Fossils show dismembered young dinosaurs in belly of T. rex cousin
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[December 09, 2023]
By Will Dunham
(Reuters) - The young Gorgosaurus knew what it liked for dinner. About
75 million years ago in what is now Canada's Alberta province, this
fearsome T. rex cousin set about hunting turkey-sized yearlings of a
feathered plant-eating dinosaur called Citipes.
With such prey numerous, the Gorgosaurus could be picky about what it
ate. It dismembered the helpless Citipes and swallowed its meaty legs
whole, ignoring the rest of the carcass.
Scientists said on Friday they have unearthed fossilized remains of a
juvenile Gorgosaurus that was 5 to 7 years old and about 15 feet (4.5
meters) long. Amazingly, it included the animal's stomach contents,
revealing its last meals.
Gorgosaurus and the more famous Tyrannosaurus, which lived several
million years later, are members of a meat-eating dinosaur group called
tyrannosaurs. This fossil has provided insight into the ecology of this
group, showing that the feeding strategy and diet of tyrannosaurs
changed dramatically during their lifespan. This is the first
tyrannosaur skeleton with prey items preserved inside its stomach.
Based on tooth marks left on bones, adults are known to have hunted big
plant-eating dinosaurs.
"Adult tyrannosaurs were well-equipped for seizing and killing large
prey, like duckbilled dinosaurs and horned dinosaurs. Their skulls and
teeth were capable of withstanding the major torsional stresses
associated with biting and holding onto large prey," said François
Therrien, dinosaur palaeoecology curator at the Royal Tyrrell Museum in
Alberta and co-leader of the study published in the journal Science
Advances.
![](http://archives.lincolndailynews.com/2023/Dec/09/images/ads/current/debbiesfloral_lda_112023.png)
"In contrast, the weaker bites and teeth of young tyrannosaurs were
ideal for slashing bites, not holding onto prey. They would have been
well-equipped for hunting smaller dinosaur species and young dinosaurs,"
Therrien added.
The study indicates that tyrannosaurs occupied different ecological
niches during their lifespan: "mesopredators" - mid-size predators -
while young, becoming apex predators as adolescents and adults. That
means juvenile tyrannosaurs did not compete with their elders for the
same prey.
"Young tyrannosaurs had blade-like teeth, lightly built skulls,
relatively weak bites, long legs and appeared more 'athletic' than adult
tyrannosaurs, which were very robustly built, had massive skulls,
thicker teeth - often described as 'killer bananas' because of their
shape - and powerful bites that allowed them to crush bones," Therrien
said.
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![](../images/120923PIX/news_h15.jpg)
The fossilized 75 million year old skeleton of a juvenile
Gorgosaurus, a meat-eating dinosaur that lived during the Cretaceous
Period in what is now Canada's Alberta province, with the left view
showing the location of stomach contents hindlimbs of a small
dinosaur called Citipes, is seen in this picture obtained by Reuters
on December 7, 2023. Royal Tyrrell Museum of Palaeontology/Handout
via REUTERS
![](http://archives.lincolndailynews.com/2023/Dec/09/images/ads/current/bennet_lda_010722.png)
Gorgosaurus, a bit smaller than Tyrannosaurus, ruled its ecosystem.
It walked on two legs, had short arms with two-fingered hands, a
massive skull three feet (one meter) long, reached 30-33 feet (9-10
meters) in length and weighed 2-3 tons. This juvenile Gorgosaurus
weighed about 730 pounds (330 kg), with a skull around 20 inches (50
cm) long.
The fossil was unearthed at Dinosaur Provincial Park in southern
Alberta. The region during the Cretaceous Period was a forested
coastal plain near the western shore of a vast inland sea that split
North America into two halves.
The stomach contents, found between the ribcage and hip bones,
included the leg and foot bones of two Citipes yearlings. Citipes
was a small, birdlike dinosaur that walked on two legs and had a
head resembling a parrot.
"Since the Citipes would have had large broods laying some 30 eggs
in a nest, their hatchlings would have been abundant in the
ecosystem and ripe for the picking by young tyrannosaurs," said
University of Calgary dinosaur paleontologist and study co-leader
Darla Zelenitsky.
Based on the differing stomach acid damage to the Citipes bones, the
yearlings were eaten at different times, and the Gorgosaurus died
from unknown causes hours or days after its last meal.
"The bones found in the stomach are entire legs. Maybe a full
Citipes was too large to pass through the throat of a young
Gorgosaurus, so the predator selectively dissected away the meatiest
parts of the carcass. This Gorgosaurus was fond of drumsticks,"
Zelenitsky said.
"Whereas adults were more indiscriminate feeders, eating all parts
of a large herbivore's carcass - often pulverizing and swallowing
bones in the process - young individuals were far more surgical in
how they fed," Zelenitsky added.
(Reporting by Will Dunham in Washington, Editing by Rosalba O'Brien)
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