T-rex jaw © Getty

The T. rex didn’t get its bone-crunching bite until adulthood

New research has demonstrated a juvenile Tyrannosaurus Rex jaw was much less powerful compared to adults.

Turns out the Tyrannosaurus Rex wasn’t as powerful as you might think. Well, at least the younger ones. According to new research from the University of Bristol, before adulthood, the formidable dinosaur was not capable of delivering a bone-crunching bite.

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Using 3D modelling based on previously found bones, scientists determined that while a fully-grown T. rex could deliver a force of around 60,000 Newtons with its jaws, juveniles may have only managed a bite of an estimated 1,200 Newtons. This is still equivalent to an adult lion.

As lead author Andre Rowe, a geology PhD Student from the University of Bristol, argues, without wielding a bite to take down larger herbivores, T. rexes likely hunted weaker animals when younger.

“We presume that they pursued smaller prey and fulfilled an environmental role similar to the ‘raptor’ dinosaurs such as the Dromaeosaurs,” he said. “Adult tyrannosaurs were likely subduing large dinosaurs such as the duckbilled hadrosaurs and Triceratops, which would be quickly killed by their bone-crunching bite.”

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Researchers also found that, if their juvenile slender jaw didn’t grow larger with age, a T. rex could do itself serious harm with each bite. However, they discovered that tension from one of the muscles controlling the mandible (the lower pterygoid muscle) would greatly decrease stresses near the front of the typical adult deep-set tyrannosaur jaw. It’s here where the dinosaur kept its most robust and sharp teeth – and applied the most pressure in its bite.

Despite their fierce reputation, the T. rex doesn’t take the all-time record of the strongest bite on planet Earth. It’s believed that the also-extinct megalodon shark could exert a force of up to 182,200 Newtons with its jaws – that’s over eight times more powerful than today’s Nile alligator.

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Although eventually growing up to 4m in height and 12m in length, T. rexes hatched from their eggs about the size of Chihuahuas. As previous research has indicated, even while not fully-grown, teenage T. rexes may have outcompeted their smaller rivals. This may explain why so few fossils of medium-sized dinosaurs have been found.

Q&A: How did dinosaurs grow so big?

For many animals, there was an intrinsic selective pressure in favour of increasing body size. Since you must share your evolutionary niche with the other members of your species, being slightly larger than your peers helps you eat the higher leaves, catch bigger prey and defend a larger territory. Even more importantly, the larger you are, the safer you are from predators.

Over time, this selective pressure has caused many animal lineages to gradually increase in size. In 2009, scientists in South Africa reported evidence that dinosaurs became larger as they switched from walking on two legs to four.

But being large also means you need more food, can’t escape from natural disasters so easily and reproduce more slowly. As such the fossil record is littered with examples of animals that slowly increased in size before going abruptly extinct.

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