New study challenges depiction of predatory dinosaurs with exposed teeth, suggesting they had scaly lips covering their mouths like lizards

A recent study challenges the popular portrayal of predatory dinosaurs, such as the mighty Tyrannosaurus rex, as having permanently exposed teeth. Contrary to depictions in movies like Jurassic Park, researchers now suggest that these dinosaurs had scaly, lizard-like lips that covered and sealed their mouths.

For years, there has been a debate among researchers and artists about whether theropod dinosaurs, a group of two-legged dinosaurs that includes carnivores and top predators like T. rex and Velociraptor, as well as birds, had lipless mouths where their upper teeth were always visible and hung over their lower jaws, similar to the mouth of a crocodile.

However, an international team of researchers now challenges these popular depictions and argues that these dinosaurs had lips similar to those of lizards and their relative, the tuatara – a rare reptile found only in New Zealand, which is the last surviving member of an order of reptiles that thrived in the age of the dinosaurs.

In the most comprehensive study of its kind, the researchers examined the tooth structure, wear patterns, and jaw morphology of lipped and lipless reptile groups. They found that the mouth anatomy and functionality of theropods resembled that of lizards more than crocodiles, suggesting that these dinosaurs likely had scaly lips covering their teeth.

A one-sheet summary of the main investigations and conclusions of the study. Credit: Mark Witton

The researchers suggest that the lips of these dinosaurs were not muscular, unlike those of mammals. Reptile lips typically cover their teeth, but they cannot move independently and make various movements that we associate with lips in humans or other mammals.

Derek Larson, a co-author of the study and a researcher in at the Royal BC Museum in Canada, notes that it is challenging to compare extinct to their closest living relatives in the case of dinosaurs. This is because their closest relatives have been evolutionarily distinct for hundreds of millions of years and are highly specialized today. However, the researchers found that theropod teeth functioned similarly to monitor lizards, from the smallest dwarf monitor to the Komodo dragon, allowing for favorable comparisons despite not being closely related.

Mark Witton, another co-author of the study from the University of Portsmouth, mentions that depictions of lips have been a topic of debate among artists for many years. Lipless dinosaurs became more popular in the 1980s and 1990s, and they were later heavily featured in popular culture through films and documentaries, such as Jurassic Park and its sequels and Walking with Dinosaurs.

A half-grown Tyrannosaurus, sporting a full set of lips, runs down Struthiomimus, a beaked ostrich dinosaur. Credit: Mark Witton

The study's findings, published in the journal Science, challenge the popular depiction of carnivorous dinosaurs with perpetually exposed upper teeth hanging over their lower jaws. The change in the depiction of dinosaurs probably reflected a preference for a new, more ferocious-looking aesthetic rather than a shift in scientific thinking.

The research showed that tooth wear in lipless animals differed significantly from that seen in carnivorous dinosaurs. The study also revealed that dinosaur teeth were not disproportionately large relative to skull size, as compared to those of modern lizards, indicating that they could be covered with lips.

In addition, the distribution of small holes supplying nerves and blood to the gums and tissues around the mouth was more lizard-like in dinosaurs than crocodile-like. Moreover, modeling the closure of the lipless theropod jaws demonstrated that the lower jaw had to crush the bones supporting the jaw or disarticulate the jaw joint to seal the mouth, further supporting the hypothesis of lizard-like lips covering their teeth.

A juvenile Edmontosaurus disappears into the enormous, lipped mouth of Tyrannosaurus. Credit: Mark Witton

According to Kirstin Brink, co-author and Assistant Professor of Paleontology at the University of Manitoba, the presence of lips covering teeth is crucial for dental health. Lips prevent teeth from drying out and protect them from damage during feeding or fighting. This is not the case in crocodiles, but the new study suggests that predatory dinosaurs did have lips covering their teeth, similar to those of lizards.

The study also found that dinosaur teeth were not too big to be covered by lips. In fact, even the giant teeth of T. rex were proportionally similar in size to those of living predatory lizards when compared for skull size.

Lead author Thomas Cullen, Assistant Professor of Paleobiology at Auburn University, said that these findings provide important insights into the soft-tissue anatomy and appearance of dinosaurs and other extinct species. Understanding how they fed and maintained dental health can shed light on broader patterns of their and .

T. rex skull and head reconstructions. Credit: Mark Witton

According to Dr. Witton, some people believe that we know very little about how dinosaurs looked beyond some basic features. However, studies like this one are revealing more and more about their appearance. He added that we are now able to determine whether or not certain species had lips or specific types of scales or feathers. The researchers emphasize that their findings do not mean that all extinct animals had covered teeth, as some animals with unique dental features such as saber-toothed mammals, marine reptiles, and flying reptiles with interlocking teeth likely had exposed teeth.

Source: University of Portsmouth

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