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Tyrannosaurs are well known to have been fierce predators at the top of the food chain millions of years ago, but a study by an Alberta researcher shows that reptiles didn’t start their lives that way.
François Therrien, curator of dinosaur paleoecology at the Royal Tyrrell Museum in Drumheller, Alta., Said the study focused on tyrannosaur teeth and their dramatic change as they mature.
He has collaborated with Darla Zelenitsky and Jared Voris of the University of Calgary, as well as with Kohei Tanaka of the University of Tsukuba in Japan.
For the study, published this week in the Canadian Journal of Earth Sciences, researchers looked at the lower jaws of the Albertosaurus and Gorgosaurus, types of tyrannosaurs commonly found in Canada that predated the T. rex millions of years old.
“Our fossil record for these two tyrannosaur species is excellent,” Therrien said of the museum’s collection.
“We have so many specimens of these… which represent a complete growth series from very young individuals who were probably three or four years old to fully developed adults who were over 20 years old.”
By examining a wide array of fossils, the researchers were able to see a significant change in tooth size and jaw strength once the tyrannosaurs reached about 11 years of age.
Feeding behavior did not appear to change over the lifetime of the tyrannosaurs, as their jaws were adapted to capture and grip prey with their mouths, possibly because the forelimbs were too short to grip food, Therrien said.
“Tyrannosaurs were really unique when you look at all the theropods,” he said. “They were atypical… because their bite and skulls were their main weapon in killing their prey. “
But what has changed, he said, is the size of their teeth and their bite force.
A tyrannosaurus at around three years old was still a deadly predator, but it had smaller blade-like teeth that could only slice through flesh. The bite force, Therrien added, was about 10% that of an adult alligator.
This meant that the younger tyrannosaurs ate smaller prey and had to compete with other similarly sized predators such as the Velociraptor.
After the tyrannosaurs turned 11, Therrien explained, they experienced a growth spurt in which their teeth grew larger and larger. By the time the reptiles were adults, their bite force was eight times that of an alligator.
And that meant their diet had changed as well.
“These teeth were better suited to withstand the torsional stresses associated with biting large prey or even crushing bones.”
Therrien said his study shows that young tyrannosaurs were distinct predators that occupied different ecological niches.
“Young tyrannosaurs weren’t just scaled-down versions of mature parents,” he said. “They were creatures that actually had their own way of life.”
This report by The Canadian Press was first published on June 23, 2021.
Daniela Germano, The Canadian Press