142 REPTILES 



and its allies, which are distant relatives of the iguanodon, 

 are decidedly like those of the iguanas, having compressed 

 crowns with finely serrated edges ; while the spatula-shaped teeth 

 of Diplodocus, Hoplosaurus, and Brontosaurus, which may have 

 been herbivorous, may be compared with See lido saurus-tQe\h 

 which had lost their serrations and become spoon-shaped by 

 the pressing-in of one lateral surface. Reverting to the pleuro- 

 dont type, it may be mentioned that in the family Scincidce the 

 Australian stump-tailed skink (Trachysaurus rugosus) will con- 

 sume vegetable food, such as lettuce ; and, judging from the 

 large flat-crowned teeth, it seems probable that the species of 

 the Australasian genus Tiliqua may at times vary their diet with 

 vegetable food, although they appear to be mainly insectivorous. 



Be this as it may, it is noteworthy that the teeth of truly 

 herbivorous reptiles are adapted for masticating, and conse- 

 quently become worn down, this being markedly the case with 

 those of the Galapagos sea-iguana (Amblyrhynchus), which feeds 

 on sea-weed, and still more so with those of the iguanodon. 

 Here it may be remarked that, with the possible exception of 

 those of the mammal-like group (Anomodontia), the teeth of 

 reptiles, unlike those of mammals, are replaced irregularly and 

 continuously, the crowns of new ones growing up alongside of 

 or below the old ones as the latter become worn out and useless. 



It remains to notice certain types of reptilian dentition which 

 are evidently special adaptive modifications, although it is by 

 no means easy to indicate the object of the adaptation. Firstly, 

 we may notice the rhynchocephalian tuatera, in which, as already 

 mentioned, the dentition is of the acrodont type. Both jaws 

 are furnished with a pair of chisel-like teeth at the front ex- 

 tremity. The edge of the lower jaw is surmounted by a single 

 row of closely crowded teeth ; but in the hind part of the upper 

 jaw there are two parallel rows of such teeth, separated from 

 one another by a longitudinal groove. When in use, the lateral 

 series of lower teeth bites into the groove between the two upper 

 rows ; and when the teeth become much worn away (and there 

 seems to be little replacement), the edge of the upper jaw itself 

 becomes ground down and forms a sharp cutting instrument. 

 The precise use of this complicated arrangement is not apparent. 

 In captivity tuateras greedily devour meal-worms and other 

 insects, but it is believed that vegetable substances form at least 



