Jurassic Park may be about to get a makeover. A new study finds that Tyrannosaurus rex and its relatives did not look like crocodiles, with teeth jutting from their maws in all their full, razor-sharp glory. Instead, these dinosaurs covered their chompers with lips, more like today’s lizards.
“This is a nice, concise answer to a question that has been asked for a long time,” says Emily Lessner, a vertebrate paleontologist at Denver Museum of Nature and Science, who was not involved in the new study. But not all experts are convinced.
Both paleontologists and paleoartists have long debated whether theropods—a group of carnivorous dinosaurs that includes T. rex—had lips. Reconstructions by scientists in the 1920s and ’30s showed them with flesh over their teeth, says Thomas Cullen, a paleobiologist at Auburn University. But popular media, including the 1993 movie Jurassic Park, popularized dinos with large, prominent teeth and no lips. “That became … the public perception,” Cullen says. “A big, big theropod with big steak knives sticking out of his mouth.”
To see whether that view had, well, teeth, Cullen and his colleagues analyzed the relationship between skull length and tooth size for living reptiles, such as Komodo dragons—which have lips and are living relatives of theropods—as well as several theropod dinosaurs, like the Velociraptor and T. rex. The team found that theropod teeth weren’t too big or too long for their skulls, similar to living lizards, and thus didn’t have to stick out of their mouths.
Next, the researchers turned to enamel. They compared a slice of tooth from a Daspletosaurus theropod with that of a modern crocodile. The croc tooth had a significantly thinner layer of enamel on its outside (versus the inner side of the teeth that would face the tongue) than the dino tooth, suggesting the dinosaurs likely had lips that protected their teeth from the elements.
Finally, the team looked for clues by comparing various living and dead animals’ skull anatomy. Although birds are the closest living relatives of theropods, they don’t have teeth, so the researchers compared the skull features of iguanas and monitor lizards—both of which have lips—with dinosaurs and crocodiles. Crocs have many little holes all over their snouts, called dome pressure sensor pores, which are part of their sensory system. Lizards and iguanas, however, sport a single row of large holes above their teeth, called foramina, where blood vessels and nerves pass through. Dinosaur skulls much more closely resemble those of the lipped lizards and iguanas, the researchers conclude today in Science, suggesting therapod dinos must also have had lips.
Taken together, the evidence strongly suggests therapods had a kiss that could kill. “There’s little room for any other conclusion,” Lessner says.
Beyond informing artists on how to accurately depict a T. rex. in movies (and Apple TV’s Prehistoric Planet, which showed them lipless), these results are important for researchers who study tooth growth, usage, wear, and pathology, Cullen says. Knowing whether dinos had lips is also key to sussing out their feeding behaviors, he says.
“It’s a great first step,” adds Ashley Morhardt, a paleoneurologist at Washington University School of Medicine in St. Louis. Still, she notes the study is based on a small sample size—only one dino tooth and one croc tooth, for example, which makes it likely biased. “The results are tantalizing,” she says. “But I’m afraid we will need more data to say anything confidently about the dinosaur ‘lip’ debate.”
Thomas Carr, a vertebrate paleontologist at Carthage College, is more dismissive. In 2017, he and his colleagues showed that theropods had highly textured face bones that feel like wrinkled leather, just like crocodiles. This suggested dinosaur snouts were covered with flat scales and had no extra soft tissue, which meant dinos were lipless. “I don’t find [the new study] persuasive,” he says.
To finally settle the debate, researchers will need to find better physical evidence of what therapods actually looked like, Carr says. “I think the day will arrive where somebody will find a fossil mummy of a Tyrannosaur,” he says. “But in the meantime, we won’t truly know.”