Majungasaurus, One of the Last Dinosaurs to Walk Earth, Replaced Its Teeth As Fast As Sharks

A meat-eating dinosaur that was one of the last to walk Earth replaced its teeth as often as modern sharks do, scientists have discovered. Majungasaurus, which lived between 66 and 70 million years ago, was found to grow new teeth about once every two months. That is up to 13 times faster than some other carnivorous dinosaurs, such as Tyrannosaurus Rex, which took about two years to grow new teeth.

In a study published in PLOS One, researchers led by Michael D. D'Emic, from Adelphi University in New York, analyzed the tooth replacement patterns in three species of carnivorous dinosaurs—Allosaurus, Ceratosaurus and Majungasaurus. Allosaurus lived between 145 to 155 million years ago, Ceratosaurus lived between 145 and 161 million years ago, while Majungasaurus emerged far later, from 66 to 70 million years ago—the point when dinosaurs went extinct.

Previous research has shown dinosaurs replaced their teeth, with different species doing so at different rates. Before this research, it was thought herbivores replaced their teeth every few weeks or months, while carnivores did so at a slower rate, taking months—if not years—to do so. However, this was based on the study of just 17 species, only three of which were carnivorous. "We show in this new study that some carnivores replaced their teeth on par with rates seen in herbivores, which was surprising," D'Emic told Newsweek.

The team created the largest dental dataset for Majungasaurus, taking scans of their jawbones as well as studying the microscopic growth lines in their teeth. Majungasaurus was an apex predator on its island home of Madagascar. It is one of the few dinosaur species that is known to have been cannibalistic. Because of the amount of preserved skeletal material, it is one of the best-studied species of theropod dinosaur from the Southern Hemisphere.

"The project started as a Majungasaurus-only study," he said. "The reason that species in particular was selected was that thousands of shed fossil teeth are known for it, which is highly unusual for a dinosaur. We wanted to understand why so many shed teeth were present in museum collections. When we got our surprising result—that it replaced its teeth frequently, with a new tooth in each socket on average every 56 days—we wanted some context."

The team analyzed the teeth of the two other species to establish their tooth replacement rate. It was found to be about half as fast as Majungasaurus, but still far faster than the other carnivorous dinosaurs previously studied.

Artist impression of Majungasaurus. The dinosaur lived on Madagascar between about 70 and 66 million years ago. iStock

"I was very surprised—Majungasaurus replaced its teeth as fast or faster than some duck-billed, horned, or long-necked herbivorous dinosaurs," D'Emic said. "This is by far the fastest tooth replacement rate in carnivorous dinosaurs, for example about 14 times faster than the replacement rate in T. rex."

The team says Majungasauruses may have replaced their teeth at this fast rate because they would gnaw on bones, which would wear their teeth down quickly. "[This] is supported by independent evidence in the form of gouges and scratches on many bones from the same geologic layer Majungasaurus is found in, which match the orientation and spacing of Majungasaurus teeth," D'Emic said.

Our understanding of dinosaur tooth replacement is still rudimental. Why, when and how faster tooth replacement rates evolved will require far more research from different species of dinosaur across different times—something the team is now hoping to do.

"With our new study we've increased the sample size for dinosaurs, but still only a fraction of the 1,000 or so known Mesozoic dinosaur species have been studied. There are whole families of dinosaur that this technique hasn't been applied to—I think there are lots of interesting studies using these methods to be done."