T. rex bite was world's strongest
Tyrannosaurus rex had the most powerful bite of any creature that has ever walked the Earth, say scientists.
Previous estimates of the prehistoric predator's bite suggested it was much more modest - comparable to modern predators such as alligators.
This measurement, based on a laser scan of a T. rex skull, showed that its bite was equivalent to three tonnes - about the weight of an elephant.
The findings are published in the journal Biology Letters.
Dr Karl Bates from the biomechanics laboratory at the University of Liverpool led the research.
He and his colleague, Peter Falkingham from the University of Manchester, used the life-sized copy of a T. rex skeleton exhibited at Manchester Museum as a model for their study. "We digitised the skull with a laser scanner, so we had a 3-D model of the skull on our computer," Dr Bates explained.
"Then we could map the muscles onto that skull."
The scientists then reproduced the full force of a bite by activating the muscles to contract fully - snapping the digital jaws shut.
"Those [simulated] muscles closed the jaw as they would in life and... we measured the force when the teeth hit each other," Dr Bates explained to BBC Nature.
"The maximum forces we found - up at the [back] teeth - were between 30,000 and 60,000 Newtons," he said.
"That's equivalent to a medium-sized elephant sitting on you."
Previous studies had estimated that T. rex's bite had a force of 8,000-13,000 Newtons.Baby bite
The researchers discovered how T. rex's bite force changed as it grew.
'Ultimate' dinosaur predators:
- The massive skull of the Tyrannosaurus rex or "tyrant lizard king" measured 1.5m in length and was balanced by its long, heavy tail. These mighty carnivores may have eaten each other as well as other dinosaurs, research has suggested.
- At 17m long and weighing up to 20 tonnes, Spinosaurus may have been the largest carnivore ever to walk the earth. It lived on a diet of fish, and hunted both in water and on land.
- Predator X is the most powerful marine reptile ever discovered. At 15m long and weighing about 45 tonnes, it was twice as big as most Jurassic ocean predators.
- The gigantic flying vertebrate Hatzegopteryx was a meat-eater that stood as tall as a giraffe and had a wingspan of at least 10m. This predator could walk and hunt on the ground as well as fly.
"Obviously, as its head got a lot bigger, there's an expected increase in bite force associated with that," Dr Bates explained.
But for T. rex, the power behind its bite increased disproportionately - much more than would be expected from a "straightforward linear increase", he said.
This suggests that the predator's diet changed as it matured, and that perhaps only adult T. rex could have punctured the tough hide of another dinosaur.
Dr Bill Sellers, who studies the physical capabilities of living and extinct animals at the University of Manchester, told BBC Nature: "I think everyone expected T. rex to have a strong bite force, but it's even stronger than we expected.
"And it gets stronger as it gets bigger, which is surprising."
He explained that studying dinosaurs shed light on the limits that living things were capable of.
"These animals are extremes - one of the biggest carnivores that ever lived," he said. "So it tells you a lot about the limitations of biology.
"We want to know how organisms work, but living organisms [today] are much smaller. And in terms of mechanics, size is really important."