For the first time, scientists have unearthed perfectly preserved stomach contents from the fossilized skeleton of a young Tyrannosaurus rex, leading them to a curious discovery about the growing beast's feeding habits. This well-preserved specimen of Gorgosaurus libratus was discovered in Canada's Dinosaur Provincial Park, a historic area where fossils of 58 different species have been unearthed so far.
But it wasn't until much later, when palaeontology staff at the Royal Tyrrell Museum spent years removing rocks from the delicate fossil, that they noticed something unusual about its structure.
On its ribs, where the soft tissue of its stomach once stood, are two bird-like hind limbs of a young Citipeselegansdinosa. However, this young carnivorous dinosaur did not seem to swallow the prey whole, but picked out the delicious "chicken legs".
While this confirms that even 75 million years ago, children flocked to chicken drumsticks on the table, it's also a very rare find. To date, fossils of about 20 species of dinosaurs with evidence of stomach contents have been identified, most of which were plant-eating dinosaurs.
Scientists believe the G. libratus was five to seven years old when it died and weighed about 335 kilograms (739 pounds). Although the weight is not light, it is only equivalent to 13% of the adult body weight.
The two C. elegans -- not to be mistaken for the tiny worms with the same scientific abbreviation -- were one-year-old urochordates that were only a year or two old and were eaten during two separate captures, perhaps days or a week apart. Although the predator was still young and capable of eating the entire carcass, it likely chose to dismember its prey and eat only the energy-dense hind legs.
At this young stage of life, the dinosaur is thought to have had streamlined heads and legs, as well as sharp teeth - all features ideal for chasing down scurrying bird-like prey. However, the fossil record shows that at about 11 years of age, the dinosaur's juvenile stage ended abruptly and the body rapidly increased in size tenfold, eventually weighing more than 3,000 kilograms (6,600 pounds).
Moreover, according to the evidence of tooth marks previously found on bones, Gorgosaurus also abandoned its favorite fleshy hind legs at this stage and began to use its new physiological weapons-a strong skull and jaws, and larger teeth to hunt giant herbivores such as Ceratopsaurus and Hadrosaurus.
It would be several million years before the dinosaurs' ultimate predator, Tyrannosaurus rex, evolved from the tyrannosaur family, but this young fossil is a fascinating glimpse into how the workings of different dietary preferences within a species can give the animal kingdom a huge competitive advantage. Scientists believe it was this intraspecific dietary variation that even facilitated their survival and was key to the evolutionary success of these giant carnivorous predators.
The researchers pointed out: "Young dinosaurs may have been a rich and reliable food source for young Gorgosaurus, which would have laid a large number of eggs." The researchers pointed out: "This change in eating habits may have allowed juvenile tyrannosaurs and adult tyrannosaurus to coexist in the same ecosystem with limited conflict."
The research was published in the journal Science Advances.