HISTORY OP THE fTOXODONTIA 467 



The material from the lower Pliocene adds nothing to our 

 knowledge of the suborder, but in the Santa Cruz time of 

 Patagonia, which was Miocene, it was very abundantly repre- 

 sented and preponderatingly by the genus \Nesodon, which 

 was the first discovered member of the marvellous Santa Cruz 

 fauna, named nearly 70 years ago by Sir Richard Owen. 

 It so chanced that Owen's specimen was the imperfect lower 

 jaw of a young animal with the milk-teeth, which were mis- 

 taken for the permanent dentition, and when the latter was 

 found long afterwards, it was naturally supposed to belong to 

 a different animal and received a different generic name. Nor 

 was this all ; the changes which took place in the appearance 

 and relative size of the permanent 

 teeth within the life-time of the in- 

 dividual were so remarkable, that 

 the successive stages of development 

 were by several investigators sup- 

 posed to be distinct genera and 

 species and named accordingly. In 

 this way nearly 30 different names Fiq- 236.— skuU of Santa Cmz 



I , ,. ji 1 ttoxodont, tiV^esodon; same scale 



have, at one time or another, been of reduction as Pig. 235. 

 assigned to the common species, 



\N. imbricatus; and it was not until the late Dr. Ameghino 

 had brought together a complete series of skulls and jaws 

 illustrating these changes, and showing the gradual transition 

 from one to the other, that the confusion could be cleared up. 



There was a long hiatus in time between ^Toxodon and 

 \Nesodon and so great was the structural difference between 

 them, that there is much doubt whether the latter was directly 

 ancestral to the former; in any event, ^Nesodon so nearly 

 represents what the desired ancestor must have been, as to 

 serve for all practical purposes of the study. 



All the species of this Santa Cruz genus were much smaller 

 animals than the species of ■\Toxodon, ^N. imbricatus being 

 no longer than a tapir, with considerably shorter legs, and of 



