VERTEBRATE PALEONTOLOGY IN 1913 643 



under the name of G. fraasi. It differs from the American 

 species by the teeth being laterally compressed, instead of 

 hemispherical. In both cases the food probably consisted, 

 according to Prof. Dollo, of echinoderms ; such a diet being, 

 of course, indicative of diving habits. In the allied genus 

 Plioplatecarpus, belemnites and other cephalopods may have 

 constituted the staple food, in which case these reptiles would 

 likewise have been divers. On the other hand, the members 

 of the typical genus Mosasaurus, in which the dentition is of 

 a highly carnivorous type, were probably fish-eating surface- 

 swimmers. 



In connection with this part of the subject, reference may 

 be made to a paper by Dr. R. Broom (Bull. Amer. Mus. Nat. 

 Hist. vol. xxii. pp. 507-8) on the squamosal and associated 

 bones of mosasaurs and lizards, in which the author endorses 

 the view that the outermost of the two bones which have 

 been alternately regarded as representing the squamosal is 

 really that element. This view is strongly supported by the 

 condition obtaining in the carnivorous anomodonts, in which 

 the structure of this region is so mammal-like as to leave no 

 doubt which bone is the squamosal, and the outermost of the 

 two bones in the corresponding region of the skulls of lizards 

 and mosasaurs appears to be the homologue of the former. 

 If this be correct, the inner bone will apparently represent 

 the tabulare ; and as this is a primitive element, it would 

 seem to follow that lizards are really a very ancient group. 



The preceding paragraph naturally leads to the consideration 

 of a letter from Dr. Broom, published in Nature on the vomer 

 of dicynodonts. After referring to the fact that a pair of 

 bones — the prevomers — in the fore part of the palate of lizards 

 seem to represent the two elements in the mammal Ornitho- 

 rhynchus which eventually unite to form the so-called dumb-bell 

 bone, the author proceeds to observe that while some of the 

 carnivorous anomodonts seem to have a single mammal-like 

 vomer and a pair of bones in front, in the dicynodonts only 

 the former element is present ; other carnivorous forms (thero- 

 cephalians), on the contrary, have a pair of large anterior 

 elements and no median bone. To solve the problem a specimen 

 showing a large median true vomer and a pair of prevomers 

 was essential, and this has turned up in the shape of a dicy- 

 nodont skull in which the median element lying between the 



