New research suggests that even when a tyrannosaurus rex had its mouth closed, its sharp teeth would still be visible. However, it has been discovered that like lizards, if a tyrannosaurus rex had its mouth closed, its teeth would not be visible behind its lips.
According to a report in the journal Science on the 30th of March, researchers from Ohio State University suggest that “dinosaurs, like today’s Komodo dragons, probably had tissue around their mouths that acted as lips.”
The researchers analyzed fossils of living reptiles and dinosaur skulls. They examined the patterns of small holes in the upper jawbone, which connect blood vessels and nerves to the tissue surrounding the mouth.
In the case of crocodiles, which lack lips, these holes were scattered throughout the entire jawbone. However, in reptiles with lips, such as lizards, the small holes were arranged in a row along the edge of the jawbone closest to the teeth. Analysis suggests that the tyrannosaurus rex had a similar pattern of hole arrangements to that of lizards.
Evidence was also found in the enamel of the teeth, the outermost layer of the tooth. The thicker the enamel, the more easily it wears down. Crocodiles have thick enamel and live in water, which helps them maintain moisture, but they also have more cracks on the exposed surface.
On the other hand, dinosaurs, such as the tyrannosaurus rex, have thin enamel covering their teeth and exhibit a uniform wear pattern. This suggests that dinosaurs had lips that protected their teeth and covered their saliva.
The “Hesperosuchus”, a cousin of extinct crocodiles, was found to have neat hole arrangements in its jawbone. This indicates that early reptiles that gave rise to both dinosaurs and crocodiles may have had lips. The researchers estimate that lips may have disappeared from the crocodile lineage that has survived to the present day.