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Close your eyes and imagine a Tyrannosaurus rex.

Your dinosaur probably has a hulking frame, scaly skin, puny arms and protruding teeth it wielded to be the apex predator of its era. Right?

If so, sorry: Your image of a T. rex with a big, fierce grin with bare teeth may be wrong. The oversized dagger teeth of the T. rex and its relatives were probably completely covered by thin, scaly “lips,” according to a new study that aims to crack the image of the carnivore popularized by the film “Jurassic Park.”

For decades, many paleontologists and artists alike depicted the T. rex family with lipless mouths, similar to modern-day crocodiles. For illustrators and movie makers, the bare teeth gave their creations a fierce edge. For fossil hunters, the teeth they found in the ground simply seemed too big to be covered by lips.

But now an international team of scientists is challenging some of the best-known depictions of dinosaurs in television and movies. Instead, these researchers say, the T. rex looked more like a lizard, with scaly lips covering and sealing their mouths when closed.

“There were lots of monster movies with toothy dinosaurs,” said Robert Reisz, a paleontologist at the University of Toronto Mississauga who co-wrote the paper published Thursday in the journal Science. But it was the 1990s “Jurassic Park,” he said, “that made me groan and moan about the multitude of errors and inaccuracies that started us talking about this issue.”

Dean Mouhtaropoulos

With lips, the T. rex family bears more of a resemblance to Barney, the purple dinosaur from the PBS children’s show.

The research underscores how dramatically our conceptions of how dinosaurs looked and acted have changed over time as scientists dig up new evidence.

Yet the specific suggestion of a lipped T. rex is poised to spark a debate as ferocious as the dinosaur itself, with other paleontologists pointing to fossil evidence suggesting these carnivores indeed had the bare teeth seen in the movies.

“Completely unconvincing,” Thomas Carr, a paleontologist at Carthage College in Wisconsin whose own work suggests lipless tyrannosaurs, said of the latest study.

Reconstructing what prehistoric creatures look like is never easy. With skin, muscles and other soft tissue having rotted away ages ago, it is up to so-called “paleoartists” to, quite literally, mix art with science and infer what ancient animals looked like based mainly on the bones left over.

But paleontologists’ interpretation of bones has changed over time.  Some of the first depictions of dinosaurs showed them as sluggish, swamp-bound beasts, too big to leave the water for long. Others portrayed dinosaurs like dragons or other mythical medieval creatures.

“People project their fantasies of awesome and scary creatures onto these skeletons,” paleoartist C. M. Kosemen said.

Image  by Mark P. Witton

Only later did paleontologists begin depicting dinosaurs as mobile and upright, like birds — the closest living relatives of the extinct reptiles. (So closely related, in fact, that birds aren’t just related to dinosaurs — birds are, scientifically speaking, true dinosaurs.)

Many old illustrators drew dinosaurs with lips, according to Mark P. Witton, a paleontologist and palaeoartist at the University of Portsmouth in England who also co-wrote the paper. But in the 1980s, the realization that ancient dinosaurs are related to birds and crocodiles led many paleoartists to begin omitting lips from the dinosaurs they drew.

Then, in 1993, Steven Spielberg’s “Jurassic Park” hit theaters. The movie’s iconic T. rex cemented the popular image of the predator with bare teeth, even when its massive mouth was closed.

“What really blows the door open and lets all the lipless dinosaurs in is ‘Jurassic Park,’” Witton said. “The ‘Jurassic Park’ T. rex was so iconic and so influential that from that moment on, that’s what pop culture dinosaurs start to look like.”

To figure out whether the actual tyrannosaur lineage had lips or not, the research team turned to a tooth found near the Milk River in Alberta.

Plucked from the jaw of a Daspletosaurus, a close relative of the T. rex, the fossilized tooth was embedded in resin and sliced open with a diamond-studded saw to see how it had worn down over the dinosaur’s life.

Sawing open an irreplaceable fossil by hand is a high-stress job. “I didn’t enjoy it, but I’ve done that a bunch with a bunch of other specimens,” said Thomas Cullen, an Auburn University paleontologist and study co-author. “So I was tapped to do that part.”

The research team saw that the enamel had worn down evenly on both sides of the tooth, a pattern markedly different from the wear seen on crocodile chompers and one that suggests the dinosaurs had lips to protect their teeth. Enamel is more durable when it stays wet.

Mustafa Ozer

Steve Finn

The team also found the teeth of T. rex and related dinosaurs were, relative to skull size, no larger than those in modern lizards with lips, suggesting the dinosaur’s pearly whites were not too big for lips to cover them. The team also found the distribution of small holes in the jaws for nerves and blood vessels connected to tissue around the  mouth were more similar to that of lizards than crocodiles.

Whatever their appearance, these dinosaur lips were likely to have lacked muscles, meaning a T. rex wouldn’t be able to snarl and smile like humans and other mammals.

When reconstructing a prehistoric animal, “the closest relatives are usually an okay model,” Cullen said. But birds don’t have teeth at all, making them a poor point of comparison. And crocodiles are built for swimming and sensing movements in water. The better comparison, the researchers say, are modern lizards with lips, like the Komodo dragon.

“This is one of those exceptions to the rule, if you want, in that the two closest relatives to the dinosaurs today, birds and crocodilians, are both very specialized compared to their ancestral appearance,” he added.

But Julien Benoit, a paleontologist at the University of the Witwatersrand who was not involved with the study, said he wants to see more fossilized teeth examined before coming to a conclusion. “This paper provides further evidence in favor of lips, but does not settle the debate,” he said.

And Carr, the Carthage College paleontologist also unaffiliated with the latest research, said he and his colleagues concluded in <a href="https://www.nature.com/articles/srep44942" target=_blank>their own 2017 paper</a> the T. rex family had no lips based on a wrinkle pattern on the skull that corresponds with scaly skin.

“That wrinkly texture is also seen in crocodiles,” Carr said. “That texture in both crocs and tyrannosaurs goes all the way down to the edge of the mouth in the upper and lower jaws. And so that is decisive.”

But Cullen, one of the new study’s co-authors, said there is no strong evidence in the skulls of living animals that the wrinkle pattern precludes the presence of lips. “Simply put, the wrinkled texture along the upper jaws,” he said, “does not appear to be strongly correlated to lips one way or another.”

Carr is confident the debate will be settled someday. “What we need is a fossil of a mummy tyrannosaur that preserves the integument of the face,” he said.

Fossil hunters have found mummified soft tissue of other dinosaurs before. So for the T. rex family, “there’s good reason to think that that day will arrive,” he said.

This article is part of Animalia, a column exploring the strange and fascinating world of animals and the ways in which we appreciate, imperil and depend on them.

Columbia University, BA in economics and political science

Columbia University, MA in science journalism

Dino Grandoni is a reporter covering wildlife, biodiversity and other climate and environmental issues. He is the author of Animalia, a column exploring the strange and fascinating world of animals.

Dino Grandoni

T. rex’s big, bare teeth? They may be a myth, study says

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The Washington Post illustration; Roslan Rahman/AFP via Getty Images, iStock

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Scientists say your idea of how the T. rex looked is probably wrong