SUCCESSIVE MAMMALIAN FAUNAS 219 



of thick, bony plates, the huge carapace made up of innumerable 

 plates of bone firmly united at their edges and without the 

 movable bands of the armadillo carapace, the enormous tail- 

 sheath, the short legs and massive feet with broad hoofs, 

 must have given these animals rather the appearance of gigantic 

 tortoises than of mammals. The tglyptodonts were especially 

 numerous and varied in the Argentine pampas, and a stately 

 array of them is mounted in the museums of La Plata and 

 Buenos Aires ; in length, they ranged from six to twelve feet, 

 including the tail. The skeleton and carapace did not differ 

 very greatly in appearance among the various genera, but there 

 were great differences in the form and size of the bony sheath 

 enclosing the tail. In the genus \Glyptodon the sheath was 

 composed throughout of movable overlapping rings, with 

 prominent spines on them ; in '\Sclerocalyptus the hinder half 

 of the sheath coalesced into a single piece, marked only by 

 the elaborate ornamentation of the horny scales, while in 

 jDoedicurus the end had a tremendous, club-like expansion, 

 which must have been set with great horn-like spines. The 

 tglyptodonts were ponderous, slow-moving and inoffensive 

 plant-feeders, almost invulnerable to attack, and probably 

 used their massive tails, which could be freely swung from side 

 to side, as redoubtable weapons of defence, much as the alli- 

 gator uses his tail. In comparison with the bewildering variety 

 in South America, the few that made their way into North 

 America were quite insignificant. 



Much the same statement applies to the fground-sloths, 

 and though these ranged far more widely through the northern 

 continent than did the tglyptodonts, they were but few in 

 comparison with the multitude which inhabited alike the 

 forests of Brazil and the plains of the south. Two of the three 

 genera of tground-sloths which occur in the North American 

 Pleistocene, ^Megatherium and ^Mylodon, are also found in 

 South America ; and though ]Megalonyx has not yet been ob- 

 tained there, the family of which it is a member was represented. 



