You are what you eat, even if you are a dinosaur.
Scientists at the University of Alberta are learning more about the lives of ancient lizards by studying their teeth to see how they were used, and what events.  "If we want to fully understand how these animals lived, we have to understand what they were eating and how they were eating," said Ryan Wilkinson, a university student and co-author of an article published on Thursday at . Current Biology .
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Wilkinson and his colleagues studied scratches left by prey in distress on the teeth of three different raptors and read them as grooves in a record to determine how the dinosaurs broke at lunch. They then used techniques developed to test the strength of the bridges to suggest which prey was preferred.
"The phrase we use in the document is 'click and throw'," Wilkinson said.
Scientists observed three similar dinosaurs – Dromaeosaurus, Saurornitholestes and Troodon.
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Each ate meat, stood on its hind legs, was about two meters long and weighed between 15 and 25 kilograms. They lived almost at the same time in the same environments and are often found together in beds of fossils. The three had streaks like meat knives on the back of the teeth to help cut through the meat.
The team first examined the grooves in the teeth.
Scratches ran in two directions: up and down and angled laterally. That's proof that dinosaurs ate by biting their prey and tearing off the flesh of the corpse, Wilkinson said.
"There is a vertical bite, then an oblique cut when the animal closes its mouth while throwing its head back."
This may be the way all the carnivorous dinosaurs ate. The teeth of Gorgosaurus, a gigantic nine-meter cousin of T. rex, show the same pattern.
But the teeth had more to say than that. The Troodon dentures, called denticles, were much larger than those of the others.
"They have these big, hooked, really weird denticles," Wilkinson said.
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Trying to understand what those denticles would reveal about the Troodon diet, the team built a computer model of the teeth and subjected them to stress tests.
"We use this technique to evaluate the tensions exerted on the teeth during the bite, we apply forces at different bite angles".
When the bite was aligned with the most common scratch angle, the teeth worked well. When the angle moved away from the scratches, the models suggested that Troodon's teeth began to break.
"The prey that fights can exert a lot of uncontrollable force on the teeth at angles that are not really ideal," said Wilkinson.  If it is likely that the prey that struggles back will tear your teeth, you are likely to look for something else. The teeth suggest that Troodon pursued smaller, slower prey, even carrion, and left the harder meals to Dromaeosaurus and Saurornitholestes.
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The study goes a long way in explaining how different dinosaurs fill different niches in their ancient ecosystems. It is one of the first times that these techniques were applied to carnivorous dinosaurs, Wilkinson said.
"There is much more space to analyze this in more detail".