If you ever find yourself staring directly into the jagged, gaping jaws of a hungry Tyrannosaurus rex, take a moment to observe its placid, composed tongue. Remarkably still, no?

Despite what pop culture would have us believe about the wildly elongated, lashing tongues of these marvellous, extinct creatures, new research suggests the towering T. rex and most of its prehistoric dino counterparts were actually rather tongue tied.

An investigation by researchers from the University of Texas at Austin and the Chinese Academy of Sciences has found that while T. rex may have been able to chew you into mincemeat with ease, it wouldn't have been able to stick its tongue out at you beforehand.

Cold comfort perhaps, but why not?

902 t rex dinosaur tongue 2Fossils from Northeast China with delicate hyoid bones (Li et al.)

It's to do with hyoid bones, which help anchor and support the tongue. They're what help you lick – among other kinds of tongue manipulations – but they weren't able to do the same thing for dinosaurs, which is why the stereotypical image of the protruding T. rex tongue has turned out to be massively wrong.

"They've been reconstructed the wrong way for a long time," says vertebrate palaeontologist Julia Clarke from UT Austin.

"In most extinct dinosaurs their tongue bones are very short. And in crocodilians with similarly short hyoid bones, the tongue is totally fixed to the floor of the mouth."

Clarke and fellow researchers discovered this by comparing the hyoid bones of extinct dinosaurs, pterosaurs, and alligators to those of modern birds and alligator specimens.

The analysis revealed most dinosaur hyoid bones resemble those of alligators and crocodiles: relatively short, and because they're connected to the tongue, it means the tongue isn't very mobile.

In contrast, species that evolved later – including bird-like pterosaurs and modern birds – have far more nimble tongues, thanks to greater diversity and length in their hyoid bone shapes.

"Birds, in general, elaborate their tongue structure in remarkable ways," Clarke says. "They are shocking."

As for how these later creatures learned how to move their tongues so effectively while their predecessors couldn't, the team thinks it might have been an evolutionary adaptation that accompanied the growing of wings – or, rather, the losing of arms.

"If you can't use a hand to manipulate prey, the tongue may become much more important to manipulate food," one of the team, Zhiheng Li explains.

"That is one of the hypotheses that we put forward."

It's not the first time Clarke has upturned classical assumptions about these fearsome predators – and particularly what goes on inside their mouths.

Two years ago, she was part of a team that discovered the ferocious, reverberating roars we might expect to emanate from T. rex mouths did not in fact exist. Instead, the animals would have produced soft, cooing noises.

What with the inability to run, and those puny pint-sized arms, these ferocious beasts are getting less scary all the time.

The findings are reported in PLOS ONE.