Most of us hope that we’ll only have to lose one set of teeth during our lifetime, but for most animals, replacing their teeth is just another fact of life. These so-called polyphyodont animals have to replace their teeth throughout life because their diets wear down their teeth, with herbivores chomping away on tough plant material, generally replacing their teeth more frequently than carnivores dining on softer, tooth-friendlier meat. Like many modern animals, it turns out that dinosaurs were also accustomed to replacing their teeth and in their recent PLOS ONE paper, Michael D’Emic and his team investigate teeth replacement rates in three theropod dinosaurs.
The starting point for this study began during D’Emic’s postdoc at Stony Brook University where he came across drawers and drawers full of shed Majungasaurus teeth. Intrigued, Michael D’Emic now an Associate Professor at Adelphi University, decided to start investigating tooth formation and replacement rates in this late Cretaceous carnivorous dinosaur. Collaborating with Patrick O’Connor at Ohio University, D’Emic decided to look at the teeth replacement rates in two other carnivorous theropod dinosaurs, Allosaurus and Ceratosaurus.
D’Emic and O’Connor were also joined on the project by two graduate students and two undergraduate students. The team began the study with the painstaking task of CT scanning 52 Majungasaurus teeth and 15 Majungasaurus tooth-bearing elements, as well as 11 Allosaurus and 1 Ceratosaurus tooth-bearing elements. Whilst many of the specimens came from collections D’Emic had access to during his postdoc at Stony Brook, many other museums contributed specimens to the study with a little help from the medical field as D’Emic explains: “I had to visit some museums out west for other projects, and while there, I was able to arrange some CT scans at local hospitals. Without the help of those radiology departments, and the curators who helped set up the contacts, we couldn’t have completed our study.” Equipped with the CT scans, the team were then able to undertake various measurements such as tooth length for all three dinosaurs. In addition, the team measured the volume of a sample of the teeth and took thin sections of 19 Majungasaurus teeth as well as 1 Allosaurus and 1 Ceratosaurus tooth.
Using the thin sections, the team could observe fine incremental lines of Von Ebner, which, like tree-rings, could tell the team how long it would take for the teeth to form as each of these lines represents the cyclical activity of cells that produce the bulk of the tooth’s tissue, known as dentine. Based on the thickness they measured, D’Emic and his colleagues estimate that for the largest tooth the formation times would be 293, 359 and 337 days for the Majungasaurus, Allosaurus and Ceratosaurus respectively. Using this knowledge and the other measurements taken from the CT scans, the authors were then able to generate a age-tooth length model to estimate teeth replacement rates non-destructively. From the model, they estimated that Majungasaurus, Allosaurus and Ceratosaurus replaced their teeth every 56, 104, and 107 days respectively.
The rapid replacement rate for Majungasaurus was a bit of a surprise, as graduate student Thomas Pascucci notes: “High rates of replacement are more associated with herbivorous dinosaurs that process lots of tough plant material and constantly need to replenish worn teeth. Majungasaurus teeth were replaced at a similar speed, once every couple of months.” Going on to speculate as to the reason for a high rate of replacement, Pascucci recalls: “There has been previous evidence that Majungasaurus possibly ate bones based on tooth marks found on lots of fossils. Our study really helps to corroborate that idea because eating bone would cause teeth to wear and be replaced very quickly.’
Through the patient work of D’Emic and his team, they have now amassed a large dataset of CT scans and provided a way to model tooth replacement rates from CT scans without the need for destructive thin sectioning. In doing so, other researchers will hopefully be able to add to our understanding of tooth replacement rates in dinosaurs and provide an insight into the diets and lifestyles of these extinct animals.
D’Emic MD, O’Connor PM, Pascucci TR, Gavras JN, Mardakhayava E, Lund EK (2019) Evolution of high tooth replacement rates in theropod dinosaurs. PLoS ONE 14(11): e0224734.
Or read Micheal D’Emic work on teeth replacement rates in herbivorous Sauropod Dinosaurs:
D’Emic MD, Whitlock JA, Smith KM, Fisher DC, Wilson JA (2013) Evolution of High Tooth Replacement Rates in Sauropod Dinosaurs. PLoS ONE 8(7): e69235.
The featured Paleo Art is by Sae Bom Ra a student at Adelphi University.