Teenage Tyrannosaurus Had a Taste for Baby Dinosaurs, Rare Fossil Reveals

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Researchers have found a tyrannosaur’s last meal perfectly preserved inside its stomach cavity.

What was on the menu 75 million years ago? The hind legs of two baby dinosaurs, according to new research on the fossil published Friday in the journal scientific advances magazine.

Dinosaur guts and strong evidence of their diets are rarely preserved in the fossil record, and this is the first time the contents of a tyrannosaur’s stomach have been discovered.

The revelation makes this discovery particularly exciting, said co-senior author Darla Zelenitsky, a paleontologist and associate professor at the University of Calgary in Alberta.

“Tyrannosaurs are these large predatory species that roamed Alberta and North America in the late Cretaceous. These were the iconic apexes or top predators that we have all seen in movies, books and museums. They walked on two legs (and) had very short arms,” Zelenitsky said.

“It was a cousin of T. rex, which arrived later, 68 to 66 million years ago. T. rex is the largest tyrannosaur, Gorgosaurus was a little smaller, perhaps at full maturity it would have been 9.10 meters (33 feet).”

Royal Tyrrell Museum of Palaeontology

Darla Zelenitsky, associate professor at the University of Calgary, and François Therrien, curator of dinosaur paleoecology at the Royal Tyrrell Museum of Alberta, next to the young Gorgosaurus specimen.

The tyrannosaur in question, a young Gorgosaurus libratus, would have weighed about 772 pounds (350 kilograms), less than a horse, and would have reached 13 feet (4 meters) in length at the time of its death.

The creature was between 5 and 7 years old and appeared to be picky about what it consumed, Zelenitsky said.

“Its last and penultimate meal was these small bird-like dinosaurs, Citipes, and the tyrannosaur actually only ate the hind limbs of each of these prey. There are really no other skeletal remains of these predators within the stomach cavity. It’s just the back legs.

“He must have killed… both Citipes at different times and then ripped off their hind legs and ate them and left the rest of the carcasses,” he added. “This teenager obviously had an appetite for drumsticks.”

Julius Csotonyi/Royal Tyrrell Museum of Palaeontology

An illustration shows a Gorgosaurus libratus eating dinosaurs belonging to the species called Citipes elegans.

The two baby dinosaurs belonged to the species called Citipes elegans and would have been less than 1 year old when the tyrannosaurus hunted them, the researchers determined.

The almost complete skeleton was found in Alberta’s Dinosaur Provincial Park in 2009.

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It wasn’t immediately obvious that the tyrannosaur’s stomach contents were preserved, but staff at the Royal Tyrrell Museum in Drumheller, Alberta, noticed small bones sticking out when preparing the fossil in the lab and removed a rock from inside its ribcage for further observation. close up.

“Lo and behold, the complete hind legs of two baby dinosaurs, both less than a year old, were present in its stomach,” co-senior author François Therrien, the museum’s curator of dinosaur paleoecology, said in a statement.

Paleontologists were able to determine the ages of both the predator and its prey by analyzing thin slices taken from fossilized bones.

“There are growth marks like the rings of a tree. And we can essentially tell how old a dinosaur is by looking at them, the structure of the bone,” Zelenitsky said.

The fossil is the first solid evidence of a long-suspected dietary pattern among large predatory dinosaurs, said paleoecologist Kat Schroeder, a postdoctoral researcher in Yale University’s department of earth and planetary sciences, who was not involved in the research. .

The adolescent tyrannosaurus did not eat what its parents ate. Paleontologists believe that his diet would have changed throughout his life.

“Large, robust tyrannosaurs like T. rex have bite forces strong enough to hit bones when eating, so we know they bit megaherbivores like Triceratops,” Schroeder said by email. “Young tyrannosaurs cannot bite as deeply and therefore do not leave such feeding trails.”

Royal Tyrrell Museum of Palaeontology

The red square highlights the location of preserved intestinal contents in Gorgosaurus libratus.

He said scientists had previously hypothesized that young tyrannosaurs had different diets than fully grown adults, but the fossil find marks the first time researchers have direct evidence.

“Combined with the relative rarity of juvenile tyrannosaur skeletons, this fossil is very significant,” Schroeder added. “Teeth can only tell us so much about the diet of extinct animals, so finding stomach contents is like picking up the proverbial ‘smoking gun.'”

The contents of the tyrannosaur’s stomach cavity revealed that at this stage of life, the young hunted small, fast prey. It was probably because the predator’s body was not yet prepared for larger prey, Zelenitsky said.

“It’s well known that tyrannosaurs changed a lot during growth, from slender shapes to these robust, bone-crushing dinosaurs, and we know this change was related to feeding behavior.”

When the dinosaur died, its mass was only 10% that of an adult Gorgosaurus, he said.

The voracious appetite of adolescent tyrannosaurs and other carnivores is thought to explain a puzzling feature of dinosaur diversity.

There are relatively few small and medium-sized dinosaurs in the fossil record, particularly in the middle and late Cretaceous period, something paleontologists have determined is due to the hunting activities of young tyrannosaurs.

Royal Tyrrell Museum of Palaeontology

Gorgosaurus libratus was the first young tyrannosaur specimen discovered with its stomach contents preserved within the skeleton.

“In the Alberta Dinosaur Provincial Park, where this specimen comes from, we have a very well sampled formation. And so we have a pretty clear idea of ​​the ecosystem there. More than 50 species of dinosaurs,” Zelenitsky said.

“We are missing medium-sized predators… from that ecosystem. So yes, there has been a hypothesis that, Juvenile tyrannosaurs filled that niche.”

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