Tyrannosaurus rex must be the most popular dinosaur in the world, and it’s one of the most studied species in palaeontology. With that comes debate among scientists about the biology and life appearance of this animal. Not long ago there was pondering over whether or not T. rex was exclusively a scavenger, or if it had feathers. Last summer, a paper arguing there were actually several different species of Tyrannosaurus made headlines. Now, the debate over T. rex lips has come to the forefront.
Yes, lips, but not muscular, moveable human-type lips. Some scientists have argued this is the most likely condition for non-bird predatory dinosaurs, including T. rex. Others have suggested these animals had jaws like crocodiles, with tightly-bound skin over the face and jaws from which teeth protruded, visible even when the mouth was closed.
A recent study led by Auburn University palaeontologist Dr. Thomas Cullen has come out in favour of the lipped condition for meat-eating dinosaurs, using T. rex as model species for the study. But it wasn’t as easy as looking for fossilized dinosaur lips.
“We haven't found any oral coverings in dinosaurs because they’re exclusively soft-tissue, and only hard tissues typically preserve in the fossil record,” said Royal B.C. Museum palaeontologist Derek Larson, who co-authored the study.
The authors looked at the wear-and-tear on the surface of T. rex teeth, the relative size of the teeth to the jaws, and the texture of the tooth enamel and jaw bone surface. They compared this data with what’s observed in modern animals like large predatory lizards, which do have lips, and crocodilians, which don’t. It turns out while dinosaurs are more closely related to crocodiles, predatory species were similar to lizards in their oral anatomy.
“We found carnivorous dinosaurs likely had extra-oral coverings (lips),” said Larson. “These would not have been the same as mammal lips, but similar to those seen in lizards and snakes.”
These findings have consequences in how we imagine dinosaurs like T. rex looked and behaved when they were alive. Predatory dinosaurs have long been depicted by artists with teeth protruding from lipless jaws. We now know this probably wasn’t the case.
“Palaeoartists strive to create reconstructions that are as accurate as possible given known information,” said Larson. “We hope we continue to see the gradual increase of extra-oral coverings in dinosaur art.”
"I was surprised at how similar some dinosaur teeth were to monitor lizard teeth,” he said. “For very distantly related groups, their teeth must have functioned virtually identically."
Because dinosaurs are extinct, and mostly what we’re left with is their bones, it doesn’t mean there aren’t ways to learn more about what they looked like and how they lived their lives. It’s hard to say what amazing things we’ll know about dinosaurs in the future, but the possibilities are looking better all the time.
T. rex Trivia:
· T. rex lived at the very end of the Cretaceous Period, making it one of the last non-avian dinosaurs. It lived alongside Triceratops, Ankylosaurus, and Edmontosaurus.
· T. rex is found across western North America, from southern Canada to New Mexico. Two specimens have been found in Alberta so far. One near the town of Huxley and another, nicknamed “Black Beauty”, at Lundbreck Falls. Both can be seen at the Royal Tyrrell Museum of Palaeontology.
· The largest T. rex known to science, nicknamed “Scotty”, was found in Saskatchewan.
· While some have argued T. rex was strictly a scavenger, this is unpopular among palaeontologists. T. rex was almost certainly capable of killing its own food, but probably did scavenge from time to time as well, just like modern carnivores.
· Despite what’s shown in movies, T. rex had excellent eyesight, as well as a powerful sense of smell.
Thomas M. Cullen, et al, Theropod dinosaur facial reconstruction and the importance of soft tissues in paleobiology.Science379, 1348-1352(2023).DOI:10.1126/science.abo7877