T-rex and other therapods hid their teeth beneath thin lips, contradicting literature

The enamel of the teeth of theropods is known to be relatively thin. Continual exposure is believed to probably cause harmful tooth desiccation and wear since giant theropod species likely preserved their pointed, serrated teeth for extended periods.

Uncertainty exists on whether the teeth of these extinct apex predators were permanently exposed, as is sometimes shown, or covered by scales that resembled lips, similar to Komodo dragons. Thomas Cullen and the team examined the correlation between skull length and tooth size for various theropod dinosaurs and contemporary and extinct toothed reptiles to explore alternative hypotheses of theropod face reconstructions.

A comparative histological investigation

They conducted a comparative histological investigation of crocodilian and tyrannosaurid tooth wear patterns. The researchers claim that theropod teeth showed no signs of outer surface wear in contrast to their closest-toothed crocodilian cousins, indicating the presence of extraoral tissues and oral secretions necessary to keep them hydrated and protected from exposure.

In addition, the scientists discovered that the tooth-skull size relationship in theropods closely matched that of current reptiles, notably monitor lizards, who do not have exposed teeth, despite certain theropods having much larger skulls and teeth than extant reptiles.

According to these discoveries, theropod teeth were not too large to fit inside their mouths without being revealed. These findings may also impact how dinosaurs are portrayed in science and popular culture.

The study was published in Science on March 30.