Last meal: for the first time, scientists have revealed the stomach contents of a “picky” tyrannosaurus

What was on the menu of the creatures that lived on Earth 75 million years ago? The hind legs of two baby dinosaurs, according to a new fossil study published Friday in the journal Science Advances.

Dinosaur guts and hard evidence of their diet are rarely preserved in the fossil record, and this is the first time the stomach contents of a T. rex have been discovered, CNN reports.

What makes this discovery particularly exciting is co-author Darla Zelenicki, a paleontologist and assistant professor at the University of Calgary in Alberta.

“Tyrannosaurs are large carnivorous species that roamed Alberta and North America during the Late Cretaceous period. These were the iconic apex predators that we have all seen in films, books and museums. They walked on two legs and had very short arms,” Zelenicki says. – It was a cousin of the Tyrannosaurus rex, which appeared later in time, 68-66 million years ago. Tyrannosaurus is the largest of the tyrannosaurs, Gorgosaurus was slightly smaller, perhaps 9-10 meters in adulthood.”

The tyrannosaurus in question, a young Gorgosaurus libratus, weighed about 350 kilograms – less than a horse – and reached 4 meters in length at the time of death.

According to Zelenicki, the creature was between 5 and 7 years old, and was apparently picky about what it ate: “Its last and penultimate meal was these little bird-like dinosaurs, Citipes, and the Tyrannosaurus rex only ate its hind limbs.” each of these mining targets. There are no other skeletal remains of these predators in the stomach cavity. These are just the back legs. “He must have killed… both of these dinosaurs at different times, and then tore off the back legs and eaten them, leaving the rest of the carcasses,” she added. “Clearly this teenager had an appetite for drumsticks.”

The researchers determined that both baby dinosaurs belonged to the species Citipes elegans and were less than 1 year old when the Tyrannosaurus rex hunted them down and gobbled them up.

An almost complete skeleton was found in Alberta Dinosaur Provincial Park in 2009, CNN notes.

That the T. rex’s stomach contents were preserved was not immediately obvious, but staff at the Royal Tyrrell Museum in Drumheller, Alberta, noticed small protruding bones while preparing the fossil in the laboratory and removed it from the chest to take a closer look.

“Lo and behold, in its stomach were the entire hind legs of two baby dinosaurs, both less than a year old,” one of the lead authors, Francois Therrien, the museum’s curator of dinosaur paleoecology, said in a statement.

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

“There are traces of growth, similar to the rings of a tree. And we can essentially tell how old a dinosaur is by looking at them, at the bone structure,” explains Zelenicki.

The fossil provides the first definitive evidence for the long-hypothesized diet of large carnivorous dinosaurs, said paleoecologist Kat Schroeder, a graduate student in Yale University’s Department of Earth and Planetary Sciences who was not involved in the study.

The teenage Tyrannosaurus rex ate differently than its parents. Paleontologists believe that its diet changed throughout its life.

“Large, robust tyrannosaurs like Tyrannosaurus Rex have enough bite force to hit bone when they eat, which is why we know they bit megaherbivores like Triceratops,” Schroeder points out. “Young tyrannosaurs cannot bite as deeply and therefore do not leave such feeding marks.”

She said scientists had previously hypothesized that the diet of juvenile tyrannosaurs was different from that of fully developed adults, but the fossil find marks the first time researchers have had direct evidence.

“Combined with the relative rarity of juvenile tyrannosaur skeletons, this fossil is very important,” adds Schroeder. “Teeth can tell us a lot about the diet of extinct animals, so finding stomach contents is like finding the proverbial smoking gun.”

The contents of the Tyrannosaurus’s stomach cavity showed that at this stage of life, the juveniles hunted fast, small prey. This was likely because the predator’s body was not yet adapted for larger prey, says Darla Zelenicki: “It’s well known that tyrannosaurs changed a lot as they grew, from slender forms to these tough, bone-crushing dinosaurs, and we know that this change was associated with eating behavior.”

According to her, when the dinosaur died, its mass was only 10% of the mass of an adult Gorgosaurus. The voracious appetites of juvenile tyrannosaurs and other carnivores were thought to explain the puzzling feature of dinosaur diversity.

There are relatively few small and medium-sized dinosaurs in the fossil record, especially those dating back to the mid-to-late Cretaceous period – something paleontologists have determined is due to the hunting activities of young tyrannosaurs.

“In Alberta Dinosaur Provincial Park, where this sample is from, we have a very well sampled formation. And so we have a pretty good idea of ​​the ecosystem there. “More than 50 species of dinosaurs,” Zelenicki says. “We don’t have enough medium-sized predators in this ecosystem.” So, yes, it was hypothesized that young tyrannosaurs filled this niche.”