Evolution of the Herbivorous Dinosauria. 



275 



contributions 1 to our knowledge of the Dinosauria shows how the 

 teeth of the herbivorous members of that order have gradually 

 increased in complexity of structure, and as the author has kindly 

 allowed the use of some of the woodcuts illustrating his memoir, 

 we have great pleasure in laying before our readers a sketch of this 

 line of evolution. 



In the generalized suborder Sauropoda, which is mainly Jurassic 

 and died out after the Wealden, we find that the teeth, as in Morosaurus 

 (Diagram A, Fig. 1), are perfectly simple, having neither serrated 

 edges, nor carrying ridges on their lateral surfaces. In the generalized 

 Jurassic Stegosauria the teeth still retain the same simple structure, 

 but in the more specialised members of this suborder (e.g. Scelido- 

 saurns, Diagram A, Fig. 2), which occur in both the Jurassic and 

 Cretaceous, they have developed serrations on the edges, although 

 not distinct lateral ridges. The next step is presented by certain 

 members of the Ornithopoda, as Hadrosaurus (Diagram A, Fig. 3), 

 where a distinct vertical ridge is developed in addition to the 

 serrated edges. Advancing to the more specialised Ornithopoda-like 

 Iguanodon (Diagram B), we find that secondary lateral ridges are 



Fiq.i 



Fiq.3 



Ft C 



, 3 .i rtq.o rig. 2 



Diagram B. — Fig. 1. Tooth of Iguanodon Prestwichi ; from the enamelled surface. 

 Fig. 2 in profile. Fig. 3 section from x to y, \. a shows the principal 

 lateral ridge without serrations. 



developed ; and we may further observe that while in the Jurassic 

 I. Prestwichi both primary and secondary ridges are simple, in the 

 Wealden I. Mantelli the former has become serrated. The last step 



1 Ann. Soc. Sci. Bruxelles, 1835, pp. 309-338. 



V 



