Gorgosaurus libratus feeding on Citipes elegans. (Artistic illustration)
Agence France-Presse
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For the first time, paleontologists have discovered prey in the stomach of a Tyrannosaurus skeleton, revealing that in their youth these powerful dinosaurs only had an appetite for small ones. “drumsticks”, according to a study published in the journal Science Advances (New window) (in English).
The stomach contents of Gorgosaurus, a member of the tyrannosaur family that includes the famous T. rex, allows us to understand how the animal went from a rather small juvenile stage to that of a gigantic, bone-crushing adult and super predator.
The Gorgosaurus – meaning fearsome lizard – was between five and seven years old when it died, around 75 million years ago x27;years. Its fossilized skeleton was discovered in 2009 in Dinosaur Provincial Park, in Alberta, which is full of dinosaur remains.
While studying the specimen, paleontologists notice something strange in its stomach. They are amazed to discover the remains of the last meal of this young tyrannosaurus still preserved, François Therrien, from the Royal Tyrrell Museum of Paleontology, lead author of the study, tells AFP.
Even more surprising: the small leg bones that protruded from its ribcage belonged to young bird-like dinosaurs, the Citipes.
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Scientists believe that the Citipes had feathers, wings and a beak , and that they walked on two legs, a bit like current cassowaries, specifies François Therrien.
Prey similar to turkeys, well smaller than the immense herbivorous dinosaurs that adult tyrannosaurs loved.
The young carnivore, a picky eater, would have used its sharp teeth to carve only the drumsticks of the two baby Citipes, suggests Darla Zelenitsky, researcher at the University of Calgary.
This adolescent Gorgosaurus appeared to have appetite for drumsticks.
A quote from Darla Zelenitsky, University of Calgary
This discovery provides a rare clue to how tyrannosaurs, which measured one meter long at birth, grew to become these immense predators, among the largest in all time.
This fossil is the first robust evidence that tyrannosaurs radically changed their diet as they reached adulthood, continues the paleontologist.
As juveniles, these dinosaurs had thin heads and legs, sharp knife-like teeth for dissecting carcasses, and must have been able to run fast enough to catch their prey.
An appearance probably closer to small velociraptors than to the giant T. rex, two star species from the film Jurassic Park.
But around the age of 11, reaching middle age, they saw their size increase almost tenfold and weighed more than 3 tons. Their heads and jaws widened, their teeth thickened, becoming capable of crunching enormous bones.
This spectacular transformation would be due to this change in diet, the tyrannosaurs abandoning the drumsticks enjoyed in their youth to attack the giant plant-eating dinosaurs.
A radical change in diet is not so rare in the animal kingdom: crocodiles and Komodo monitor lizards thus switch from insects to rodents, and end up eating large mammals, explains François Therrien.
The Gorgosaurus fossil supports the theory that young tyrannosaurs, including the T. rex, played a role as mesopredators – secondary predators – before becoming superpredators (or apex predators) at the top of the food chain.
This change is probably the reason why tyrannosaurs were so successful and dominated their ecosystems at the end of the Cretaceous in North America and Asia, concludes the paleontologist.