Study Reveals Dinosaur Replaced Teeth as Often as Sharks

Allo Cerato cover art by Sae Bom Ra ’19

Talk about high turnover.

A meat-eating dinosaur species that lived in Madagascar some 70 million years ago replaced all its teeth every couple of months or so, a new study has found, surprising even the researchers.

In fact, Majungasaurus grew new teeth roughly two to 13 times faster than those of other carnivorous dinosaurs, says paper lead author Michael D. D’Emic, PhD, assistant professor of biology. Majungasaurus would form a new tooth in each socket every couple of months.

“This meant they were wearing down their teeth quickly, possibly because they were gnawing on bones,” Dr. D’Emic said. “There is independent evidence for this in the form of scratches and gouges that match the spacing and size of their teeth on a variety of bones—bones from animals that would have been their prey.”

Dinosaurs’ teeth worn down from gnawing bones

Some animals that exist today, such as rodents, also gnaw on bones, Dr. D’Emic explained. It’s a way for them to ingest certain nutrients. It also requires exceptionally strong teeth—but Majungasaurus did not have those.

“That’s our working hypothesis for why they had such elevated rates of replacement,” Dr. D’Emic said. The rapid-fire tooth growth puts Majungasaurus in the same league as sharks and big, herbivorous dinosaurs, he added.

This labeled image of surface models shows specimen numbers for CT-scanned isolated Majungasaurus crenatissimus teeth. It appears in the paper “Evolution of High Tooth Replacement Rates in Theropod Dinosaurs” published in the journal PLOS ONE.

Although at least a few hundred meat-eating dinosaur species roamed the Earth, researchers have analyzed tooth-replacement rates for only about a half-dozen of them, Dr. D’Emic said. He also has looked into tooth-replacement patterns in plant-eating dinosaurs.

“I’m hoping this latest project spurs more people to study other species. I bet that will reveal further surprises,” he said. “And hopefully that will lead to a better understanding of how dinosaurs evolved to be successful for so long.”

Importantly, the recent study examined two additional species of predatory dinosaur (Allosaurus and Ceratosaurus), providing an opportunity to consider tooth-growth patterns at a broader scale.

Adelphi professor collaborates with Ohio University researchers, involves Adelphi students

In collaboration with Patrick O’Connor, PhD, professor of anatomy at Ohio University, and PhD student Eric Lund, Dr. D’Emic used a collection of isolated fossil teeth to examine microscopic growth lines in the teeth. These growth lines are similar to tree rings, but instead of being deposited once a year, they were deposited daily. At the same time, the team used computerized tomography (CT) on intact jaws to visualize unerupted teeth growing deep inside the bones. That allowed them to estimate tooth-replacement rates in a large number of individual jaws so they could cross-check their results.

The time-consuming process would not have been possible without the involvement of Adelphi University students: Former undergraduates Elizabeth Mardakhayeva ’18 and Joanna Gavras and current graduate student Thomas Pascucci are co-authors on the paper.

“Future research will be able to use this study to estimate tooth-replacement rate in dinosaurs without destructively sampling teeth,” Pascucci explains.

This work was supported in part by the National Science Foundation, Division of Earth Sciences (EAR_1525915). It appears in the journal PLOS ONE.

See more about Professor D’Emic’s other research on warm-blooded dinosaurs and flowering trees. Initial media coverage of the new study has included stories in The New York Times, Smithsonian Magazine, Fox News, CNN and Newsweek.

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