Young tyrannosaurs practiced biting as they waited for adult teeth

A new study from UC Berkeley reveals that young tyrannosaurs practiced their biting and strengthened their jaws before their adult teeth came in. The researchers determined that a juvenile Tyrannosaurus rex exerted a powerful bite force that was about one-sixth the force of an adult. 

Professor Jack Tseng teamed up with Professor Joseph Peterson of the University of Wisconsin to examine fossilized dinosaur bones that had teeth marks from a young tyrannosaur. 

The experts decided to replicate the bite marks and measure the force behind the bites. They developed a metal replica of a scimitar-shaped tooth of a 13-year-old T. rex, mounted it on a mechanical testing frame, and tried to crack a cow legbone with it.

“What we did, an actualistic study, is to say, ‘Let’s actually stab the thing with a tooth and see what it does,'” said Professor Peterson. “What we are finding is that our estimates are slightly different than other models, but they are within a close enough range – we are on the same page.”

After 17 successful attempts to match the depth and shape of the bite marks on the fossils, the scientists determined that young tyrannosaurs exerted up to 5,641 newtons of force, somewhere between that of a hyena and a crocodile. By comparison, an adult T. rex applied about 35,000 newtons of force, while humans exert about 300 newtons.

Bite force measurements can help paleontologists understand the ecosystem in extinct animals lived, as well as which predators ate which prey.

“If you are up to almost 6,000 newtons of bite force, that places them in a slightly different weight class,” said Professor Tseng. “By really refining our estimates of juvenile bite force, we can more succinctly place them in a part of the food web and think about how they may have played the role of a different kind of predator from their larger, adult parents.”

The study reveals that juvenile T. rexes were developing their biting techniques and strengthening their jaw muscles to prepare for using their adult teeth.

“This actually gives us a little bit of a metric to help us gauge how quickly the bite force is changing from juvenile to adulthood, and something to compare with how the body is changing during that same period of time,” said Professor Peterson. 

“Are they already crushing bone? No, but they are puncturing it. It allows us to get a better idea of how they are feeding, what they are eating. It is just adding more to that full picture of how animals like tyrannosaurs lived and grew and the roles that they played in that ecosystem.”

Professor Tseng emphasized that there is no one number describing the bite force of any animal – it depends on how the creature bites and adjusts the prey in its mouth for the best leverage.

“They probably were not just chomping down. If you look at modern predators, even reptilian predators, sometimes there is adjustment. Maybe they are finding the most mechanically advantageous place, or the strongest tooth to make their bite,” said Professor Tseng. 

“Presumably, there is some tuning involved before they make that bite, so they can literally take the best bite forward to make that kill or to damage whatever they are trying to get into.”

The measurements provide a starting point for charting the increase in young tyrannosaurs’ bite force as they mature.

“Just as you can do a growth curve for such an organism, you can also do a strength curve for their bite force – what was their bite force at 12 or 13 years old, what was it at 30, 35 or 40 years old. And what does that potentially mean about the role that those animals played in that ecosystem at the time?” said Professor Peterson. 

“What’s cool about finding bite marks in bone from a juvenile tyrannosaur is that it is tells us that at 13 years old, they weren’t capable of crushing bone yet, but they were already trying, they were puncturing bone, pretty deep. They are probably building up their strength as they get older.”

The study is published in the journal PeerJ.

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By Chrissy Sexton, Earth.com Staff Writer