Tyrannosaur’s Abdomen Contents Have Been Discovered for the First Time

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By Calvin S. Nelson

For the primary time, scientists have unearthed direct proof of what a tyrannosaur—usually considered the epitome of fearsome predators—really ate.

The fossilized abdomen contents of 1 member of this dinosaur household have been described in a brand new examine printed on Friday in Science Advances. This exceptional discovery offers insights into the tyrannosaur eating regimen and the animal’s place in historic ecosystems, each of which have beforehand solely been hypothesized about.

Darren Tanke, a fossil preparator on the Royal Tyrrell Museum of Paleontology in Alberta, discovered the specimen within the province’s Dinosaur Provincial Park and delicately eliminated it from the rock through which it was encased. He known as it “the invention of his life,” in keeping with examine co-author François Therrien, the museum’s curator of dinosaur palaeoecology.

The examine examines remnants of two small oviraptorosaur—feathered dinosaurs with a toothless beak—that have been discovered within the abdomen of a younger Gorgosaurus libratus, a sort of tyrannosaurid. (The household contains this species’ extra well-known cousin Tyrannosaurus rex.) Earlier than the brand new fossil discover, scientists might solely infer something concerning the tyrannosaur eating regimen. Such inferences have been primarily based on issues like fossils’ cranium and tooth construction, chew marks on megaherbivores’ fossils and no less than one coprolite, or fossilized feces. Bones discovered close to one tyrannosaur fossil have additionally been interpreted as abdomen contents. The circumstances that may result in the fossil preservation of abdomen contents are uncommon: an animal would wish to die earlier than the entire digestion of prey after which be quickly buried by mud or one other medium.

“Direct proof of eating regimen in dinosaurs is frustratingly uncommon,” says Lindsay Zanno, head of paleontology on the North Carolina Museum of Pure Sciences and an affiliate analysis professor at North Carolina State College, who was not concerned within the new analysis.

Gorgosaurus skeleton left view exhibiting location of abdomen contents. Credit score: Copyrights Royal Tyrrell Museum of Palaeontology

Gorgosaurus lived within the late Cretaceous interval, roughly 80 million to 66 million years in the past. Leggy and slender with bladelike tooth in its youth, it developed into an enormous apex predator as an grownup, virtually twice the peak of a giraffe and weighing as a lot as an elephant. That transformation made paleontologists suppose the animal underwent a major dietary shift throughout its lifetime. A younger Gorgosaurus wouldn’t be anticipated to assault the megaherbivores it might deal with as an grownup; smaller prey would make extra sense.

Bone development evaluation revealed that this tyrannosaur was a juvenile between 5 to seven years outdated and that each of its prey had lived for lower than a yr. The differing quantity of abdomen acid etching on the prey remnants signifies the animals might have been consumed inside hours or days as separate meals. And the truth that the remnants included absolutely articulated legs from two oviraptorosaurs of the identical age, dimension and species suggests the animals have been a well-liked menu merchandise of this specific tyrannosaur.

The oviraptorosaur legs enabled the staff to determine the prey as Citipes elegans—specimens that have been “extraordinarily uncommon” by way of their comparatively pristine situation. “Mockingly, the tyrannosaur abdomen really protected the Citipes, enabling it to be preserved—which is kind of neat,” says examine co-author Darla Zelenitsky, an affiliate professor on the College of Calgary. These Citipes fossils are, she provides, “essentially the most full stays identified for that species.”

Gorgosaurus in all probability “dismembered the small prey, swallowed the legs and left the remainder of the physique on the market,” Therrien says. He suggests these legs might have been “the meatiest half” of the animal and wonders, with amusing, if maybe this Gorgosaurus “didn’t need to be bothered having to cough up some feathers.”

“With the invention of this exceptional specimen, now we have direct, irrefutable proof of not solely what this species was snacking on,” Zanno says, “however the gory particulars of the way it went about it.”

Oviraptorosaur nests sometimes contained no less than 30 or extra eggs. With such giant broods, “you can think about, at sure instances of yr, relying upon the species and when their breeding season is, this is able to not be an unusual prey for predators,” Zelenitsky says. That’s why she isn’t stunned to seek out stays of this species on this Gorgosaurus’ abdomen, particularly as a result of she “can’t see the adults going after these tiny little chicken-sized or turkey-sized dinosaurs.”

Zelenitsky speculates that, like birds and crocodiles—intently associated animals that share a standard ancestor with dinosaurs—Gorgosaurus might have had a two-part abdomen. The positioning of the 2 Citipes, she notes, strongly suggests this chance, with the legs of the primary meal exhibiting extra “chemical digestion,” and the legs of the final meal exhibiting extra “mechanical digestion or breakdown.”

This discovery additionally helps assist what some paleontologists consider is the important thing to tyrannosaur evolutionary success: their potential to occupy totally different ecological niches all through their lifetime. One paleontological thriller facilities round a putting shift in Cretaceous ecosystems. The place as soon as there have been a wide range of carnivore sizes and species, by the top of the Cretaceous in Asia and North America, there have been solely two sorts: large tyrannosaurs and far smaller dromaeosaurs (feathered theropods reminiscent of these of the genus Velociraptor)—and “nothing in between,” Therrien says.

It has been hypothesized that tyrannosaurs have been in a position to occupy the entire ecological niches as soon as held by former midsize and enormous carnivores over the course of their growth: the tyrannosaurs ate smaller prey once they have been youthful and moved on to megaherbivores as adults. Therrien says they have been in all probability so profitable as a species as a result of “they’d advanced the power to occupy all these ecological niches throughout their very own lifespan.”

Zanno, nevertheless, disagrees. “To my thoughts,” she says, “shifting prey choice would have been too widespread amongst dinosaurian predators to completely clarify these phenomena. The dominance of tyrannosaurs in Late Cretaceous ecosystems is a fancy story now we have but to tease aside, however I do know for sure it’s an issue we are going to fortunately proceed to deal with within the years to return.”

One factor appears sure: the invention of this tyrannosaur provides astounding perception into no less than one animal. “[Although] unlucky for the juvenile tyrannosaur,” Zelenitsky says, “it’s fortunate for us that it died when it did after consuming these meals. Let’s hope extra [will be] discovered!”

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