Fossil Friday: this meat-eating dino could grow a fresh tooth in 60 days

One meat-eating dinosaur from today’s Madagascar replaced all its teeth once every few months, according to a new study.

CT scan-generated models of the jaws of Majungasaurus (left), Ceratosaurus (center), and Allosaurus (right), with microscopic views of the interior of their teeth below.
Image credits Michael D’Emic et al., 2019, PLOS One.

Majungasaurus, a species of dinosaur that went extinct around 70 million years ago, could replace a tooth in around 56 days, reports a new paper. This rate of growth is similar to that of herbivorous dinosaurs — whose teeth see a lot of heavy use — but very quick for a meat-eater.

A gnashing of teeth

“This meant [Majungasaurs] were wearing down on their teeth quickly, possibly because they were gnawing on bones,” says paper lead-author Michael D. D’Emic, an assistant professor of biology at Adelphi University.

“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.”

D’Emic worked with Patrick O’Connor, professor of anatomy at Ohio University, to examine a collection of isolated fossil teeth for microscopic structures known as growth lines. These are fairly similar to tree rings but form on a daily basis rather than once a year.

At the same time, they used computerized tomography (CT) on fossil Majungasaurus jaws to see how unerupted teeth grew inside of the bone. Taken together, the two sets of data allowed the team to estimate the rate of tooth replacement. Several jaws were used for this step and the results cross-checked between them to avoid errors.

The team further looked at two related theropods, Allosaurus and Ceratosaurus, and performed the same analysis.

Majungasaurus definitely took the cake, with a tooth growth rate of roughly 56, 104, and 107 days per tooth, respectively. Judging from other animals that have elevated rates of tooth replacement today, such as rodents, the team believes this is evidence of Majungasaurus gnawing on bones. Such behavior is meant to secure access to certain nutrients that may otherwise be scarce or hard to acquire, the team notes, but also requires exceptionally strong teeth — which Majungasaurus didn’t have. Its softer teeth would get worn out very fast if used in such a way, they write, which would explain why it needed to regrow them so often, and so fast.

“That’s our working hypothesis for why they had such elevated rates of replacement,” D’Emic said.

For comparison, the team explains that Tyrannosaurus rex likely evolved “exceedingly robust teeth and slow replacement rates”

The paper “Evolution of high tooth replacement rates in theropod dinosaurs” has been published in the journal PLOS ONE.

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