T. Rex's Killer Bite Revealed
February 29, 2012

T. Rex’s Killer Bite Revealed

Researchers from the University of Liverpool have revealed that the jaw muscles of Tyrannosaurus rex suggest that the dinosaur had the most powerful bite of any living or extinct animal.

The measurement, based on a laser scan of the dinosaur´s skull, showed that its bite was equivalent to up to 13,000 pounds -- four times more than previously estimated.

Publishing their findings in the journal Biology Letters, the team scaled up the skulls of a human, an alligator, a juvenile T. rex, and an Allosaurus to the size of an adult T. rex. In each case the bite forces increased as expected, but they did not increase to the level of the adult T. rex, suggesting it in fact had the most powerful bite of at least any land animal.

“Our results show T Rex had an extremely powerful bite making it one of the most dangerous predators to have roamed our planet,” musculoskeletal biologist Dr. Karl Bates told The Telegraph. “Models predict adult T. rex generated sustained bite forces of 35,000 to 57,000 (8,000 to 13,000 lbs.) Newtons at a single posterior tooth, by far the highest bite forces estimated for any terrestrial animal.”

The results also suggest adult T. rex had a powerful bite in both absolute and relative terms for its body size, and that biting performance increased during growth, allowing to kill and eat other big dinosaurs that existed at that time.

“The larger it grew the more it would have slowed down so its forearms got relatively smaller and its head bigger,” Bates told The Telegraph. “This adds to evidence that it would have hunted and killed beasts that were even bigger than itself such as Triceratops and the armored dinosaurs, possibly because it needed to prey on bigger animals to sustain itself.”

Bates, and his colleague, Peter Falkingham from the University of Manchester, found that the closest living creature that could exert a bite that rivaled T. rex´s, was the Nile crocodile, which has been measured at 5,000 lbs. (22,000 Newtons).

Even the Great White shark, the apex predator of the world´s seas, had a bite less than a third that of T. rex.

Previous analysis estimated T. rex´s bite force at around 1,800 to 3,000 pounds, but given the size of the beast, thought to weigh more than 13,000 lbs, researchers suspected its bite may have been more powerful than this. Using a computer model to reverse engineer the animal´s bite, researchers painted a clearer picture of the animal´s bite force.

Bite force is largely determined by the size of the jaw muscles. The researchers used the models to test a range of alternative muscle values, as it is not precisely known what the muscles of dinosaurs were really like. But even with error margins factored in, the computer model showed that the T. rex had a more powerful bite than previously suggested.

“Bite mechanics and feeding behavior in Tyrannosaurus rex are controversial. Some contend a modest bite mechanically limited T. rex to scavenging, while others argue that high bite forces facilitated a predatory mode of life,” Bates noted.

Using a life-sized copy of a T. rex skeleton exhibited at Manchester Museum as a model for their study, Bates and Falkingham used a laser scanner to digitize the skull and make a 3D model of it on their computer.

They then mapped muscles onto the computerized skull to recreate the snapping jaws of the prehistoric predator, reproducing the full force of a bite by activating the muscles to contract fully, snapping the jaws shut.

“Those [simulated] muscles closed the jaw as they would in life and... we measured the force when the teeth hit each other,” Bates explained to BBC Nature. He said the force generated from the bite is “equivalent to a medium-sized elephant sitting on you.”

Using the computer model, the researchers were able to see how T. rex´s bite force changed as it grew. The juvenile T. rex had a relatively weaker bite than the adult, which suggests feeding behavior also changed as it grew.

Juveniles possessed a lower, longer snouted skull than the adult. Expansion of the skull with maturity potentially provided greater volume for jaw-closing.

Analysis has also shown that younger individuals of T. rex were more athletic and agile than adults. With bite forces comparable to lions and alligators, combined with relatively long forelimbs and hindlimbs, juveniles were well equipped to pursue and dispatch small to medium-sized prey.

“Forelimbs became significantly reduced in adults, and our results strongly suggest increasing importance of the skull in food procurement as compensation,” said Bates. “Enhancement of an already highly competent biting apparatus during the exponential growth phase may be indicative of a change in feeding behavior as T. rex reached adulthood.”

“Living carnivores preying on large animals have relatively high bite forces, while carnivores preying on small prey have more moderate bite forces for their size, suggesting that bite force represents an important adaptation to differing feeding ecologies, at least throughout carnivoran evolution,” he explained.

Reaching an adult body size, combined with a specialized jaw anatomy underpinning high mechanical performance, may have allowed adult T. rex to function as a “large prey specialist,” alleviating direct competition from its smaller, more agile juvenile counterparts, and also from smaller carnivores in general.

“I think everyone expected T. rex to have a strong bite force, but it´s even stronger than we expected,” Dr Bill Sellers, who studies the physical capabilities of living and extinct animals at the University of Manchester, told BBC Nature. “And it gets stronger as it gets bigger, which is surprising.”

“The power of the T Rex jaw has been a much debated topic over the years,” said Bates. “Scientists only have the skeleton to work with as muscle does not survive with the fossil so we often have to rely on statistical analysis or qualitative comparisons to living animals which differ greatly in size and shape from the giant enigmatic dinosaurs like T Rex. As these methods are somewhat indirect it can be difficult to get an objective insight into how dinosaurs might have functioned and what they may or may not have been capable of in life.”

In conclusion, “our results show that the T. rex had an extremely powerful bite, making it one of the most dangerous predators to have roamed our planet. Its unique musculoskeletal system will continue to fascinate scientists for years to come,” said Bates.


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