ADAPTATIONS TO SPECIAL ENDS 141 



the other hand, teeth of a markedly carnivorous type may be im- 

 planted merely in an undivided groove, as in the ichthyosaurs, 

 in which their crowns are generally conical and strongly fluted. 

 It seems probable that the thecodont mode of implantation 

 was originally confined to carnivorous forms ; the quadrupedal 

 sauropod dinosaurs, such as Brontosaurus and Diplodocus, in 

 which this mode of implantation occurs, possessing teeth which 

 might have been derived from those of a carnivorous type. On 

 the other hand, it must not be supposed that implantation in 

 sockets, or even in a groove, is characteristic of all carnivorous 

 reptiles, or that implantation in a groove necessarily implies the 

 existence of the latter habits. For instance, in the carnivorous 

 extinct sea-serpents (Pythonomorpha) the large and sharp 

 conical teeth were welded to the summits of the jaws in the 

 acrodont fashion ; while the teeth of the herbivorous iguanodons 

 were implanted in grooves. 



In connection with the teeth of the sea-serpents, it is impor- 

 tant to notice that among lizards and their allies the true acro- 

 dont type of dentition is generally associated with carnivorous 

 or insectivorous habits. For example, all the lizards of the 

 family Agamidce are carnivorous or insectivorous, as are also 

 the amphisbaenas and the chamseleons. The tuatera is also 

 apparently to some extent carnivorous. Perhaps, therefore, it 

 may be safe to assert that the thecodont and acrodont types of 

 dental attachment, and also the implantation in grooves, are to 

 a great extent correlated with carnivorous habits. 



On the other hand, it cannot be pretended that the pleuro- 

 dont type of attachment is correlated with herbivorous habits ; for 

 although this type of dental attachment occurs in the herbivorous 

 iguanas, it is equally manifest in the Lacertidce, Varanidce, and 

 Scincida;, most, if not all, the members of which are carnivorous or 

 insectivorous. It is, therefore, difficult to imagine why these two 

 types of dental attachment were evolved. The case of the 

 recent iguanas and of the extinct iguanodons apparently points, 

 however, to the conclusion that the pleurodont mode of implant- 

 ation and a peculiar form of tooth are not infrequently corre- 

 lated with herbivorous habits. For instance, the teeth of the 

 iguanodons present a certain resemblance to those of the iguanas, 

 while the mode of implantation of the former is only one step 

 from the pleurodont type. Again, the teeth of Scelidosnunis 



