Long ago, carnivorous dinosaurs grew little serrations on the back of their teeth called denticles, all the better to eat prey with. As the dinosaurs bit down, their food scraped into the denticles.
From these tiny abrasions — the microwear — and the shape of dino dentition, paleontologists say they can tell not only what these predators ate but how they did so, according to a report published in the journal Current Biology on Thursday. A team of researchers in Spain and Canada have examined the worn denticles in 57 fossil teeth from three different groups of similarly sized dinosaurs, Troodon, Dromaeosaurus and Saurornitholestes, which were about the size of a large swan, as well as a much larger, 9-foot-tall tyrannosaur called a Gorgosaurus.
“We have been able to infer that, even if these different dinosaurs had different types of denticles in their teeth, they were biting in the same way, through a 'puncture and pull' system,” said Angélica Torices, a paleontologist at the University of La Roja in Spain.
The puncture-and-pull maneuver, as its name suggests, is a two-step motion. First a clampdown with the teeth, then a tug backward with the head. This is a very efficient way to obtain food, Torices said.
“As the tooth enters the prey and is drawn backward, the tooth will both puncture and cut through soft tissue,” said Domenic D'Amore, a biologist at Daemen College in New York, who has studied the dentition of carnivorous dinosaurs and was not involved with the research. “The result is meat can be sectioned off a carcass effectively, which is excellent for breaking down large vertebrate prey.”
This eating method has not gone extinct with the dinosaurs. Komodo dragons, the largest living lizards, use it. (Komodo dragons have the sort of dining etiquette that would give Emily Post conniptions: All chomp, very little chew.) Unlike more dainty carnivores, the Komodo dragon requires “minimal input from the jaw muscles when butchering prey,” notes a 2008 study of the lizards' eating habits.
The dinosaurs studied in the new report are a classic picture of the prehistoric meat-eater, with two legs, long tails and skinny forearms. All the types of dinosaurs studied belong to a group of dinosaurs known as theropods. They lived in the Upper Cretaceous period, between 100 million and 66 million years ago. The descendants of the theropod dinosaurs are alive today as birds.
Torices and her colleagues also used a technique from engineering called finite elements analysis, which allowed them to estimate how the tooth structure behaved in various scenarios. The researchers modeled, for instance, the cutting angles and bite forces that the fangs could withstand.
“Most studies using theropod teeth to better understand diet have looked at either tooth anatomy or traces on prey bones,” D'Amore said. “This is novel in that it uses both anatomy and microwear as an indirect measure of behavior. I find it very convincing.”
Though most of the dinosaurs in the study were roughly the same size, Torices said it was likely the animals ate different food despite the same bite method. Troodon teeth were likely to give out if the dinosaur bit at a non-optimal angle, suggesting Troodon avoided prey that put up a struggle. “Possible food sources could have been smaller animals or invertebrates or even carrion,” she said.
Dromaeosaurus and Saurornitholestes teeth, however, could withstand greater stresses. These dinosaurs probably attacked larger prey and were able to sink their mouths into bone, the scientists concluded.
The giant Gorgosaurus had similar tooth structure to the Dromaeosaurus — except its fangs were much larger. Fossil evidence in tyrannosaur dung indicates that these large predators chomped through bones. Their teeth aren't pitted from wear, unlike hyenas and other modern bone-crunchers, but Torices said that can be explained by the fact that dinosaurs continuously replaced their teeth.
“All these dinosaurs were living at the same time and place, so it is important to know if they were competing for food resources or they were aiming for different preys,” Torices said. “Through this work we begin to understand a bit better the interactions between these predatory dinosaurs and the role of troodontids in the ecosystem.”