(NewsNation) — When you think of a Tyrannosaurus rex, you likely imagine its sharp, giant teeth jutting outside its mouth.

But a new study suggests this picture might not be accurate. Instead, some researchers say the T. rex’s teeth may have been covered by scaly lips.

Authors of the study said the T. rex is usually portrayed with its teeth fully visible because it is being compared to modern crocodiles.

Depictions showing teeth jutting out of dinosaurs’ jaws when closed stem from the idea that the predators’ teeth were too big for their mouths, said study author Thomas Cullen, a paleontologist at Auburn University in Alabama.

Researchers who compared skulls from dinosaurs and living reptiles found a different result. Cullen said some large monitor lizards actually have bigger teeth than the T. rex — though they can still fit them under their own lips.

Scientists also studied wear and tear on tooth surfaces. The Washington Post reports the research team found a T. rex tooth near the Milk River in Alberta,Canada, put it in resin, and sliced it open with a diamond-studded saw to see how it wore down over the dinosaur’s life.

Enamel had worn down evenly on both sides of the tooth — a pattern much different from what is seen on crocodiles. Because enamel is more durable when it stays wet, this led scientists to believe dinosaurs had lips to keep their teeth from wearing down.

Some critics are pushing back on the new theory.

“I don’t find (the new study) persuasive,” Thomas Carr, a vertebrate paleontologist at Carthage College, told Science. Carr and his colleagues wrote their own study that showed that theropods like the T.Rex had highly textured face bones, suggesting that the dinosaur snouts were covered with flat scales and no extra soft tissue, rendering them lipless.

 “I think the day will arrive where somebody will find a fossil mummy of a Tyrannosaur,” Carr said in Science. “But in the meantime, we won’t truly know.”

The Associated Press contributed to this report.