Paleontologists in Canada have found a 75-million-year-old skeleton of a juvenile of the tyrannosaurid dinosaur Gorgosaurus libratus with the remains of two young individuals of the small dinosaur Citipes elegans in its abdominal cavity.
Tyrannosaurids are a group of carnivorous dinosaurs that dominated the ecosystems of Asia and North America near the end of the Cretaceous period, between 80 and 66 million years ago.
Among the largest land predators to have ever existed, they grew from meter-long hatchlings to multiton sizes (9- to 12-m long, 2,000 to 6,000 kg) over the course of their life span.
Juveniles were gracile with narrow skulls, blade-like teeth, and long slender hind limbs, whereas adults were robust with massive skulls and large incrassate teeth and were capable of generating bone-crushing bites.
These changes suggest that tyrannosaurids underwent a major dietary shift, in which juvenile and adult individuals occupied different ecological niches.
Fossil evidence reveals that dinosaurian megaherbivores (i.e., species with an adult mass of over 1,000 kg, including ceratopsids, giant ornithomimosaurs, hadrosaurids, and sauropods) were common prey items of large tyrannosaurids, a diet for which the necessary adaptations and bite forces only developed when individuals reached late juvenile or early subadult growth stages.
“Unfortunately, fossil evidence for diet in young tyrannosaurids is largely unknown, thus limiting our understanding of ontogenetic dietary shifts in these iconic predators,” said lead author Dr. François Therrien, a paleontologist at the Royal Tyrrell Museum, and colleagues.
In their research, the authors examined a well-preserved specimen of Gorgosaurus libratus found in Dinosaur Provincial Park in Alberta, Canada.
“Gorgosaurus libratus was a tyrannosaur that lived 75 million years ago — several million years before Tyrannosaurus rex — in what is now southern Alberta,” they said.
“The age of this individual when it…
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