Life and death in real-life Jurassic Park

Dr Darla Zelenitsky and Dr Francois Therrien with their fossil
Dr Darla Zelenitsky and Dr Francois Therrien with their fossil - The Royal Tyrell Museum of Palaeontology/Reuters

A tyrannosaur’s last meal was two baby dinosaurs, the study of a 75 million-year-old fossil has revealed.

Its remains have been discovered inside the fossil of the extinct predator, shedding fresh light on its changing diet.

The hind limbs of two small bird-like dinosaurs called citipes were found beneath the rib cage of a juvenile Gorgosaurus, which is closely related to the Tyrannosaurus rex, according to a study published in the journal Science Advances.

Research suggests a juvenile Gorgosaurus preyed on small, young dinosaurs, while earlier fossil evidence showed the adult Gorgosaurus attacked and ate very large plant-eating dinosaurs which lived in herds.

This gorgosaur was about seven years old, equivalent to a teenager in terms of its development and it weighed about 330kg when it died, which is about a 10th of the weight of a fully-grown adult.

Tyrannosaurids were large carnivorous dinosaurs that underwent major changes in skull robusticity and body proportions as they grew.

Dr Darla Zelenitsky, one of the lead scientists in the study, told the BBC the discovery is “solid evidence that tyrannosaurs drastically changed their diet” as they aged.

Dr Zelenitsky said: “We now know that these teenage (tyrannosaurs) hunted small, young dinosaurs.These smaller, immature tyrannosaurs were probably not ready to jump into a group of horned dinosaurs, where the adults weighed thousands of kilograms.”

A juvenile Gorgosaurus feeds on its prey
A juvenile Gorgosaurus feeds on its prey - Royal Tyrrell Museum of Palaeontology/Reuters

The fossil was originally found in Canada’s Alberta Badlands in 2009, but was entombed in rock and took years to be prepared for study. Earlier fossil evidence, including bite marks on the bones of larger dinosaurs that match tyrannosaur teeth, have allowed scientists to build a picture of how the three-tonne adult gorgosaurs attacked and ate very large plant-eating dinosaurs.

Dr Francois Therrien, from the Royal Tyrrell Museum of Palaeontology who is also leading the study, said adult tyrannosaurs were “quite indiscriminate eaters’’. He told the BBC they likely pounced on large prey, “biting through bone and scraping off flesh”.

He added: “The rock within the rib cage was removed to expose what was hidden inside. And lo and behold, the complete hind legs of two baby dinosaurs, both under a year old.”

Dr Zelenitsky said that finding “complete hind legs of two baby dinosaurs, both under a year old” suggested that this teenage Gorgosaurus “seems to have wanted the drumsticks – probably because that’s the meatiest part”.

She said: “This specimen is unique – it’s physical proof of the juveniles’ very different feeding strategy.”

While the adults bit and scraped with their powerful “killer banana” teeth, “this animal was selecting and even dissecting its prey – biting off the legs and swallowing them whole”.

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

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