorial molars 

 of the Polar Bear, Thalassarctos, with the more depressed molars of the 

 relatively omnivorous Black Bear. The teeth of the bear were originally 

 more elevated like those of the dog, then secondarily elongated, and 

 finally depressed and irregularly tubercular. 



Degenerate Types. 



Adaptation to different habits has given rise to a great variety of 

 secondary modifications. For example, (1) to the flat or even basin- 

 shaped crown of Gercolcptcs, (2) to the degenerate tuberculate teeth 

 of Aretictis (Fig. 102); the extreme similarity between p 4 and m 1 in 

 this animal, the enlargement of the paracone and the reduction of 

 the metacone, the ledge-like appearance of the protocone, make the 

 resemblance which has arisen between these teeth analogous to that 

 which has arisen in Mesony.r, namely it is a case of convergence. 1 



In general answer to the analogy argument (p. 215) it has been 

 shown in the case of the sectorials of Creodonta and Fissipedia above,. 

 that (a) final similarity of form is no indication of derivation from 

 homologous parts ; (b) the exact similarity of p* and m 1 in Aretictis 

 (Fig. 102) is another case of independent or convergent evolution, or the 

 production of analogous crowns from non-homologous cusps (see pp. 

 138, 139); (c) fruit-eating habits (Aretictis is said to be frugivorous) 

 frequently lead to the degeneration or aberrancy of the molar crowns 



l [But see also the indications in Figs. 14, 66. 67, 69a, 76, 84, 85, 105, 116, 117, 

 118, 131, 139, etc., that the similarity between p 4 and m 1 is not wholly due to convergent 

 evolution. ED. ] 



