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Some 75.3 million years in the past, a dinosaur swallowed the Cretaceous equal of a turkey drumstick. It could transform the predator’s ultimate feast.
Inside days of consuming that haunch, the dinosaur — a juvenile Gorgosaurus that stood 5 and a half ft tall on the hip — ended up lifeless in a river. By a stroke of geological luck, sediments quickly lined a lot of the carcass and guarded the dinosaur, and its dinner, from decay.
The ensuing fossil, unveiled Friday within the journal Science Advances, is the primary tyrannosaur skeleton ever discovered with abdomen contents nonetheless preserved inside, yielding an beautiful snapshot of its feeding habits. The fossil additionally preserved a lot of the cranium, pelvis and left facet of the Gorgosaurus’s physique.
Gorgosauruses have been ancestral family members of Tyrannosaurus rex, however this fossil doesn’t comprise a speck of the big herbivores on which grownup tyrannosaurs feasted. As an alternative, this Gorgosaurus ripped the hind limbs off two small feathered dinosaurs. Researchers say the fossil offers the primary direct proof that tyrannosaurs modified what they ate as they aged, which paleontologists had predicted from current fossil proof.
“With this specimen, we’ve bodily proof that younger tyrannosaurs not solely consumed completely different animals than their grownup counterparts, however additionally they attacked or dissected them otherwise,” mentioned François Therrien, the curator of dinosaur paleoecology on the Royal Tyrrell Museum in Drumheller, Alberta, and an writer of the examine.
Beforehand found coprolites — fossilized poop — and bones broken by enamel or abdomen acid present that grownup tyrannosaurs feasted on giant plant-eating dinosaurs resembling Triceratops with bone-crunching gusto. However earlier than they might take down megaherbivores, tyrannosaurs needed to develop bigger, and their skulls and enamel needed to develop huge and sturdy sufficient to generate considered one of nature’s strongest bites.
Juvenile tyrannosaurs, nevertheless, had skinny skulls, slim jaws, blade-like enamel and lengthy legs. Paleontologists had interpreted these traits as indicators that younger tyrannosaurs will need to have been nimble, an thought supported by the brand new fossil. “I jokingly discuss with them because the ballerinas of doom: fast-running, fast-turning and in a position to go after small, fast-running prey,” mentioned Tom Holtz, a paleontologist on the College of Maryland who was not concerned with the examine.
Tyrannosaurs’ means to behave as speedy midsize predators of their youth earlier than maturing into grownup apex predators might have given the group an evolutionary edge by crowding out different predatory dinosaurs. Younger tyrannosaurs’ prowess might even clarify a quirk of North America’s fossil file through the late Cretaceous interval: a “lacking center” predator dimension between heavyweight grownup tyrannosaurs and a menagerie of dinosaurs no bigger than people.
“What is sensible is that these juveniles have been filling that midsized predator area of interest,” mentioned Darla Zelenitsky, a paleontologist on the College of Calgary and an writer of the examine. “They have been the coyotes of the Cretaceous.”
The Gorgosaurus specimen was found in August 2008 by Darren Tanke, a technician on the Royal Tyrrell Museum. Weathering had uncovered its ribs in a hillside in Dinosaur Provincial Park in Alberta. Nonetheless, the fortunate discover got here through the ultimate 45 minutes of the museum’s 2008 subject season, complicating the Gorgosaurus’s restoration. Mr. Tanke didn’t get it into the museum till March 2010.
As Mr. Tanke then eliminated extra rock from the fossil, he determined to dig deeper into the animal’s rib cage. To his shock, he uncovered a number of toe bones too small to belong to the Gorgosaurus, inside a particular space later discovered to signify its abdomen contents.
“This discover would be the discover of my profession,” Mr. Tanke mentioned, whereas reflecting on the greater than 11,000 fossils he has collected for the museum. “I don’t suppose I may ever beat this.”
The abdomen contents encompass hind limbs and a partial tail from beaked dinosaurs generally known as Citipes, which resembled shrunken cassowaries. Every of the 2 Citipes was lower than a yr previous when eaten, and, primarily based on the bones’ diploma of acid put on, the Gorgosaurus ate them through the ultimate week of its life, one a couple of days earlier than the opposite. Regardless of stewing within the Gorgosaurus’s gastric juices, the Citipes bones are so properly preserved that they’re probably the most full fossils of the animal ever discovered.
In all probability, this Gorgosaurus had a number of years left of searching small animals earlier than shifting to greater prey. In 2021, a workforce together with Dr. Therrien and Dr. Zelenitsky discovered that Gorgosaurus couldn’t exert larger chew forces — and tackle giant herbivores — till the age of 11. This dinosaur’s bones point out that it died between the ages of 5 and seven.
Although this Gorgosaurus by no means graduated to the grownup desk, Dr. Therrien thinks there may be little doubt that it fed properly. “All people loves some drumsticks,” he mentioned.
