Tyrannosaurus had lips, according to a new study

(Mark P. Witton/Science, 2023 https://bit.ly/430FcNu)

Carnivorous theropod dinosaurs, including the famous Tyrannosaurus rex, had lips that covered their teeth when their jaws were closed.

This conclusion was reached by studying the wear patterns of their teeth and comparing the structure of their skulls with modern crocodiles and monitor lizards.

Traditionally, carnivorous dinosaurs are depicted with teeth protruding from their closed mouths, like crocodiles, but in reality their snouts were more like those of monitor lizards.

This idea is supported by the fact that their teeth had thin enamel and served for a long time. If they stuck out with closed jaws, they would wear out much faster.

Now a team of paleontologists at Alabama Polytechnic University doubted that the structure of the mouth of theropods must necessarily be the same as that of crocodiles.

Other modern predatory reptiles have anatomical variants: for example, Komodo dragons (Varanus komodoensis) have analogues of lips.

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LIPS FUNCTION
Crocodiles (along with birds) are among the closest modern relatives of theropods, so it is logical to assume that these two groups share many structural features.

However, studies show that a number of anatomical and physiological features of living crocodiles are associated with their specialization in an aquatic lifestyle.

On the jaws of theropods, such holes were few and lined up, which is more consistent with lizards such as monitor lizards and marine iguanas, rather than modern crocodiles.

The researchers, led by Thomas M. Cullen examined a fully developed tooth from the jaw of a tyrannosaurid Daspletosaurus and found no evidence of enamel wear.

At the same time, in modern crocodiles, the enamel of the teeth wears out heavily from the outside, and sometimes even the dentin is erased.

The authors note that if the tooth enamel is in the mouth, it is wetted by saliva, which makes it better resistant to wear.

In the open air, as on the outside of the teeth of crocodiles, it dries out and wears off faster.

Thus, the wear pattern of the teeth in theropods suggests that they were covered with soft tissues, as in monitor lizards, and were not exposed to the open air, as in crocodiles.

(T. M. Cullen et al/Science, 2023 https://bit.ly/3TYeyAV)

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THE STUDY
It is often claimed that theropod teeth were too large to be covered by lips.

However, using regression analysis, the team demonstrated that the ratio of tooth size to skull size in modern monitor lizards is approximately the same as in theropods.

Even the Salvador monitor lizard (V. salvadorii), which has the largest teeth of any monitor lizard relative to the size of the skull, has lips.

The researchers conclude that tyrannosaurs and other theropods had lips that covered their teeth when their jaws were closed.

The team even said that probably the common ancestor of all dinosaurs, had soft tissues around the mouth arranged in the same way as in scaly reptiles.

This discovery should improve the representation of theropods in paleontological reconstructions and in works of popular culture.

More importantly, it should also be taken into account when studying the feeding habits and ecology of these dinosaurs.

While comparing dinosaurs to modern animals is not always justified, this study provides new insights into the anatomy and physiology of these fascinating creatures.

Sources:

• Science: https://www.science.org/doi/10.1126/science.abo7877
• Smithsonian: https://www.smithsonianmag.com/smart-news/t-rex-had-lips-that-concealed-its-teeth-study-says-180981914/
• ScienceAlert: https://www.sciencealert.com/tyrannosaurus-rex-had-lips-like-a-lizard-scientists-reveal

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