THE RELATIONSHIPS AND HABITS OF THE 

 MOSASAURS. 



There is, at present, no group of extinct reptiles which is 

 better known than that of the mosasaurs or pythonomorphs ; 

 there is no group concerning whose affinities and relationships 

 there have been more discussion and differences of opinion ; 

 and, also, the writer may venture to add, there is no group of 

 extinct vertebrates concerning whose phylogeny and taxonomic 

 position there is now less ground for dispute. The mosasaurs 

 are specialized aquatic lizards, descended from the immediate 

 ancestors of the modern monitors, through the extinct aigialo- 

 saurs, and which became wholly extinct near the close of Cre- 

 taceous time. They belong among the Lacertilio and are more 

 nearly related structurally and phylogenetically to the living 

 monitors than are the monitors to the living amphisbaenas or 

 chameleons. 



Whether the Squamata are an order, as is usually taught in 

 text-books, a superorder, as Fiirbringer and Osborn suggest, or 

 a subclass, as Gadow believes, scarcely affects the relations of 

 their component parts, nor the value of the group as a whole, if 

 all the other so-called orders of reptiles are raised to equal rank. 

 But to make the Squamata, a superorder, as does Osborn in a 

 recent publication,^ while leaving far more specialized groups, 

 such as the pterodactyls or turtles, in their former ordinal posi- 

 tions, is manifestly inconsistent. I know not what may be the 

 object of taxonomy unless to indicate the relative degrees of 

 divergence or of specialization of organisms; and to separate 

 the scaled reptiles from the Rhynchocephalia by superordinal 

 characters, while the far greater differences between the pterodac- 

 tyls and other reptiles, for instance, are accorded an ordinal value 

 only, is, in my opinion, unjustifiable. Nor can it be said that 

 the differences between a lizard and a snake have nearly as 



' Memoirs of (he American Museum of Natural History, Vol. I (N. 1903), p. 456. 



43 



