The last meal of the tyrannosaurus was two small dinosaurs

  • By Victoria Gill
  • Science Correspondent, BBC News

image source, Royal Tyrrell Museum of Palaeontology

Image caption,

Dr. Darla Zelenicki and Dr. Francois Therrien with the complete Tyrannosaurus fossil

Scientists have discovered the last meal of a 75-million-year-old tyrannosaurus – two small dinosaurs.

Researchers say the animal’s preservation — and the small, hapless creatures it ate — sheds new light on how these predators lived.

This is “solid evidence that tyrannosaurs drastically changed their diet as they grew,” said Dr. Darla Zelenicki of the University of Calgary.

The specimen is a young Gorgosaurus – a close cousin of the giant T. rex.

image source, BBC/Royal Tyrrell Museum of Palaeontology

This particular Gorgosaurus was around seven years old – the equivalent of a teenager in terms of development. It weighed about 330 kg when it died – about one-tenth the weight of a fully grown adult.

Below its ribcage are the hind limbs of two small bird-like dinosaurs called sitipes.

image source, Julius Chotoni

Image caption,

The young Gorgosaurus would have chased down small therapods and ‘sliced’ them with its blade-like teeth

A wealth of earlier fossil evidence, including apparent bite marks on the bones of larger dinosaurs that match the teeth of tyrannosaurs, has allowed scientists to build a picture of how the three-ton adult Gorgosaurus attacked and ate very large herbivorous dinosaurs that they lived in herds.

Dr Francois Therrien of the Royal Museum of Palaeontology in Tyrrell described these adult tyrannosaurs as “absolutely indiscriminate eaters”. They probably pounced on large prey, “biting the bones and scraping the flesh,” he told BBC News.

But Dr. Zelenicki added that “these smaller, immature tyrannosaurs probably weren’t ready to jump into a group of horned dinosaurs where the adults weighed thousands of kilograms.”

“Toes pierce the chest”

The fossil was originally discovered in the Alberta badlands in 2009 – a hot spot for dinosaur hunters.

Buried in rock, it took years to prepare and it wasn’t immediately obvious that there was loot inside. Staff at the Royal Tyrrell Museum of Paleontology in Alberta eventually noticed small toe bones protruding from the thorax.

“The rock in the chest was removed to reveal what was hidden inside,” explained Dr. Therrien, who is the other lead scientist on this study. “And there you have it – the full hind legs of two baby dinosaurs, both under a year old.”

Dr Zelenicki said finding only the legs suggested this teenage gorgosaurus “appears to have wanted the thighs – probably because that’s the meatiest part”.

image source, Royal Tyrrell Museum of Palaeontology

Image caption,

Adult Gorgosaurus grew to ten times the size of this 300-pound juvenile

Gorgosaurus is a slightly smaller, more ancient species than T. rex. Fully grown, these were – as Dr Therrien put it – “big, tough tyrannosaurs”.

They transformed as they matured. “The juveniles were much more lightly built – with longer legs and very blade-like teeth,” he explained. “The adult teeth are much more rounded – we call them ‘killer bananas.’

“This specimen is unique – it is physical evidence of the very different feeding strategy of the young.

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

image source, Royal Tyrrell Museum of Palaeontology

Image caption,

Tyrannosaurus skull and blade-like teeth

Professor Steve Brusat, a palaeontologist from the University of Edinburgh and the National Museum of Scotland, said seeing prey in a dinosaur’s gut gave a real insight into the animals: “They weren’t just monsters, they were real, living creatures and beautiful complex feeders.”

Recalling an image of a T. rex in the 1993 film Jurassic Park – where the giant dinosaur chases a car through the fictional theme park – Prof Brusatte added: “A big adult T. rex wouldn’t be chasing a car – if there were cars or SUVs then – its body it was too big and couldn’t move that fast.

“It will be the young… [like this gorgosaur] – the T. rex kids to keep an eye on.”

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