Bite marks on baby tyrannosaur suggest cannibalism or scavenging

Bite marks on the fossilized jaw of an adolescent Albertosaurus appear to represent the first known evidence of a smaller dinosaur scavenging a much larger tyrannosaur, according to a study published in the Journal of Paleontology. But the researchers also haven't ruled out a darker possibility: cannibalism by a baby.

Albertosaurus, a close relative of Tyrannosaurus rex, lived in what is now Canada during the Late Cretaceous period, about 73 to 67 million years ago. A full-grown adult reached over 30 feet in length and weighed around 6,000 pounds, making it the region's apex predator. The specimen in the study was only 8 to 10 years old at death, what paleontologists call a teenager, but it was already 19 feet long and weighed about 1,170 pounds.

The bite marks on the lower jaw show no signs of bone healing, which means the animal was bitten around the time of death. That strongly suggests the biter was a scavenger, or at least a carnivore that came upon an already dead or dying prey. And it was much smaller than the Albertosaurus.

"This turns everything on its head, because you're dealing with a very small dinosaur eating a very big, mean, nasty dinosaur like a tyrannosaur," study co-author and University of Alberta paleontologist Philip Currie said in a video explainer.

The most likely suspect, the researchers say, is a pack of dromaeosauridae, or raptors, the family that includes Velociraptor and Utahraptor. One species that lived alongside Albertosaurus is Albertavenator curriei, a feathered, sickle-clawed hunter. The bite marks match its tooth spacing.

But the spacing also matches the jaw of an even younger Albertosaurus, about 6.5 feet long. If that's who bit the dead teenager, the authors say, it would be a case of cannibalism by a baby.

"If it is a young Albertosaurus, this would be an event of cannibalism — by a baby," said study co-author and University of Alberta paleontologist Joshua Doyon.

Cannibalism is common in the fossil record, the researchers note, but direct evidence is extremely rare. However the case is resolved, the fossilized leftovers reveal a complex prehistoric food chain where the top predator could end up as someone else's meal.

• Albertosaurus
• cannibalism
• Joshua Doyon
• Journal of Paleontology
• Philip Currie
• raptors