I 



PACHYRUCKOS 



137 



lieve that the confusion has arisen from the fact that these 

 Pyrotherium beds are set into the Guarantic, though of 

 much later age ; and from this fact, aggravated by the find- 

 ing of these two forms at about the same horizon, the 

 mistake of associating them has arisen. Also from failing 

 to recognize the time element in the separation Ameghino 

 put these beds in the Cretaceous instead of later, with all 

 the host of wrong conclusions, which followed from an 

 untrue assumption at the beginning of the argument; 



Skull of Pachyruckos 

 Three-fourths natural size 



for if Ameghino's few assumptions as to age of the beds 

 and certain affinities are granted the rest follows, especially 

 that almost every group of animals finds its origin in South 

 America; and we have a very unusual genealogy. 



There are also numerous other toxodonts, not so strik- 

 ingly strange as the above, but all very heavy, clumsy 

 animals with the front teeth specialized somewhat similar 

 to those of rodents and the back teeth developed into pow- 

 erful grinders. These grinding teeth are striking, in that 

 they are adapted to grow throughout life, which gave their 

 owner the opportunity to eat a very resistant type of food. 



Then there are numerous typotheres, which are little 

 animals about the size and build of a jack rabbit, except 

 that they have absolutely no affinities with the rabbits, 



