Researchers at the University of Alberta have made a “jaw-dropping discovery” that a raptor dinosaur may have dined on a much larger tyrannosaur.

The researchers found bite marks on the jaw of an Albertosaurus, a close relative of Tyrannosaurus rex — and often described by researchers as its “teenage cousin” — that roamed Alberta about 70 million years ago.

The fossil belonged to an eight-year-old Albertosaurus, a sub-adult that had not reached its full size. The bite marks led them to two “wildly divergent explanations” as to what happened to the dinosaur after it died near Drumheller, Alta., about 130 kilometres northeast of Calgary.

Researchers say the most likely scenario is that a raptor — a smaller, two-legged, meat-eating dinosaur — dined on the bigger Albertosaurus after it died of unknown causes.

“This is one of those rare occasions where we actually have information on a carnivore eating a carnivore,” said Philip Currie, a University of Alberta professor of dinosaur paleobiology.

“It’s a pretty big deal,” Currie added, noting that Albertosaurus was one of the dominant predators of its time.

The finding could offer new insight into how carnivorous dinosaurs interacted with one another and the complexity of the prehistoric food web.

Joshua Doyon, a master's student in paleontology at the U of A, led the research into the bite marks.

By measuring the spacing between the marks and comparing it with the teeth of other carnivorous dinosaurs that lived at the same time, researchers determined a raptor was the likeliest explanation.

The alternative hypothesis is that the Albertosaurus was cannibalized by a much younger member of its own species, less than two years old and about two metres long.

Discovery leads to research project The fossil was discovered in 2022 by a member of the public who was canoeing and exploring the badlands north of Drumheller. The find was reported to the Royal Tyrrell Museum, which collected the specimen and prepared it by removing the surrounding rock off of the bone.

As museum staff pieced the fossil back together, they noticed the tooth marks, opening the door to Doyon's research project in 2023.

Doyon said he was interested in studying dinosaur behaviour and the interactions between different species when he approached museum researchers about possible projects.

The specimen offered an opportunity to investigate a feeding interaction that took place tens of millions of years ago.

Currie said the discovery highlights how paleontologists can learn more about dinosaur biology by examining details on fossils, rather than focusing only on identifying and describing the animals.

Details like the tooth marks could help researchers better understand which animals fed on others and how species interacted within prehistoric ecosystems.

Albertosaurus was an apex predator in its ecosystem, while the suspected raptor would have been much smaller — roughly comparable in size to a German shepherd, Currie said.

The finding is significant because it offers rare evidence of one carnivorous dinosaur feeding on another, rather than on prey that ate plants.

The term “raptor” can also bring to mind the dinosaurs depicted in the films, but the animals found in Alberta were smaller than their Hollywood counterparts.

Doyon said the raptors that lived around Drumheller belonged to a group called dromaeosaurs. The local species, Atrociraptor, was about two metres long and considerably smaller than the dinosaurs portrayed in the movies.

Doyon said he hopes paleontologists and members of the public who find dinosaur bones will pay closer attention to small tooth marks that may otherwise go unnoticed.