In a groundbreaking discovery, scientists revealed that prey has been found inside the stomach of a tyrannosaur skeleton for the first time, uncovering the early dietary preferences of these mighty dinosaurs. The Gorgosaurus, a member of the tyrannosaurid family akin to the T-Rex, provided insights into the growth trajectory of these dinosaurs, transitioning from slender juveniles into colossal, apex-predator adults.
The Gorgosaurus, ominously named the “dreadful lizard,” met its demise over 75 million years ago at the age of approximately six, as detailed in a recent study published in Science Advances. Discovered in 2009 at Dinosaur Provincial Park, east of Calgary, Canada, the skeleton yielded a surprising twist when examined in the lab.
Lead author Francois Therrien of the Royal Tyrrell Museum expressed amazement at finding “the remains of the last meal of this young tyrannosaur still preserved in place.” What added to the astonishment was the revelation that the small leg bones protruding from the tyrannosaur's ribcage belonged to two young bird-like dinosaurs known as Citipes.
Citipes, thought to possess feathers, wings, a beak, and a two-legged gait resembling modern-day cassowaries, presented a unique dietary choice for the young Gorgosaurus. These smaller creatures stood in contrast to the larger herbivores typically associated with adult tyrannosaurs' diets. Study co-author Darla Zelenitsky, a paleontologist at the University of Calgary, characterized the teenage Gorgosaurus as a “fussy eater,” utilizing its sharp teeth to selectively carve out the legs of the two baby Citipes. In her words, “This teenage Gorgosaurus seems to have had an appetite for drumsticks.”
Not always an apex predator
The newfound revelation provides a rare glimpse into the developmental stages of tyrannosaurs, shedding light on their transformation from one-meter-long juveniles to Earth's formidable predators. According to Zelenitsky, this fossil stands as the inaugural concrete evidence showcasing how tyrannosaurids underwent a significant shift in their diet during the transition from adolescence to adulthood.
In their youth, young tyrannosaurs boasted slender heads, legs, and knife-like teeth suited for dissecting carcasses. Their agility likely allowed them to chase down prey akin to turkey-sized animals, resembling the velociraptors depicted in “Jurassic Park” more than the iconic giant T-Rex, Zelenitsky noted. However, by the time these creatures reached around 11 years of age, a remarkable change occurred. Their bodies ballooned nearly tenfold, surpassing 3,000 kilograms (6,600 pounds) in weight.
During this growth spurt, their heads broadened, and their teeth transformed into formidable tools likened to “killer bananas,” capable of crunching through substantial bones. This metamorphosis was driven by a dietary shift, with the dinosaurs abandoning the drumsticks of their youth to prey upon massive plant-eating dinosaurs.
Such dramatic dietary changes, though striking, find parallels in the animal kingdom—examples include crocodiles and Komodo dragons transitioning from insects to rodents and eventually large mammals, as highlighted by Therrien.
The Gorgosaurus fossil supports the theory that young tyrannosaurs, including the T-Rex, played the role of “mesopredators” in the food chain before evolving into apex predators. This transition, according to Therrien, likely played a pivotal role in the success and dominance of tyrannosaurs in North America and Asia during the Cretaceous period.