When Tyrannosaurus rex hunted, it chased down prey, ripped off great hunks of flesh, and then threw back its head to swallow the entire meaty morsel whole. But here's an interesting question: when going in for that bone-crunching bite, just how wide could T. rex fling open its jaws? Thanks to new research coming out of the University of Bristol, we now have an idea. Say ahhh, tyrant king.

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Dr Stephan Lautenschlager from the university's School of Earth Sciences picked out three "beast-footed" (therapod) dinosaurs – a group of two-legged dinosaurs that included the largest carnivores to ever walk the earth – and then used digital models and computer analyses to work out just how far apart the jaws of these ancient predators could stretch. 

“Theropod dinosaurs such a Tyrannosaurus rex ... are often depicted with widely opened jaws, presumably to emphasise their carnivorous nature. Yet, up to now, no studies have actually focused on the relation between jaw musculature, feeding style and the [maximum] possible jaw gape,” says Lautenschlager in a press release.

Aside from the iconic T. rex, Lautenschlager's subjects also included Allosaurus fragilis, another short-armed but smaller carnivore, as well as Erlikosaurus andrewsi, one of a group of strange-looking plant-eaters that sported claws and horny beaks.

As part of the study, the team created detailed digital models based on fossil skulls, and then applied 3D modelling software to help them understand the relationship between muscle strain and jaw gape. "All muscles, including those used for closing and opening the jaw, can only stretch a certain amount before they tear. This considerably limits how wide an animal can open its jaws and therefore how and on what it can feed,” Lautenschlager explains.

So who's got the biggest mouth? It turns out T. rex isn't king here. While both of the hunters, unsurprisingly, were capable of some serious open-wide, Allosaurus took the lead. Its jaws could stretch wider than a right angle, between 79 and 92 degrees. 

While T. rex trails behind at between 64 and 80 degrees, it still wins the day when it comes to more sustained bite force over a wider range of jaw angles – which would have come in handy when crushing bone and dismembering prey.

Of course, both carnivores would have cranked their jaws to the maximum only for supersized meals, staying within a more comfortable range the rest of the time.

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Jaw of T. rex just chilling out (top); jaw of T. rex who wants to kill you (bottom). Image: Stephan Lautenschlager

“We know from living animals that carnivores are usually capable of larger jaw gapes than herbivores, and it is interesting to see that this also appears to be the case in theropod dinosaurs,” says Lautenschlager.

And sure enough, the study's peaceable plant-eater would have had to make do with a 45-degree maximum gape. 

While these results are largely what you'd expect, understanding more about how dinosaur jaws operated does give us a better idea of how they might have hunted, and exactly what they could eat – and how.  

The new research was published in the journal Royal Society Open Science. 


Top header image: Geoff Livingston, Flickr