Edmontosaurus, a juvenile, disappears into the enormous, lipped mouth of Tyrannosaurus. Credit: Mark Witton
Researchers challenged the idea that predatory dinosaurs like Tyrannosaurus rex had exposed teeth, suggesting that they had scaly, lizard-like lips rather. Theropod mouth anatomy resembled lizards more than crocodiles, according to the findings.
Tyrannosaurus rex, a predatory dinosaur species described in Jurassic Park, did not have permanently exposed teeth, rather scaly, lizard-like lips covering and sealing their faces, according to a new study.
Theropod dinosaurs, a group of two-legged dinosaurs that includes carnivores and top predators such as T. rex and Velociraptor, as well as birds, had permanently visible upper teeth that hung over their lower jaws, similar to the mouth of a crocodile.
Reconstructions of the T. rex skull and head
A group of researchers in the United States has challenged some of the most well-known depictions, claiming that these dinosaurs had lips similar to those of lizards and their relative, the tuatara — a rare reptile found only in New Zealand, which are the last survivors of a species that flourished during the dinosaur age.
Theropod jaw anatomy and function resembled that of lizards more than crocodiles in the most thorough examination of this issue yet.
Reptile lips cover their teeth but cannot be retracted or retracted from a snarl, unlike in humans or other mammals.
Derek Larson, study co-author of The Royal BC Museum in Canada's Collections Manager and Researcher in Palaeontology, said: "In the case of dinosaurs, their closest relatives have been evolutionarily distinct for hundreds of millions of years and are today extremely special.
"It's astonishing how similar theropod teeth are to monitor lizards. From the smallest dwarf monitor to the Komodo dragon, the teeth function in much the same way."
Tyrannosaurus rex is bellowing with its mouth shut, like a vocalising alligator. With its mouth closed, all of T. rex's massive teeth would be hidden behind its lips.
“Dinosaur artists have gone back and forth on lips since we began restoring dinosaurs in the 19th century, but lipless dinosaurs became more prominent in the 1980s and 1990s. They became deeply rooted in popular culture through films and documentaries — Jurassic Park and its sequels, Walking with Dinosaurs, etc.
"This shift in trend was likely sparked by a preference for a different, violent appearance rather than a shift in scientific reasoning." We're altering some of our favourite dinosaur pictures, such as the iconic Jurassic Park T. rex."
The findings, published in the journal Science, revealed that tooth wear in lipless animals was significantly different from that seen in carnivorous dinosaurs, and that dinosaur teeth were no larger, relative to skull size, than those of modern lizards, suggesting that they were not too big to cover with lips.
Mark Witton takes a half-grown Tyrannosaurus, who has a whole set of teeth, down Struthiomimus, a beaked ostrich dinosaur.
The distribution of tiny holes around the jaws, which supply nerves and blood to the gums and tissues around the mouth, were more lizard-like in dinosaurs than crocodile-like. Furthermore, modelling mouth closure of lipless theropod jaws showed that the lower jaw either had to crush jaw supports or disarticulate the jaw joint to seal the mouth.
"Speech is vital to maintaining the health of your teeth," says the co-author Kirstin Brink, a University of Manitoba assistant professor of paleontology.
"Dinosaur teeth have very thin enamel, and mammal teeth have thick enamel (with some exceptions). Crocodile enamel is a bit thinner than dinosaur enamel, but not as thick as mammalian enamel."
Mark Witton's one-sheet report on the main investigations and conclusions of the study
“Despite the fact that predatory dinosaur teeth may be too big to be covered with lips, our research demonstrates that, in fact, their teeth were not atypically large.”
The findings provide new insights into how dinosaurs and other extinct animals' soft tissues and appearance are rebuilt. This may reveal vital information about how they ate, how they maintained their dental health, and the wider patterns of their evolution and ecology.
"Some believe that we're clueless about dinosaur appearance beyond basic features like the number of fingers and toes," said Dr Witton. "We now know that we're not being clueless, but we're at a point where we can say "oh, that doesn't have lips?" Or "a certain sort of scale or feather?" Or "a tiger without stripes."
The researchers say that their research does not claim that extinct animals had exposed teeth — some, such as sabre-toothed carnivorous mammals, or marine reptiles and flying reptiles with extremely long, interlocking teeth, did.
T. rex's Deadly Teeth Were Hidden Behind Scaly Lips for More Information
Thomas M. Cullen, Derek W. Larson, Diane Scott, Tea Maho, Kirstin S. Brink, David C. Evans, and Robert Reisz, "Theropod dinosaur facial reconstruction and the importance of soft tissues in paleobiology," Science. DOI: 10.126/science.abo7877
