A dinosaur fossil found in the Alberta badlands has revealed new details about the diet of young meat-eating tyrannosaurs.
The research, published Friday in the journal Science Advances, is based on a well-preserved Gorgosaurus libratus specimen discovered in 2009 by a technician from the Royal Tyrrell Museum in Drumheller, Alta.
鈥淲e describe the first tyrannosaur skeleton found with prey items preserved inside the stomach,鈥� Darla Zelenitsky, an associate professor in the department of earth, energy and environment at the University of Calgary, said in an interview.
鈥淚t鈥檚 a juvenile, or teenage, gorgosaurus 鈥� that had eaten two young and small birdlike dinosaurs called Citipes.鈥�
Gorgosaurus was a tyrannosaur that lived 75 to 77 million years ago, before the Tyrannosaurus rex, in what is now southern Alberta. The specimen was found in Dinosaur Provincial Park, about 220 kilometres east of Calgary.
The four-metre long tyrannosaur had an estimated weight of 335 kilograms and, based on the research, would have been about five to seven years old when it died.
Zelenitsky said the fossil represents the first solid evidence of the diet of juvenile tyrannosaurs.
鈥淚t鈥檚 really an exciting find, because it鈥檚 unique and very unusual to find something like this, especially so well preserved.鈥�
Co-author Fran莽ois Therrien, curator of dinosaur palaeoecology at the Royal Tyrrell Museum, said it鈥檚 an important discovery for several reasons.
鈥淪keletons of young tyrannosaurs are extremely rare,鈥� he said. 鈥淭heir bones are smaller and more fragile, so either they didn鈥檛 get fossilized back in (the) Cretaceous or they just get destroyed before we actually find them in the badlands.鈥�
He said a technician noticed some toe bones while the specimen was being cleaned.
鈥淭he toe bones were definitely too small to belong to the tyrannosaur and they were coming through the rib cage from inside the animal,鈥� Therrien said.
They decided to prepare the specimen from the inside out and discovered that the bones of the two small dinosaurs were preserved in the stomach area.
鈥淭hat was truly amazing, because the last meal 鈥� or in-place stomach contents 鈥� of a tyrannosaur had never been discovered before, so that was really exciting,鈥� Therrien said.
The research, he added, took many years because there were so many pieces to put together. That included identifying the bones in the stomach, determining the age of those bones and the tyrannosaur, and figuring out how long the bones had been in the stomach.
Therrien said it shows a change in diet for tyrannosaurs as they matured.
鈥淔or a long time, we鈥檝e known that adult and juvenile, or young, tyrannosaurs were very, very different physically.鈥�
Adult tyrannosaurs, he said, were large animals with massive skulls and robust teeth that fed on plant-eating duckbill and horned dinosaurs, while juveniles were lightly built and athletic with blade-like teeth and long legs.
鈥淲e suspected that they were hunting something else, but we did not know what. Now this specimen finally shows young tyrannosaurs hunted small and young dinosaurs.鈥�
Therrien said a transition from juvenile to adult, similar to people going through puberty, likely took place for the tyrannosaur around the age of 11.
Researchers determined that the young dinosaur was quite surgical in how it ate its prey.
鈥淚t went around and dissected away the back legs, swallowed those whole and basically didn鈥檛 eat anything else of the carcass,鈥� said Therrien. 鈥淚t took the hind legs and nothing else, probably because that was the meatiest part of the animals.鈥�
Zelenitsky added the young gorgosaurus appeared to be quite a fussy eater.
鈥淚magine that as a teenager,鈥� she said with a laugh. 鈥淭his gorgosaurus had an appetite for Citipes drumsticks, I guess.鈥�
The research showed it had eaten the two birdlike dinosaurs in separate feeding events.
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