Dinosaurs don’t need a dentist

The skull bones are among the best preserved bones at the skeleton of Tyrannosaurus rex Tristan Otto. Those bones could be investigated by computed tomography prior to mounting them, making it possible to look at their internal structure without destroying them. With the help of these CT images, scientists from the MfN Berlin now could document, how Tristan Otto grew its teeth. The images demonstrate that the teeth of Tristan Otto were shed and replaced in a regular pattern. Scientists were already aware that the teeth of predatory dinosaurs were replaced in a regular manner. How exactly this process took place, however, has now been described for the first time.

„T. rex Tristan Otto has come to our research museum so that our scientists can learn more about its way of life using state-of-the-art technology. It is a great success for us that our research is now contributing to new insights into the dentition of this twelve-metre-long giant,“ says General Director Johannes Vogel. „At the same time, Tristan Otto is inspiring millions of visitors to nature and science“.

The T.-rex owners Niels Nielsen and Jens Peter Jensen made it possible for scientists at the Museum für Naturkunde Berlin to conduct research on Tristan Otto.

How did T. rex’s teeth grow back?
In contrast to mammals, reptiles, such as crocodiles, regularly shed and replace their teeth. This is possible because the teeth are not used for extensive chewing, and therefore the jaws function despite the absence of single teeth. Tooth replacement is however not by chance, but follows a certain pattern and regularity, so that there are always growing and fully functional teeth together in the jaws. The replacement teeth are visible within the jaws, as they grow slowly into the roots of the functional teeth and resolve them. In the end, the old teeth are shed and replaced by younger ones.

Every second tooth in the tooth change
The computed tomographic images of the tooth bearing bones of Tristan Otto document nicely this pattern of replacement teeth within the jaws. A pattern of retaining only one single replacement tooth before replacing the functional tooth is visible and reconstructed for most alveoli of the jaws. However, in two alveoli (the caverns that accommodate the tooth roots within the jaws), a second, tiny replacement tooth was visible. The youngest replacement teeth have only a thin layer of enamel around the tooth crown, the larger replacement teeth have thicker enamel, fortified at the apex as in the functional teeth. Measurements of the dimensions of the replacement teeth and functional teeth allowed to reconstruct that in the upper jaws of Tristan Otto, the teeth were replaced in a regular alternating pattern between odd and even teeth. So, every second tooth was within the process of being replaced. In contrast to this, in the frontal and most backward part of the lower jaws, teeth were replaced simultaneously.

Successful hunting due to sharp, regrowing teeth
The rate of tooth replacement, and how long single teeth remained in the jaws of Tristan Otto; cannot be reconstructed from the CT images alone – for this, it would be necessary to cut the teeth into pieces. From other specimens of Tyrannosaurus rex however it is known, that the teeth could remain for more than two years in the jaws. As Dr. Schwarz, co-author of the study; says: “The possibility to replace their teeth must have been advantageous for these large predatory theropod dinosaurs, as single lost, broken or worn teeth had no dramatic effect on them – they were simply replaced again and again. It is probable that Tristan Otto had always a set of sharp, functioning teeth in its jaws to assure its successful hunting”.

Published in:
Sattler, Franziska & Schwarz, Daniela 2019. Tooth replacement in a specimen of Tyrannosaurus rex (Dinosauria, Theropoda) from the Hell Creek Formation (Maastrichtian), Montana. Historical Biology (online)
DOI: https://doi.org/10.1080/08912963.2019.1675052

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