Many of the planet’s most famous killer dinosaurs owe their success to deeply serrated teeth that specialized in tearing through the flesh and crunching on the bones of other dinosaurs. But not only did their teeth have saw-like cutting edges, the tissues within each tooth were arranged in a way that strengthened and improved the function of their fearsome chompers. The findings are published in Scientific Reports this week.

Back in the 1990s, researchers noticed unusual cracks inside the teeth of a predatory dinosaur called Albertosaurus. Like Tyrannosaurus rex and Gorgosaurus (illustrated above), this carnivore belonged to the group of bird ancestors called theropods. At the time, researchers thought that these were caused by the stresses that result from feeding. 

But now, an international team led by Kirstin Brink and Robert Reisz from the University of Toronto Mississauga examined teeth from eight other theropods using a scanning electron microscope and a synchrotron to better understand their structure and chemical composition. The researchers looked at both mature, erupted teeth and immature, unerupted teeth. Since these hadn’t broken through the gums yet, they weren’t exposed to the wear and tear of feeding. 

The team discovered that those internal structures weren’t cracks at all. Rather, they were deep folds within the tooth that strengthened each individual serration, preventing breakage and improving the function. Additionally, these formations -– called deep interdental folds – have extra layers of calcified tissue (or dentine) under the enamel coating to make them extra tough. 

"We proposed a developmental hypothesis that these are structures created when the tooth is first forming," Brink tells Live Science. "It actually helps to deepen the serration within the tooth and strengthen each serration and the tooth overall."

This special tooth structure appears to be unique to theropods. Other extinct animals may have had teeth that resembled these, but they lacked the internal tissue arrangement. The only reptiles living today that have superficially similar teeth are the Komodo dragons of Indonesia. 

"What is so fascinating to me is that all animal teeth are made from the same building blocks, but the way the blocks fit together to form the structure of the tooth greatly affects how that animal processes food," Brink says in a statement. "The hidden complexity of the tooth structure in theropods suggests that they were more efficient at handling prey than previously thought, likely contributing to their success." By efficiently chomping on bones and ripping flesh off large animals and reptiles, theropods prospered for about 165 million years.