You are what you eat

Photo: The Canadian Press

A biting Saurornitholestes dinosaur is shown in a handout illustration.

You are what you eat, even if you're a dinosaur.

University of Alberta scientists are learning more about the lives of the ancient lizards by studying their teeth to see how they used them — and what on.

"If we're to fully understand how these animals were living, we need to understand what they were eating and how they were eating," said Ryan Wilkinson, an undergraduate and co-author of a paper published Thursday in Current Biology.

Wilkinson and his colleagues studied scratches left by struggling prey on the teeth of three different raptors and read them like grooves on a record to determine how the dinosaurs tore into lunch. They then used techniques developed to test the strength of bridges to suggest what prey was preferred.

"The phrase we use in the paper is 'puncture and pull,'" Wilkinson said.

The scientists looked at three similar dinosaurs — Dromaeosaurus, Saurornitholestes and Troodon.

Each were meat-eating, stood on their hind legs, were about two metres long and weighed between 15 and 25 kilograms. They lived at about the same time in the same environments and are often found together in fossil beds. All three had serrations like steak knives on the back of their teeth to help slice through flesh.

The team first examined grooves on the teeth.

The scratches ran in two directions: up and down and angled laterally. That's evidence that dinosaurs ate by chomping down into their prey then tearing the flesh off the carcass, said Wilkinson.

"There's a vertical plunging bite, then an oblique cut as the animal closes its mouth as it draws its head backwards."

This may be the way all meat-eating dinosaurs ate. Teeth from Gorgosaurus, a gigantic, nine-metre cousin of T. rex, show the same pattern.

But the teeth had more to say than that. Troodon's serrations, called denticles, were much larger than those of the others.

"They have these large, hooked denticles, really bizarre," Wilkinson said.

Trying to understand what those denticles might reveal about Troodon's diet, the team built a computer model of the teeth and subjected them to stress tests.