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. 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. That's the conclusion of Peter Larson from the Black Hills Institute of Geological Research in South Dakota, following his discovery of two distinct body types in T. rex .
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. The clincher will come later this year when the robust skeleton of Sue, the most complete T. rex ever found, goes on display at Denver Museum of Natural History. Finding that female tyrannosaurs were more stoutly built than males is not as surprising as it sounds.