HISTORY OF THE fTOXODONTIA 463 



Suborder fToxoDONTA. fToxoDONTS Proper 



Among the remarkable animals which Charles Darwin 

 found in the Pampean deposits of Argentina and took with him 

 to England, was a skull of one which Sir Richard Owen named 

 \Toxodon, or "Bow-Tooth," from the strongly curved grind- 

 ing teeth, those of the opposite sides almost meeting in the 

 median Une above the hard palate. For many years '\Toxodon, 

 of which hardly anything was known, save the skull and teeth, 

 was a zoological puzzle and no one was able to reach any satis- 

 factory conclusion as to its systematic position and relation- 

 ships, as all the attempts made to force it into one of the known 

 ungulate groups were obvious failures. The discovery of 

 complete skeletons, two of which are mounted in the La Plata 

 Museum, showed the necessity of making a new group for its 

 reception, as Owen had originally proposed. Through the 

 exploration of Argentina and its Patagonian provinces, the 

 history of the suborder was followed far back into the Tertiary 

 period and its indigenous character demonstrated. This and 

 all the other subdivisions of the fToxodontia were exclusively 

 Neotropical in distribution, and none have been found farther 

 north than Nicaragua and there only in the Pleistocene. 



The suborder was represented in the Pampean beds by 

 several genera, which differed in size and in the complexity of 

 the grinding teeth, but only of ^Toxodon is the skeleton at 

 all fully known. The Pampean species of this genus were 

 massive, elephantine creatures, rivalling the largest rhinoceroses 

 in bulk, but not equalling them in height. The teeth were all 

 thoroughly hypsodont and apparently continued to grow 

 throughout life without forming roots; the dental formula 

 was : 1 1, c ^, p f, m f , X 2 = 34. The first upper incisor was 

 broad and chisel-shaped, the second more tusk-like, but in some 

 species these proportions were reversed ; the lower incisors 

 were procumbent, pointing straight forward, and of these the 

 third was the largest. The canines were lost and there was a 



