Tyrannosaurus rex and its relatives almost certainly had lips, American and Canadian paleontologists have found, challenging the notion that their large teeth were bared.

Auburn University specialists found three types of evidence for their claim: the anatomy of the skull and jaw of theropods - the group of all carnivorous dinosaurs, the wear on their teeth, and the ratio between the size of the teeth and the skull, which point to the existence of structures resembling lips.

"Our study suggests that theropod dinosaurs did not have exposed teeth when the mouth was closed," said paleontologist Thomas Cullen of Auburn University, lead author of the study, published in the journal Science.

"Dinosaur lips differed from mammalian lips in that they covered teeth, but they didn't move on their own—they couldn't retract them when snarling or make any of the movements we associate with lips in humans or other mammals. Dinosaur lips were more similar to those of many lizards or amphibians, even if we associate them with mammals like us," says Cullen.

Tyrannosaurus rex was as intelligent as a primate

They were scaly and are more properly called "labial scales".

In scientific and popular depictions of Tyrannosaurus rex and other carnivorous dinosaurs, they are often bared with crocodile-like teeth.

In fact, their teeth were probably covered by soft facial tissues like most terrestrial reptiles, including Komodo dragons. 

Dinosaur lips offered several advantages - they protected the oral cavity, so the glands, tongue and sensory organs inside were protected.

This is the normal biological condition for terrestrial animals, while living crocodiles deviate from the pattern because they are primarily aquatic or amphibious. 

A study of the relationship between tooth size and skull size refutes the idea that large theropod teeth were too large to be covered by lips.

The study identified large-lipped lizard species with proportionally larger teeth relative to skull size than T. rex.

In crocodilians, the teeth have asymmetric wear on the outside, which is not found in theropods. 

Finally, a study of theropod skulls found evidence of small depressions along the upper jaws that contained nerves and blood vessels to feed the lips and gums. 

"We have a much more realistic interpretation of the facial features of theropods, important for understanding their biology," said Robert Reiss of the University of Toronto, who co-authored the study. 

dinosaurs