III.] 



TOXODONTS. 



idea of the huge size of these animals may be gathered from the 

 fact that the skull may measure as much as a yard in length. 

 Whereas Toxodon itself is confined to the Pampean beds, it is 

 represented in the somewhat older deposits of Monte Hermoso 

 and Catamarca by allied forms known as Toxodontotherium and 

 Xotodon. 



FIG. 1 6. SKULL OF Nesodon. Much reduced. 



In the Santa Cruz beds of Patagonia the place of the fore- 

 going is taken by the allied genus Nesodon, likewise belonging to 

 the same family Toxodontidce. In these animals, of which the 

 skull is shown in the figure, the molars retain marked resem- 

 blances to those of the rhinoceroses, which have been lost in the 

 more specialised Toxodon ; these teeth growing for a considerable 

 period, yet late in life developing roots in the ordinary manner. 

 The front teeth are very peculiar, the canines remaining small 

 throughout life, but the second pair of incisors in the upper, and 

 the third in the lower jaw growing beyond the others to form large 

 tusks in the adult, and never developing roots. In their rooted 

 molars the Nesodons depart less widely from the primitive Peris- 



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