A juvenile Edmontosaurus disappears into the enormous, lipped mouth of Tyrannosaurus. Credit: Mark Witton
A recent study challenges the depiction of predatory dinosaurs like Tyrannosaurus rex with exposed teeth, suggesting they had scaly, lizard-like lips instead. By examining tooth structure, wear patterns, and jaw morphology of reptile groups, researchers concluded that theropod mouth anatomy resembles lizards more than crocodiles. The findings imply that many popular dinosaur depictions, including the iconic JurassicThe Jurassic period is a geologic time period and system that spanned 56 million years from the end of the Triassic Period about 201.3 million years ago to the beginning of the Cretaceous Period 145 million years ago. It constitutes the middle period of the Mesozoic Era and is divided into three epochs: Early, Middle, and Late. The name "Jurassic" was given to the period by geologists in the early 19th century based on the rock formations found in the Jura Mountains, which were formed during the Jurassic period.” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]”>Jurassic Park T. rex, are incorrect. This research provides valuable insights into the appearance, feeding habits, dental health, and evolutionary patterns of dinosaurs and other extinct speciesA species is a group of living organisms that share a set of common characteristics and are able to breed and produce fertile offspring. The concept of a species is important in biology as it is used to classify and organize the diversity of life. There are different ways to define a species, but the most widely accepted one is the biological species concept, which defines a species as a group of organisms that can interbreed and produce viable offspring in nature. This definition is widely used in evolutionary biology and ecology to identify and classify living organisms.” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]”>species.
A new study suggests that predatory dinosaurs, such as Tyrannosaurus rex, did not have permanently exposed teeth as depicted in films such as Jurassic Park, but instead had scaly, lizard-like lips covering and sealing their mouths.
Researchers and artists have debated whether theropod dinosaurs, the group of two-legged dinosaurs that includes carnivores and top predators like T. rex and Velociraptor, as well as birds, had lipless mouths where perpetually visible upper teeth hung over their lower jaws, similar to the mouth of a crocodile.
T. rex skull and head reconstructions. Credit: Mark Witton
However, an international team of researchers challenge some of the best-known depictions, and say 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 an order of reptiles that thrived in the age of the dinosaurs.
In the most detailed study of this issue yet, the researchers examined the tooth structure, wear patterns and jaw morphology of lipped and lipless reptile groups and found that theropod mouth anatomy and functionality resembles that of lizards more than crocodiles. This implies lizard-like oral tissues, including scaly lips covering their teeth.
These lips were probably not muscular, like they are in mammals. Most reptile lips cover their teeth but cannot be moved independently – they cannot be curled back into a snarl, or make other sorts of movements we associate with lips in humans or other mammals.
Study co-author Derek Larson, Collections Manager and Researcher in Palaeontology at the Royal BC Museum in Canada, said: “Palaeontologists often like to compare extinct animals to their closest living relatives, but in the case of dinosaurs, their closest relatives have been evolutionarily distinct for hundreds of millions of years and today are incredibly specialised.
“It’s quite remarkable 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. So, monitors can be compared quite favourably with extinct animals like theropod dinosaurs based on this similarity of function, even though they are not closely related.”
Tyrannosaurus rex bellowing with its mouth shut, like a vocalising alligator. With its mouth closed, all of the enormous teeth of T. rex would be invisible behind its lips. Credit: Mark Witton
Co-author Dr Mark Witton from the University of PortsmouthEstablished in 1992, the University of Portsmouth is a public university in the city of Portsmouth, Hampshire, England. Prior to reaching university status, the school was known as Portsmouth Polytechnic from 1969 until 1992 and can trace its history back to 1870 as the Portsmouth and Gosport School of Science and Art.” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]”>University of Portsmouth said: “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. We’re upending this popular depiction by covering their teeth with lizard-like lips. This means a lot of our favourite dinosaur depictions are incorrect, including the iconic Jurassic Park T. rex.”
The results, published in the journal Science, found that tooth wear in lipless animals was markedly different from that seen in carnivorous dinosaurs and that dinosaur teeth were no larger, relative to skull size, than those of modern lizards, implying they were not too big to cover with lips.
A half-grown Tyrannosaurus, sporting a full set of lips, runs down Struthiomimus, a beaked ostrich dinosaur. Credit: Mark Witton
Also, the distribution of small 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-supporting bones or disarticulate the jaw joint to seal the mouth.
“As any dentist will tell you, saliva is important for maintaining the health of your teeth. Teeth that are not covered by lips risk drying out and can be subject to more damage during feeding or fighting, as we see in crocodiles, but not in dinosaurs,” said co-author Kirstin Brink, Assistant Professor of Palaeontology at the University of Manitoba.
She added: “Dinosaur teeth have very thin enamel and mammal teeth have thick enamel (with some exceptions). Crocodile enamel is a bit thicker than dinosaur enamel, but not as thick as mammalian enamel. There are some mammal groups that do have exposed enamel, but their enamel is modified to withstand exposure.”
A one-sheet summary of the main investigations and conclusions of the study. Credit: Mark Witton
Thomas Cullen, Assistant Professor of Paleobiology at Auburn University and study lead author, said: “Although it’s been argued in the past that the teeth of predatory dinosaurs might be too big to be covered by lips, our study shows that, in actuality, their teeth were not atypically large. Even the giant teeth of tyrannosaurs are proportionally similar in size to those of living predatory lizards when compared for skull size, rejecting the idea that their teeth were too big to cover with lips.”
The results provide new insights into how we reconstruct the soft tissues and appearance of dinosaurs and other extinct species. This can give crucial information on how they fed, how they maintained their dental health, and the broader patterns of their evolution and ecology.
Dr Witton said: “Some take the view that we’re clueless about the appearance of dinosaurs beyond basic features like the number of fingers and toes. But our study, and others like it, show that we have an increasingly 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.”
The researchers point out that their study doesn’t say that no extinct animals had exposed teeth — some, like sabre-toothed carnivorous mammals, or marine reptiles and flying reptiles with extremely long, interlocking teeth, almost certainly did.
For more on this research, see Deadly Teeth of T. rex Were Hidden Behind Scaly Lips.
Reference: “Theropod dinosaur facial reconstruction and the importance of soft tissues in paleobiology” by Thomas M. Cullen, Derek W. Larson, Mark P. Witton, Diane Scott, Tea Maho, Kirstin S. Brink, David C. Evans and Robert Reisz, 30 March 2023, Science.
DOI: 10.1126/science.abo7877
Source: SciTechDaily
