If you have ever been in front of a complete fossil of a Tyrannosaurus rex, there is no doubt that he was the apex predator of his era. The adults were huge, with giant skulls and serrated teeth the size of bananas. The force of an adult T. rex’s bite has been the subject of numerous studies, but mysteries persist about what led to the powerful bite that dominated the end of the Age of Dinosaurs.
In research published in September in the journal The Anatomical Record, a team of scientists sought to understand the oral arsenals of tyrannosaur species that roamed Asian and North American landscapes for millions of years before T. rex. By analyzing biting forces and the stress that all this devouring placed on the tyrannosaurs’ skulls, researchers showed that they gradually increased their bone-crushing power over the eons. They also discovered that even in its juvenile form, the T. rex was capable of delivering a really nasty bite.
It was not easy for researchers to construct 3D skull models of nine species of tyrannosaurs for their analysis. Evan Johnson-Ransom, a doctoral student at the University of Chicago who led the research, said that just reconstructing digital skulls from two Asian species “took approximately three months, as we had to work with flattened specimens.”
But the team persisted, coming to the conclusion that tyrannosaurus snouts fit into two basic shapes: gracile for those that were more slender, like earlier forms of tyrannosaurus and juvenile T. rex; and robust for heavier snouts, like that of an adult T. rex. Each 3D model was then subjected to finite element analysis, a technique that determines stress and strain in biological structures. Stress, in this context, refers to the amount of force exerted on the bones of the skull, which were capable of handling extreme efforts.
Under moderate to high stress, the skulls are “doing a lot of biting or a lot of heavy lifting during feeding,” Johnson-Ransom said. Lower stress indicates that one species of tyrannosaur was not biting as hard as others were.
Some of the results were expected: the larger the tyrannosaur species, the greater the bite force.
Other results were more surprising: The shape of a snout didn’t necessarily correlate with stress on the skull. In fact, some of the earliest graceful-snouted tyrannosaurs had low stress on the skull, suggesting “they didn’t bite as hard,” Johnson-Ransom said. But when a beast like T. rex tore prey apart with its bite, the stress on its skull was high.
Emily Rayfield, a professor of paleobiology at the University of Bristol in England who was not involved in this study, praised the researchers for overcoming past technological limitations with their analysis. But the T. rex results surprised her.
“Their wider skulls have more jaw-closing muscles, which means they can bite proportionally harder,” she explained, “but their skulls remain relatively stressed as a result.”
“Before reaching robust adulthood, a young T. rex had a gracile snout. The new research highlighted how a young T. rex’s feeding abilities allowed it to occupy a different ecological niche than the one in which it would thrive in old age. adult, when its skull and bite could handle larger prey.”
But even when young, the study showed that T. rex had jaw muscle strength capable of producing stronger bites than any of its non-rex tyrannosaur ancestors. This was a powerful predator regardless of age.
Other researchers said this discovery could be one of the most valuable parts of the study.
“O Tyrannosaurus adult did not exist in a vacuum,” said Thomas Holtz, a vertebrate paleontologist at the University of Maryland who was not involved in the research. “Every adult T. rex had to survive as a baby and a juvenile first, and the adult T. rex itself Tyrannosaurus It was the product of a long evolutionary history.”
The authors hope their methods can be applied to other, less studied dinosaurs. Johnson-Ransom has already started, showing at an October meeting of the Society of Vertebrate Paleontology what finite element analysis can tell us about Spinosaurus, huge carnivores that had large sails on their backs.