T. Rex Had Lips That Concealed Its Teeth, Study Says

Paleontologists say popular, toothy depictions of the dinosaur may have missed the mark

A T. rex with lips consumes a smaller dinosaur
The Tyrannosaurus rex may have had lips. Mark Witton

Contrary to popular depictions of the king of dinosaurs—with razor-sharp fangs protruding from its jaw—a new study suggests the Tyrannosaurus rex’s fearsome teeth were hidden behind lizard-like lips.

While some critics are pushing back against this idea, the paper, published Thursday in the journal Science, proposes a change in how the world sees T. rex. It might be time to shift the toothy imagining of the dinosaur that filmmakers have picked up on, leading to blockbuster movies like Jurassic Park.

“There were lots of monster movies with toothy dinosaurs,” Robert Reisz, a paleontologist at the University of Toronto Mississauga who co-wrote the paper, tells Dino Grandoni of the Washington Post. But the Jurassic Park series specifically made him “groan and moan about the multitude of errors and inaccuracies that started us talking about this issue.”

Before this study, scientists thought the T. rex had a mouth similar to a crocodile’s, in which the teeth are visible even when the jaw is shut. Given the close relation between the reptiles, this hypothesis made sense. Furthermore, many paleontologists believed that T. rex teeth were simply too large not to poke out of the dinosaurs’ mouths—some Tyrannosaurus teeth might have been longer than six inches, per the Wall Street Journal’s Aylin Woodward.

However, a tooth from a Daspletosaurus, a T. rex relative, provided a key piece of evidence in support of lips. The scientists embedded the tooth in resin and used a diamond-studded saw to slice into it—an incredibly stressful job, per the Post. They realized that the tooth’s enamel lacked significant wear—had the dinosaur’s tooth been exposed to dry air in a lip-free mouth, its enamel would have been more degraded, scientists say.

After all, crocodilian teeth suffer lots of damage due to their lack of protection from lip-like tissue. An American alligator may go through some 3,000 teeth in its lifetime, but the T. rex required about two years to replace just one tooth. This suggests the large dinosaurs needed lips to preserve their fangs, researchers say.

Additionally, the team compared skull lengths and tooth sizes of more than 20 fossilized theropod dinosaurs and several other lizard species. They found that, like the Komodo dragon, the T. rex could seemingly fit its chompers behind a lipped mouth.

Four artistic representations of a T. rex head
By comparing skull lengths and tooth sizes of various dinosaurs and other reptiles, scientists found that the T. rex could likely have fit its teeth behind a lipped mouth. Mark Witton

“We’ve really put some new data on the table that I think makes it now pretty indefensible to have the goofy-looking theropods with their teeth hanging out,” says co-author Mark Witton, a paleontologist and paleoartist from the University of Portsmouth, to the Wall Street Journal. “It is time that we have a big shake-up of what we think these dinosaurs looked like in wider culture.”

While this study challenges media portrayals of the T. rex’s toothy grin, this is not the first time that cultural imaginings of the behemoth have changed with new scientific discoveries. In the past several years, paleontologists proposed that the king of dinosaurs could not run and had a larger tail than previously thought.

Despite the new findings, some critics remain unconvinced.

“I don’t find [the new study] persuasive,” says Thomas Carr, a vertebrate paleontologist at Carthage College, to Science’s Rodrigo Pérez Ortega. In 2017, Carr and his colleagues published a paper suggesting that theropods like the T. rex had face bones with the texture of wrinkled leather, like crocodiles do. This would mean that dinosaur snouts were scaly and lipless.

Regardless, scientists agree that discovering a fossil mummy, which has the skin intact, would settle this debate. Such a find could offer better physical evidence as to what the mouths of theropods looked like.

This is not a far-reaching hope—scientists have already found mummified fossils of other dinosaurs. With this in mind, “there’s good reason to think that that day will arrive,” Carr tells the Post.

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