A remarkable fossil preserving the last meal of a young tyrannosaurus has been discovered in Canadawhich revealed that the dinosaur had a taste for prehistoric fast food.
While tyrannosaurs were among the most fearsome dinosaurs to roam the planet, with adults boasting massive bodies, large heads and bone-crushing bites, juveniles were rather weaker, with long, skinny legs, blade-like teeth and narrow skulls.
The transformation was long thought to be associated with a shift in diet as the tyrannosaurs matured and required more energy: while evidence, including bite marks on bones, suggested that adults hunted and feasted on enormous herbivores, such as duckbills and horned dinosaurs, juveniles lacked the dental apparatus to tackle such prey.
But just what the youths indulged in was something of a mystery.
Now a spectacular fossil containing the preserved stomach contents of a young tyrannosaurus has provided a rare insight into their diet.
“This is really the first solid evidence we have of what the diet or feeding behavior was in a young tyrannosaurus,” said Dr Darla Zelenitsky, the co-author of the study room at the University of Calgary.
Thought to be about 75m years ago, the fossil of the young Gorgosaurus libratus was discovered in the badlands of Dinosaur Provincial Park, Canada in 2009 by Darren Tanke, a technician working at the Royal Tyrrell Museum of Paleontology.
The team say the young tyrannosaurus weighed around 350kg, with analysis of growth rings in the fossilized bones suggesting it died young, at five to seven years old.
But it didn’t starve.
“It was during the preparation process at the end of 2010 that Darren noticed small knuckle bones protruding from the rib cage of the tyrannosaurus,” said Dr François Therrien, the curator of dinosaur palaeoecology at the Royal Tyrrell Museum and co-author of the research said. .
The team wrote in the journal Science Advances that inside the rib cage they discovered the remains of two young citypes: turkey-sized creatures with a parrot-like head that would have been quick on their feet, rather like an emu.
Differences in the extent of gastric acid damage suggested that the citypes were consumed in two separate sittings. However, the remains were largely limited to the hind legs, suggesting that the young tyrannosaurus did not eat all of its prey.
“This young tyrannosaur seems to have had an appetite for citipes drumsticks,” Zelenitsky said, adding that one possibility is that the bones were the meatiest part of the prey, with the skull of the young gorgosaurus allowing for precision feeding .
While the team said it was unclear how the tyrannosaurus died, it appeared to have perished within a week of its last meal.
The discovery is the first time that the fossil of a tyrannosaurus has been found with the contents of its stomach preserved. And there is another bonus to the find.
“The bones present in the stomach represent the most complete citipes skeleton known,” Therrien said.
Prof Stephen Brusatte, a palaeontologist at the University of Edinburgh, who was not involved in the work, said the fossil was direct evidence of what a tyrannosaurus was eating.
“Not guesswork or a series of assumptions based on interpretation of bite marks or coprolites – fossil feces – but actual direct in-the-gut evidence,” he said. “This is a tyrannosaur’s last meal, preserved in stone.”
Brusatte said the fossil supports the idea that tyrannosaurs changed their diet as they aged, from small to large prey.
While Brusatte added that the insights make intuitive sense, he said it’s not inevitable, noting an alternative possibility is that young tyrannosaurs simply feasted on prey killed by adults.
“But that doesn’t seem to be the case here – the small tyrannosaurs ate small prey, so they probably actively hunted their own food and changed the prey they targeted as they got bigger,” he said. “This means that tyrannosaurs filled different roles in the food web as they grew up, which is pretty neat.”
