Juvenile tyrannosaurs hunted baby dinosaurs as part of their diet

A recent discovery sheds light on the dietary habits of a juvenile tyrannosaur, revealing its last meal to be two baby dinosaurs. This finding offers a rare glimpse into the life and development of these prehistoric creatures.

In the Alberta Badlands, a hotspot for dinosaur hunters, a remarkable fossil was unearthed in 2009. It was the ribcage of a juvenile gorgosaurus, a close relative of the T. rex.

Juvenile gorgosaurus

After meticulous preparation, researchers at the Royal Tyrell Museum of Palaeontology discovered the remains of two small bird-like dinosaurs, known as citipes, inside the ribcage.

The juvenile gorgosaurus, about seven years old and weighing approximately 330kg, was in a developmental stage equivalent to a human teenager. Its size was roughly a tenth of a fully grown adult tyrannosaur. 

Tyrannosaur dietary shifts

The presence of the citipes’ hind limbs within its ribcage is “solid evidence that tyrannosaurs drastically changed their diet as they grew up,” according to Dr. Darla Zelenitsky from the University of Calgary.

The findings highlight a significant shift in the feeding habits of tyrannosaurs as they matured. 

“We now know that these teenage (tyrannosaurs) hunted small, young dinosaurs,” explained Dr. Zelenitsky. 

Dr. Francois Therrien described these adult tyrannosaurs as “quite indiscriminate eaters.” They probably pounced on large prey, “biting through bone and scraping off flesh,” he told BBC News.

But, these immature tyrannosaurs were probably not ready to jump into a group of horned dinosaurs, where the adults weighed thousands of kilograms, said Dr. Zelenitsky.

Selective eaters

Interestingly, researchers found only the legs of the baby dinosaurs inside the gorgosaurus. This suggests that the young tyrannosaur was selective, possibly preferring the meatiest parts.

“The rock within the ribcage was removed to expose what was hidden inside,” explained Dr. Therrien. “And lo and behold – the complete hind legs of two baby dinosaurs, both under a year old.”

Dr. Zelenitsky said that the teenage gorgosaurus seems to have wanted the drumsticks – probably because that’s the meatiest part.

“This animal was selecting and even dissecting its prey – biting off the legs and swallowing them whole.”

Physical transformations of tyrannosaurs

As tyrannosaurs grew, they underwent significant physical transformations. Juveniles were lighter and had blade-like teeth, whereas adults developed rounder teeth, dubbed “killer bananas” by Dr. Therrien. 

This change in dentition reflects a shift in feeding strategy from selective predation in juveniles to a more powerful and indiscriminate approach in adults.

The discovery provides a window into the lives of these ancient creatures, debunking the stereotype of dinosaurs as mindless monsters. 

Professor Steve Brusatte is a palaeontologist from the University of Edinburgh. He said that seeing prey in the dinosaur’s guts gave a real insight into the animals. “They weren’t just monsters, they were real, living things and pretty sophisticated feeders.”

In the 1993 film Jurassic Park, a giant T. rex chased a car through a fictional theme park. Professor Brusatte noted that an adult T. rex wouldn’t have chased after a car – its body was too big, and it couldn’t move that fast.

“It would be the youngsters – (like this gorgosaur) – the children of T. rex that you’d have to keep an eye on.”

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