How did T. rex break bones with its bite?

The Tyrannosaurus rex might be known for its ferocity and its mouth full of serrated teeth, but how did it actually bite? New research suggests the T. rex might have crunched like an alligator.

Similar to modern day reptiles, dinosaurs had a joint in the middle of their lower jaw called the intermandibular joint. Palaeontologists have puzzled over how this joint was used by T. rexes to crunch bones, even wondering whether it could have been flexible like a snake’s.

According to new research, presented at the American Association for Anatomy’s annual meeting, it was probably stiff like an alligator’s.

“We discovered that these joints likely were not flexible at all, as dinosaurs like T. rex possess specialized bones that cross the joint to stiffen the lower jaw,” says John Fortner, from the University of Missouri in the US, who led the study.

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The researchers used CT scans of dinosaur fossils and modern-day specimens to create a 3D computer model of a dinosaur jaw and identify where muscles attach to bone. They then used the model to simulate muscle forces under different biting scenarios. Stars indicate areas where strain was assessed. Credit: Image courtesy of John Fortner, University of Missouri.

The team used CT scans to analyse dinosaur fossils and compare them to modern day reptiles. They then built a 3D model of the T. rex jaw, including bone, tendons and muscles.

Using the model, the team simulated the jaw movement when it was hinged in different places and calculated how much strain the jaw would be under to break bones in each position.

The results showed that a bone on the inside of the jaw, called the prearticular, eased the strain of crunching bones when the intermandibular was bending, which probably also kept the lower jaw stiff by anchoring it in place.

“We are the first to generate a 3D model of a dinosaur mandible which incorporates not only an intramandibular joint, but also simulates the soft tissues within and around the jaw,” Fortner says.

“Because dinosaur mandibles are actually built so much like living reptiles, we can use the anatomy of living reptiles to inform how we construct our mandible models.

“In turn, the discoveries we make about T. rex’s mandible can provide more clarity on the diversity of feeding function in today’s reptiles like crocodilians and birds.”

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