76 MAMMALIAN DENTITION 



cophilus but their general plan is not quite the same nor is 

 the talonid so extensively reduced. The metacone and meta- 

 style in the upper teeth and the protoconid and paraconid of the 

 lower exhibit the typical carnivorous exaggeration and the 

 posterior border of the upper teeth is swung round as in Sar- 

 cophilus. The metaconid in the lower molars is nonexistent. 

 As can be seen from the retention of protocone and talonid in 

 unreduced form the last molar in both upper and lower jaws is 

 more developed than in Sarcophilus. Indeed in the mandible 

 the third molar presents the primitive character of being the 

 largest of the series and has the best developed talonid into 

 which fits the comparatively large protocone of the last upper 

 molar. 



The lengthening of the jaws, the presence and large size of 

 the third premolar and the characters of the molars just men- 

 tioned indicate at once that Thylacinus is no near relative of 

 Sarcophilus. Rather these two animals present in common a 

 carnivorous adaptation of the teeth but they have attained 

 some similarity in tooth form by quite dissimilar stages. (Even 

 their ancestors are only distantly related.) Sarcophilus is a 

 modified Dasyure and Phascologale represents a primitive stage 

 in its evolution. Thylacinus had with Phascologale a remote 

 common ancestor but that is the extent of the relationship. 



So far in tooth adaptation the emphasis has been placed 

 upon the shearing action of the trigon and trigonid. Next 

 must be considered the development of the grinding or trit- 

 urating action of the heel or talonid of the lower molar 

 in conjunction with the protocone of the upper. An example 

 of specialized omnivorous dentition is to be seen in Thalacomys 

 minor, a Rabbit Bandicoot (Fig. 21). The present specimen 

 is from South Australia. Its food consists of insects and worms 

 together with roots, bulbs, berries, fallen fruits and other 

 vegetable substances. In pursuit of these it must often dig 

 and this fact has given rise to the mistaken idea that the 

 animal lives in a burrow. It is about as large as a small rabbit, 



