Tyrannosaurus rex and velociraptor may have had lips covering their teeth, new study finds

An international team of paleontologists has found evidence that may change the modern understandings of the Tyrannosaurus rex and velociraptor.

A paper published in the journal Science released on Thursday says new evidence suggests that instead of large, exposed teeth, the dinosaur species actually had lips enclosing their mouths.

This discovery is a significant step in uncovering a more accurate picture of creatures that lived more than 66 million years ago and could change reconstructions and depictions of dinosaurs in the future, according to experts in the field.

Derek Larson, a co-author of the paper and a paleontologist at the Royal B.C. Museum, said that the dinosaurs' lips were not the "kissing lips" seen on mammals today. They were likely less dexterous and more similar to the lips of modern lizards.

For a long time, theropod dinosaurs such as the T. rex were considered to have exposed teeth, similar to modern crocodiles, thought to be too large to be contained behind the lips. 

Gavin Bradley, a paleontologist from the University of Alberta who isn't involved with the paper, said that they were considered to have exposed teeth — similar to one of their closest living relatives, the modern crocodile. 

"When we were trying to reconstruct the physiology or behaviour of dinosaurs, we often looked at their closest living relatives, so that would be crocodiles or birds…but crocodiles don't have lips," he said.

This has influenced popular depictions of the T. rex in artist renderings and films, including Jurassic Park, said Thomas Cullen, the study's lead author and an assistant professor at Auburn University in Alabama.

"I think this is another piece in that puzzle of getting people to think of these animals as just that, as animals and not necessarily as movie monsters," he said.

Cullen says he first began looking into evidence of lips on theropods about a decade ago when he worked at the University of Toronto, alongside other paleontologists, including Larson, at the university and Royal Ontario Museum. It started as a side project, born from speculation about whether it was possible to prove the existence of parts of dinosaurs — such as lips — that may have been lost to time.

"The soft tissues have all decayed away, so we are left with indirect forms of evidence," said Larson.

In their search for evidence of lips, the researchers took two approaches: examining the wear patterns on T. rex tooth enamel and comparing its jaw and tooth proportions to modern lizards.

They found that the T. rex had equal tooth enamel thickness, which was more consistent with teeth that are constantly hydrated inside a mouth than the uneven enamel on exposed crocodile teeth.

When comparing the tooth and skull proportions to modern monitor lizards, the team also discovered that the T. rex had typically sized teeth for a predator of its size — and some modern lizards with lips actually had larger teeth compared to their skull size.