Some 75.3 million years in the past, a dinosaur swallowed the Cretaceous equal of a turkey drumstick. It will change into the predator’s remaining feast.
Inside days of consuming that haunch, the dinosaur — a juvenile Gorgosaurus that stood 5 and a half toes tall on the hip — ended up useless in a river. By a stroke of geological luck, sediments quickly coated 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 had been ancestral relations 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 supplies the primary direct proof that tyrannosaurs modified what they ate as they aged, which paleontologists had predicted from present fossil proof.
“With this specimen, we have now bodily proof that younger tyrannosaurs not solely ate up totally different animals than their grownup counterparts, however additionally they attacked or dissected them in another way,” mentioned François Therrien, the curator of dinosaur paleoecology on the Royal Tyrrell Museum in Drumheller, Alberta, and an creator of the research.
Beforehand found coprolites — fossilized poop — and bones broken by tooth or abdomen acid present that grownup tyrannosaurs feasted on giant plant-eating dinosaurs similar to Triceratops with bone-crunching gusto. However earlier than they may take down megaherbivores, tyrannosaurs needed to develop bigger, and their skulls and tooth needed to develop large and strong sufficient to generate one among nature’s strongest bites.
Juvenile tyrannosaurs, nevertheless, had skinny skulls, slender jaws, blade-like tooth 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 check with them because the ballerinas of doom: fast-running, fast-turning and capable of go after small, fast-running prey,” mentioned Tom Holtz, a paleontologist on the College of Maryland who was not concerned with the research.
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 report through the late Cretaceous interval: a “lacking center” predator measurement between heavyweight grownup tyrannosaurs and a menagerie of dinosaurs no bigger than people.
“What is sensible is that these juveniles had been filling that midsized predator area of interest,” mentioned Darla Zelenitsky, a paleontologist on the College of Calgary and an creator of the research. “They had 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 remaining 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 characterize 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 include hind limbs and a partial tail from beaked dinosaurs often known as Citipes, which resembled shrunken cassowaries. Every of the 2 Citipes was lower than a 12 months outdated when eaten, and, primarily based on the bones’ diploma of acid put on, the Gorgosaurus ate them through the remaining week of its life, one a number 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 essentially the most full fossils of the animal ever discovered.
In all chance, this Gorgosaurus had a number of years left of looking 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 chunk 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’s little doubt that it fed properly. “All people loves some drumsticks,” he mentioned.
