One theory to explain the large South American animals involves locality. Scientists are excited about the possibility that environmental conditions differed greatly on all the continents, causing the animals to evolve even larger in South America because of that distinct environment. Just what those certain environmental conditions were is unknown. But if something in the environment truly caused distinct differences in the dinosaurs, there are probably many different types of dinosaurs still to be discovered all around the world. Only time will tell if scientists can determine the true reasons why the South American dinosaurs were giants of the Cretaceous world.