The discovery of Giganotosaurus was important because it cleared up a mystery: why Tyrannosaurus rex had never migrated into South America. Both of these dinosaurs occupied the same position on top of the food chain, and it now appears that the roughly equal-sized Giganotosaurus kept the T. rex out of South America. In turn, T. rex kept Giganotosaurus out of North America. Other dinosaurs, such as the smaller theropods and larger herbivores, freely wandered between the two landmasses where there was a land bridge between them.