Young tyrannosaur found with baby dinosaurs in its stomach

Scientists have made a rare and extraordinary fossil find in Alberta — a young tyrannosaur with the remains of two baby dinosaurs inside its stomach.

The discovery offers new hints about how tyrannosaurs’ behaviour and their role in ecosystems changed as they grew, say the Canadian researchers who led their study, published Friday in Science Advances.

Fewer than two dozen dinosaurs have ever been found with stomach contents, and most of them have been plant eaters, making this a very rare find.

And in fact, the meals themselves — the legs of two juvenile bird-like dinosaurs called Citipes elegans — were also an exceptional find, said Francois Therrien, a Canadian paleontologist who co-led the study.

“They’re very rare animals,” he said. “What’s really interesting is…the stomach contents are the most complete skeletons of citipes ever discovered.”

About 75 million years ago, during the Late Cretaceous, the badlands of Alberta were a subtropical coastal plain on the western shore of an inland sea that divided North America. Herds of duck-billed dinosaurs like parasaurolophus, horned dinosaurs like centrosaurus and dome-headed dinosaurs like stegoceras were among the many species that grazed among palm trees and evergreens along winding rivers, where they were hunted by the huge tyrannosaur Gorgosaurus libratus.

Many remains of these giants have been preserved and excavated, but the more fragile bones of smaller and younger dinosaurs are much rarer.

So there was a lot of excitement when Darren Tanke, a technician from the Royal Tyrrell Museum in Drumheller, Alta., spotted the bones of a young tyrannosaur sticking out of the ground in Dinosaur Provincial Park in 2009. At the time of its death, it was just four metres long — less than half the length of a school-bus sized adult — and just a third of a tonne or a tenth of its adult weight. The researchers later estimated it was between five and seven years old — still years away from transitioning to an adult, which started at around eleven years old.

Dinosaurs inside a dinosaur

After excavation, Tanke brought it back to the…