Did Tyrannosaurs Have Lips Like Lizards
Tyrannosaurs may have used lips similar to those of modern lizards, a finding highlighted by researchers at the University of Portsmouth. The big question in paleontology has long centered on whether theropod dinosaurs, the group that includes fearsome predators like Tyrannosaurus rex and Velociraptor, carried mouths without lips. If lips were absent, the upper teeth would likely sit over the lower jaw in a way that mirrors the mouth structure seen in modern crocodiles. Yet soft tissues leave little imprint in the fossil record, making direct evidence scarce and interpretations challenging.
To shed light on this issue, Derek Larson and his team conducted a detailed analysis of fossil remains to understand how dinosaur mouths were arranged and functioned. The researchers compared the teeth, wear patterns, and the overall jaw morphology of theropods with other reptile groups described as liped and labile. Their findings point to a closer resemblance between theropod mouths and the jaws of lizards than to those of crocodiles. The results indicate that dinosaurs possessed lizard-like oral tissues, including scaly lips that would have concealed their teeth when the mouth was closed.
According to the study, the similarity between theropod teeth and those of monitor lizards is striking. This includes both the tooth shape and how the teeth interact with the gums and surrounding tissues during feeding. In short, the jaw function observed in monitor lizards provides a better model for understanding theropod mouths than does the crocodile mouth architecture. The researchers emphasize that such comparisons help explain how bite mechanics worked across different reptile lineages, even when the animals are not closely related.
In further support of the lip hypothesis, the study notes several key observations. The wear patterns on theropod teeth align with a lip-covered arrangement, and the teeth were small enough to be tucked beneath the lips when the mouth closed. The jaw anatomy also showed tiny openings that supplied nerves and blood to the gums and surrounding mouth tissues, a feature that appears more characteristic of dinosaurs than crocodiles. When simulations tested lipless theropod jaws closing, the biomechanics suggested that the jawbone would experience forces that could crush supportive structures or even disrupt the jaw joint. These biomechanical insights reinforce the idea that theropods likely had lips that shielded and concealed their teeth, much like modern lizards. — study authors