South America has had an interesting history. After it had broken away from the ancestral supercontinent of Pangaea it remained an island continent for most of its life. It connected only occasionally to the continent of North America in the north, as it is today. At the end of the Cretaceous period the hadrosaurs spread over most of the continents and established themselves as the principal large herbivores, replacing the great four-footed sauropods. The sauropods still exist, but mostly in places where the hadrosaurs never gained a foothold, such as the South American continent. Isolated from the influences of migration from other continents, the sauropods evolved in their own way.The titanosaur group - the only surviving clade of sauropods - had begun to develop armor as early as the Late Cretaceous period. They continued to do so in South America and, in the Pliocene, with the arrival of the new meat-eaters during the Great American Interchange, the armor developed into very flamboyant and spectacular forms. The turtosaur has a solid shield of armor over its back and flanks. The tail and neck are also shielded, the tail by overlapping rings of horn, and the neck by jointed horn sections. The head is covered with a continuous horny shield. The jaws have no teeth, but the mouth edges of the horn shield are sharp and are ideal for cropping grass.