He offers a different rationale for the stoutly built skull, which also explains how tyrannosaurs managed to break up their prey despite their lack of effective grasping forelimbs. He believes they tore their victims apart by seizing them in the mouth and shaking them violently - rather like many of today's marine predators that also feed without the help of limbs, such as sharks and killer whales. Enormous forces would have acted upon the skull and neck, putting a premium on size and strength. Larger prey wouldn't have been shaken, but chunks of flesh would have been gouged out with the teeth, he says. Family life Female tyrannosaurs were larger than males.
Further evidence comes from a living descendent of dinosaurs.
Male crocodiles have an extra bone known as a chevron at the base of their tail where the muscle that retracts the penis is attached. The same is true of saurornithoides, a group of dinosaurs from China that are closely related to tyrannosaurs. Larson is looking for a similar pattern. Finding that female tyrannosaurs were more stoutly built than males is not as surprising as it sounds. Larson points out that, contrary to most people's expectations, throughout the animal kingdom females tend to be larger than males, because of the obvious advantages for laying eggs or carrying young.