T. rex’s incredible biting force came from its stiff lower jaw
A small bone in the mandible helped brace an otherwise flexible joint
By Sid Perkins
The fearsome Tyrannosaurus rex could generate tremendous bone-crushing bite forces thanks to a stiff lower jaw. That stiffness stemmed from a boomerang-shaped bit of bone that braced what would have been an otherwise flexible jawbone, a new analysis suggests.
Unlike mammals, reptiles and their close kin have a joint dubbed the intramandibular joint within their lower jawbone, or mandible. New computer simulations show that with a bone spanning the IMJ, T. Rex could have generated bite forces of more than 6 metric tons, or about the weight of a large male African elephant, researchers reported April 27 at the virtual annual meeting of the American Association of Anatomy.
In today’s lizards, snakes and birds, the IMJ is bound by ligaments, making it relatively flexible, says study author John Fortner, a vertebrate paleontologist at the University of Missouri in Columbia. That flexibility helps the animals maintain a better grip on struggling prey and also allows the mandible to flex wider to accommodate larger morsels, he notes. But in turtles and crocodiles, for example, evolution has driven the IMJ to be rather tight and inflexible, enabling strong bite forces.
Until now, most researchers have presumed that dinosaurs had lower jaws with a flexible IMJ, but there’s a big flaw with that premise, Fortner notes. A flexible jaw wouldn’t have enabled bone-crushing bite forces, but fossil evidence — including coprolites, or fossil poop, filled with partially digested bone shards — strongly suggests that T. rex could indeed chomp down with such forces (SN: 10/22/18).