A new study published in the journal Science has found that predatory dinosaurs, such as the Tyrannosaurus rex, did not have permanently exposed teeth as previously thought. Instead, they had scaly, lizard-like lips that covered and sealed their mouths.

The findings challenge the best-known depictions of theropod dinosaurs, the group of two-legged dinosaurs that includes top predators like T. rex. The research examined lipped and lipless reptile groups’ teeth structure, wear patterns, and jaw morphology.