Tyrannosaurus rex delivered bone-crushing bites with stiff jaw, research suggests

The tyrannosaurus rex’s bone-crushing bite strength came through keeping a joint in its lower jaw steady like an alligator, rather than a flexible mandible like that of a snake, a new study has suggested.

Paleontologists have long been puzzled over how the dinosaur’s jaw was strong enough to bite through and ingest bone - as fossil evidence showed it did regularly.

Scientists had found that the T. rex had a joint in the middle of their jaws, called the intramandibular joint, which is also present in modern-day reptiles.

Previous research suggested this joint was flexible, as it is in snakes and monitor lizards, but new research has questioned that theory.

“We discovered that these joints likely were not flexible at all, as dinosaurs like T. rex possess specialised bones that cross the joint to stiffen the lower jaw,” John Fortner, a doctoral student in anatomy at the University of Missouri and lead author of the study, said.

The researchers used CT scans of dinosaur fossils and modern reptiles to build a detailed 3D model of the T. rex jaw, with simulated bone, tendons and specialised muscles that wrap around the back of the jaw.

Mr Fortner said that the research had modelled dinosaur jaws in a way that had never been done before.

“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,” he said.

The research will be presented at the American Association for Anatomy annual meeting during the Experimental Biology (EB) 2021 meeting, held virtually from 27 April to 30 April.

A previous study, published in the journal The Anatomical Record in 2019, found that the T. rex could bite down on prey with a force upwards of seven tonnes.

In order to see whether the intramandibular joint could maintain flexibility under the forces required to crunch through bone, the research team for the 2021 study ran a series of simulations to calculate the strains that would occur at various points depending on where the dinosaur’s jaw hinged.

Their findings suggested that bone running along the inside of the jaw, called the prearticular, acted as a strain sink to counteract bending at the intramandibular joint, keeping the lower jaw stiff.

“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,” Mr Fortner added.

“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.”

Additional reporting by PA