SUCCESSIVE MAMMALIAN FAUNAS 247 



series, the fEntelonychia, is of great interest, for, as in the 

 fchaUcotheres of the northern hemisphere, the hoofs had been 

 transformed into claws and their five-toed feet had a truly 

 grotesque appearance, not diminished by the long and power- 

 ful limbs and relatively small head. 



This is the third example of that paradoxical creature, a 

 "hoofed animal" with claws instead of hoofs, and in each of 

 the three instances, there is every reason to believe, the trans- 

 formation proceeded independently. Among the perisso- 

 dactyls the fchaUcotheres (p. 238) underwent this change; 

 in North America the fAgriochceridse, a family of artiodactyls, 

 had a very similar history, while in South America the fEntel- 

 onychia arose from the same stock as the ftoxodonts, with 

 which they were nearly alhed. They were among the largest 

 animals of Santa Cruz times and ranged in size from an ox 

 to a rhinoceros. 



There was a fourth group, the f Astrapotheria, concerning 

 which our knowledge is tantalizingly incomplete, some species 

 of which were the largest of known Santa Cruz mammals, 

 while others were much smaller. They had short, domed heads, 

 with a considerable proboscis, and were armed with formidable 

 tusks, which were the enlarged canine teeth, the only known 

 instance of large canine tusks among the indigenous South 

 American hoofed animals. The limbs were long and not very 

 massive, the feet short, five-toed and somewhat elephantine 

 in appearance. These bizarre animals would seem to have 

 held a rather isolated position among the South American 

 ungulates, and though they may be traced back to the most 

 ancient mammal-bearing beds of that continent, their relation- 

 ships are still obscure ; much more complete material must be 

 obtained before this problem can be definitely solved. Both 

 the f Astrapotheria and the fEntelonychia died out shortly 

 after the end of the Santa Cruz. 



From many points of view the most interesting members of 

 the Santa Cruz fauna were the f litopterna, an order which also 



