Paleontologists have reported that fully grown tyrannosaurs were formidable predators capable of killing large herbivores. However, new research suggests that young tyrannosaurs had a different diet, consisting of much smaller prey. The discovery of a fossil with remains of a last meal provides direct evidence that these carnivores changed their diet as they grew.
The tyrannosaur Gorgosaurus libratus, which lived approximately 77 million years ago in what is now Alberta, Canada, was a dominant predator. Adults used their powerful jaws and teeth to feed on large herbivorous dinosaurs such as Triceratops and duck-billed dinosaurs. The diet of young tyrannosaurs, on the other hand, has been a topic of debate due to their less robust skulls and teeth.
In a new study, researchers describe a fossil of a juvenile Gorgosaurus found in Alberta’s Dinosaur Provincial Park. This specimen was estimated to be about 5 to 7 years old, 4 meters long, and weighed approximately 350 kilograms. The fossilized remains of two smaller dinosaurs, identified as Citipes elegans, were found in its stomach. These smaller prey were likely less than 1 year old and provided fewer calories, suggesting that adult tyrannosaurs would not have bothered with them.
The young Gorgosaurus seems to have been selective in its diet, consuming only the hind legs of the Citipes dinosaurs. The bones indicate that the prey was swallowed within hours or days. Since small raptors like Citipes laid nests with numerous eggs, there were likely many small individuals present.
The discovery of this fossil is considered rare and significant by experts in the field. It supports the idea that young tyrannosaurs fed on smaller prey until they experienced a growth spurt. It is also speculated that adult tyrannosaurs may have provided pieces of larger prey to their offspring based on tooth wear patterns. These findings may help explain why dinosaur diversity was lower compared to other animal groups of the time.
Interestingly, the hind legs of the Citipes specimens found in the Gorgosaurus’s stomach represent the most complete fossils of their species discovered so far. Further research will be conducted to study these specimens more extensively.