88 MOSTLY MAMMALS 



macrauchenia were certain contemporaneous ungulates from 

 Patagonia, of which the largest did not exceed a tapir in 

 size. With cheek-teeth so like those of the odd-toed 

 ungulates from the Paris basin described by Cuvier as 

 Palaeotherium, these Patagonian ungulates differed from 

 the macrauchenia in having the dental series reduced in 

 number and interrupted by gaps. Their most remarkable 

 peculiarity is, however, to be found in the structure of 

 their feet, which, in some forms at least, resembled those 

 of the extinct three-toed horses, or hipparions, in which 

 the middle toe is very large, while the two lateral ones 

 are small and functionless. In one genus, moreover, the 

 toes were reduced to a single large one on each foot, as 

 in the modern horse. And the fact that there existed in 

 South America a group of ungulates which exactly paralleled 

 the horses in the evolution and structure of their feet is 

 one of the most wonderful features in mammalian de- 

 velopment. 



Among all the extinct mammals of the Argentine, none 

 strike the beholder with more astonishment than those 

 gigantic cousins of the modern armadillos of South America, 

 collectively known as glyptodons, their name being derived 

 from the peculiar sculpture with which the grinding surfaces 

 of their cheek-teeth are ornamented. Both armadillos and 

 glyptodons differ from the other members of the group to 

 which they belong in having their bodies protected by a 

 bony shell, or carapace, covering all but the under-parts, 

 the top of the head being covered by a similar bony shield, 

 while the tail is encased by a series of bony rings, or in 

 rings at the base and a long tube at the tip. Whereas, 

 however, the armadillos (exclusive of the aberrant little 

 pichiciago) have a larger or smaller portion of the middle 

 region of the carapace formed of movable transverse bands 



