GLYPTODON, a gigantic extinct South American genus of edentate mammals, the type of a group, the Glyptodontia or tortoise-armadillos, in which the carapace is all in one piece, com posed wholly of polygonal bony plates united together without any of the movable rings of the armadillos. The skull is short, with deep jaw and fluted teeth (whence the name), the backbone is welded into a rigid tube, and a complex joint in the neck permits the head to be retracted within the shell as in tortoises. The limb bones are stout and the feet short, rounded, with hoofs instead of claws on the toes. In Glyptodon and the related Glyptotherium of North America there are four toes on each foot in front and five behind, and the tail is encased in a series of movable rings. Doedicurus, of the South American Pleistocene, the largest known glyptodont, has three toes on each foot in front and four behind, and a tail-tube covered by horny spikes. The pattern of the plates composing the carapace differs in each genus.
The glyptodonts originated in South America where they are represented during the middle and later Tertiary by smaller and more primitive genera. In the Upper Pliocene and Pleistocene they invaded North America as far north as the Southern United States, but are now extinct everywhere. (W. D. M.)