SUCCESSIVE MAMMALIAN FAUNAS 227 



the largest known representative of the order. Especially 

 characteristic was the abundance of the cavy family (Caviidae). 



The hoofed animals, with the single known exception of 

 the immigrant artiodactyl, all belonged to the autochthonous 

 orders, all of which are extinct at the present time. Fore- 

 runners of the extraordinary genus \Macrauchenia, which was 

 one of the most conspicuous elements of Pleistocene life, were 

 quite common in the Pliocene and differed from the Pampean 

 genus chiefly in their smaller size and less advanced specializa- 

 tion. We find here also the last survivors of another family of 

 the fLitopterna, the fproterotheres (fProterotheriidse), which 

 imitated the horses in such a surprising manner that some 

 authorities believe them to have been actually related to those 

 perissodactyls. The Monte Hermoso genus {'\E'pitherimn) had 

 feet which were wonderfully, though but superficially, like those 

 of the three-toed horses. The fToxodonta were numerous and 

 most of them were large, ponderous animals ; one genus {]Tri- 

 godon) had the interesting peculiarity of a single median horn 

 on the forehead, much like that of a rhinoceros. Horned spe- 

 cies were always rare among the indigenous groups of South 

 American ungulates, and all that have been discovered so far 

 belonged to the jtoxodonts. The remaining group, that of the 

 fTypotheria, was also well represented, both by larger and by 

 very small forms, some no larger than a rabbit {^Pachyru- 

 khos) . 



The presumably lower Pliocene (perhaps upper Miocene) 

 fauna of the Parana formation is as yet known only from very 

 fragmentary material. Representatives of the dogs, raccoons 

 and bears have been reported, but the identifications are doubt- 

 ful ; at all events, these would seem to have been the most 

 ancient of the northern immigrants. A considerable number 

 of marsupials, both opossums and large predaceous types, 

 have been found. The rodents were very numerous, all 

 belonging to South American families and some of them very 

 large. The edentates were gigantic fground-sloths and fglyp- 



