An Auburn University professor, in collaboration with an international team of researchers, has determined that theropod dinosaurs, like the famed Tyrannosaurus rex that once roamed what is now the northwest United States, had lips. Theropods are the group of bipedal dinosaurs that include the T-rex and velociraptor and many birds. The theropod dinosaurs' lips covered their teeth, but weren't like those of mammals, whose lips possess a complex musculature and can move independently and turn up a snarl or purse to peck a cheek.
Thomas Cullen, an assistant professor in the College of Sciences and Mathematics' Department of Geosciences at Auburn University, was part of an international team of researchers who published their findings recently on science.org. The biggest takeaway is that the teeth of dinosaurs like the T-rex and velociraptor were not visible when their mouths were closed, according to the research conducted by the team. "We reconstructed soft tissue anatomy, compared dental measurements and studied dental health and wear records to further uncover that what you are used to seeing on the big screen is not accurate,” Cullen said. “The teeth of these theropod dinosaurs did not experience wear and tear like a crocodile, and most likely had a lip-like covering."
Cullen further explained why dinosaur lips weren't likely to be turned into a logo for the Rolling Stones or be good candidates for lipstick hellos on a mirror. "Dinosaur lips would be different from mammal lips in that they would cover the teeth, but could not be moved independently, couldn’t be curled back into a snarl, or make other sorts of movements we associate with lips in humans (or other mammals)," he said. "In this way, dinosaur lips would be more similar to those of many lizards or amphibians, even if we typically associate the structure with mammals like ourselves."
"Tyrannosaurus might have had lips, but they weren’t for kissing for reasons related to their underlying anatomy and also just good common sense,” said University of Portsmouth's Mark Witton, who was part of the team of researchers. The team of researchers compared multiple aspects of the paleobiology of theropod dinosaurs to reach their conclusions, including:
• Tooth wear The amount of wear on the actual enamel and dentine of their teeth showed less wear than those of their closest living relatives, the crocodile;
• Size and scale The size of the skull in approximation to the jaw and teeth prove they could have had lips, and their teeth would not be too large to be covered;
• Bone anatomy The surface features of the bone around the teeth are much more similar to lizards than crocodiles, including the possession of a line of small pits which house blood vessels and nerves for their oral skin and gums.
“It’s quite remarkable how similar theropod teeth are to monitor lizards," said Derek Larson, collections manager at the Royal BC Museum. "From the smallest dwarf monitor to the Komodo dragon, the teeth function in much the same way. So, monitors can be compared quite favorably with extinct animals like theropod dinosaurs based on this similarity of function, even though they are not closely related.” Against the backdrop of the image of dinosaurs like the T-rex that were popularized in films like "Jurassic Park," Witton addressed how far research and understanding of dinosaurs and their appearance has come.
“A major factor is fashion! Dinosaur artists have gone back and forth on lips since we started restoring dinosaurs during the 19th century, but lipless dinosaurs became more prominent in the 1980s and 1990s. They were then deeply rooted in popular culture through films and documentaries — Jurassic Park and its sequels, Walking with Dinosaurs and so on. Curiously, there was never a dedicated study or discovery instigating this change and, to a large extent, it probably reflected preference for a new, ferocious-looking aesthetic rather than a shift in scientific thinking," he said. "Some take the view that we’re clueless about the appearance of dinosaurs beyond features as basic as the number of fingers and toes.
"But our study and others like it show that we have an increasing good handle on many aspects of dinosaur appearance. Far from being clueless, we’re now at a point where we can say 'oh, that doesn’t have lips? Or a certain type of scale or feather? Then that’s as realistic a depiction of that species as a tiger without stripes.'" Cullen conducted many of the analyses while he was a post-doctoral student at the Field Museum of Natural History in Chicago.
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