And the T.Rex has teeth, but you can't see the teeth

The Tyrannosaurus rex's fearsome teeth were probably hidden behind lips. An international research team found no wear on the teeth of theropods, which also includes predatory dinosaurs, as is typical for the exposed teeth of crocodiles, for example. The ratio of skull length to tooth length does not speak against complete coverage of the teeth in predatory dinosaurs, writes the group led by Thomas Cullen from Auburn University (US state of Alabama) in the journal Science.

"Since we started dinosaur restorations in the 19th century, artists have been going back and forth about lips, but lipless dinosaurs became more popular in the 1980s and 1990s," says co-author Mark Witton of the University of England of Portsmouth in a statement from his college. Documentaries and feature films such as "Jurassic Park" would have shaped the image of predatory dinosaurs with exposed teeth. Even paleontologists have so far disagreed on this question.

"Although it has been argued in the past that predatory dinosaur teeth might be too large to be covered by lips, our study shows that in reality their teeth were not unusually large," Cullen points out.

He and his colleagues discovered that the jaws of predatory dinosaurs resemble those of modern-day monitor lizards much more closely than those of crocodiles. This can be seen, for example, in the distribution of openings in the skull bones through which nerves and blood vessels run. And even the mighty Komodo dragon's teeth are completely covered by lips.

The relationship between the length of the skull and the length of the teeth is similar in predatory dinosaurs to that in monitor lizards and therefore at least does not speak against lips in predatory dinosaurs. The most compelling argument, however, comes from the wear patterns of the teeth. In the case of crocodiles, the enamel on the outside of the teeth, which is exposed to the air and other influences, has usually disappeared - in most cases even part of the tooth substance is missing.

Since the enamel of predatory dinosaurs was even thinner than that of modern-day crocodiles, the group argues that without the protection of lips, it should have worn down even faster and more severely. But that is not the case.

In the examined teeth of predatory dinosaurs, the enamel was still present on both sides of the teeth. "Teeth that aren't covered by lips may dry out and become more damaged when eating or fighting, as we see in crocodiles but not in dinosaurs," explains co-author Kirstin Brink of Canada's University of Manitoba in Winnipeg . The authors therefore assume that the dagger-like teeth of T. rex

The results provide new insights into how the soft tissues and appearance of dinosaurs and other extinct species could be reconstructed. The scientists believe this may provide information about how they ate and maintained their dental health, perhaps even other aspects of their evolution and lifestyle. "The results of this study strongly support lip facial reconstructions in theropods, with far-reaching implications for their representation in science and popular culture," write Cullen and colleagues.

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