RELATIONS AND HABITS OF M OS ASA URS 47 



allied — so far as the structure of the skull is concerned, present 

 a most striking resemblance to the mosasaurs, save perhaps in 

 the absence of pterygoid teeth. They have the same peculiar 

 form of the quadrate, similar teeth, similar frontal and parietal 

 bones, nares, and, most remarkable of all, the same peculiar 

 hinge in the lower jaws, unknown in other reptiles. Were the 

 vertebrae and ribs to be found in the Kansas chalk unassociated 

 with limb bones, they would almost without hesitation be 

 referred to the mosasaurs. The hands and feet have the same 

 strong resemblances in their form, but there is no hyperphalangy, 

 a character but feebly indicated in some of the mosasaurs. In 

 the elongated limb bones, and especially in the presence of a 

 true sacrum, the real differences between these reptiles are seen. 

 On the other hand, it is especially in those characters wherein 

 they resemble the mosasaurs that they differ from the monitors. 

 Like the mosasaurs, they have but seven vertebrae in the neck, 

 a number found in no other scaled reptiles. It is very certain 

 that they had webbed feet, though the claws had not dis- 

 appeared. 



That the varanids are a very old group, dating at least as far 

 back as the Jurassic, seems highly probable, especially so in the 

 light of the recent discovery of an iguanid lizard by Broom in 

 the Karoo beds of South Africa. As was long ago shown by 

 Boulenger, Beddard, and others, the Varanidae are an isolated 

 group among modern lizards, distinguished not only in the 

 structure of their skeleton, but also by many other characteristic 

 differences in their anatomy. 



In my opinion, there are no more striking examples of evo- 

 lution presented in all vertebrate paleontology than that of the 

 aquatic mosasaurs of the Upper Cretaceous, through the semi- 

 aquatic aigialosaurs of the Lower Cretaceous, from the terrestrial 

 varanoids of the lowermost Cretaceous or Upper Jura. 



That the snakes originated from the lizards much earlier than 

 we have any definite knowledge would seem very probable. We 

 have no certain evidence of them prior to the latter part of the 

 Upper Cretaceous, that is, the Laramie; but, since it now seems 

 almost certain that at least two distinct phyla of the lizards lead- 



