“This study is a great piece of paleontological forensic detective work,” says University of Edinburgh palaeontologist Steve Brusatte, who was not involved in the new research.
Their overall analysis suggested T. rex and similar dinosaurs did not have extra long teeth for their size: A set of lips could have easily covered their teeth. More telling is that the enamel of dinosaur teeth is relatively thin, and would have been prone to drying out if constantly exposed to the air. Lips would have kept their teeth wet and functional, something that crocodiles don’t have to worry about as aquatic animals.
“Cullen and colleagues make an excellent case for the presence of extra-oral tissues in non-avian theropods,” says University of Pennsylvania palaeontologist Ali Nabavizadeh, who was not involved in the new study.
Lips may not be unique to theropods, either. Recent studies on various herbivorous dinosaurs, such as the long-necked sauropods and horned ceratopsids, have found evidence of gums, cheeks, and other soft tissues covering their teeth.
And for those who might suggest that the change makes dinosaurs less impressive, Cullen notes that “having lips, or even feathers, has no real bearing on something being scary or fearsome”—just look at birds of prey or many mammalian carnivores.
Adding lips to T. rex and other dinosaurs creatures a fuller image of their anatomy and how they interacted with their environments, the scientists say.
“I’m very interested in the role soft tissues play when interpreting tooth pathologies,” Brink says, as gums, lips, and other tissues could experience many of the same injuries and diseases that affect living animals.
Nabavizdeh adds that lips likely made T. rex a more effective predator.
For one, reptiles don’t have the lip muscles that mammals do, so a T. rex couldn’t sneer (or do an Elvis Presley impression, for that matter). The lips, Nabavizdeh notes, were to protect the teeth from abrasion and to keep them wet.
Think of their lips as akin to the sheath on a knife, Brusatte adds, something that “helped maintain the murder weapons and ensued they were as deadly as possible.”