Giant predators like Tyrannosaurus Rex and Giganotosaurus get all the press, but it's a fact of nature that the meat-eating “apex predators” of any given ecosystem are tiny in number compared to the plant-eating animals they prey on (which can rely on the vast amounts of vegetation needed to sustain such large populations).
By analogy with modern habitats in Africa and Asia, herbivorous hadrosaurs, ornithopods and (to a lesser extent) sauropodsprobably roamed the Mesozoic Era in crowded herds, and were hunted by sparser packs of large, small and medium-sized theropods.
