Scientists discover what made a T-Rex wag its tail

Cutting-edge computer modelling has revealed some dinosaurs wagged their tails, but unlike modern dogs, this was not to show happiness but to stop them falling over.

The researchers constructed detailed computer models of the skeleton and bone structure of a small carnivorous dinosaur called Coelophysis, a 15-kilogram theropod, the same category of dinosaurs as Velociraptor and Tyrannosaurus.

Advanced computer modelling has shown bipedal theropod dinosaurs like Coelophysis wagged their tails to walk.Credit:C. Griffin

Lead researcher Peter Bishop, a Queensland Museum Network Honorary Researcher and a research fellow at Harvard University, said he and his colleagues were surprised when their model started wagging its tail.

“In all previous models of dinosaurs walking it had been implicitly assumed that the tail was just a static counterbalance for the front half of the animal,” Dr Bishop said.

“This new simulation approach was more sophisticated than previous models, we could break up different parts of the body into linked segments, which gave much greater clarity about how the animal would have actually moved.

“So we were just looking for how fast this animal could run, and the simulation had the tail wagging back and forth, left to right. We weren’t expecting that.”

Dr Bishop said the model only took into account the physical data about the body structure and was not pre-programmed with prompts about how the animal should move, indicating this was likely how bipedal dinosaurs used their tail.

The tail appeared to have swung back and forth to allow the animal to keep its balance while walking, in the same way humans swing their arms.

Dr Bishop said they had chosen Coelophysis for their modelling because at 210 million years old it was one of the earliest known theropods, so provided a good example of how they all probably moved.

“It provides a very good example of the ancestral body shape and functions of dinosaurs as a whole,” he said.

“At the end of the day physics is physics, and so we’d expect animals with the same body type such as Tyrannosaurus would move in a similar way, even though we didn’t directly model them for this paper.”

The modelling builds on Dr Bishop’s previous work comparing how dinosaurs walked with their modern equivalents in birds.

The modelling was primarily done at the Royal Veterinary College (RVC) in London, and Professor of Evolutionary Biomechanics at the RVC and co-author of the study, Dr John Hutchinson, said their simulations used modern birds for comparison.

“These cutting-edge, three-dimensional simulations show that we’ve still got much to learn about dinosaurs,” Dr Hutchinson said.

“Our results raise interesting questions about how dinosaur tails were used in a whole array of behaviours, not just including locomotion, and how these functions evolved.”

Advanced computer modelling has recently given researchers a much clearer picture of how dinosaurs would have moved, and Dr Bishop said he was excited to see what other insights could be gained.

“I won’t torture the puns too much, but we are making great strides,” he said.

“It really is astonishing when you remember that we really only have these fossilised bones to work from, and we’re able to reconstruct how these animals would have moved and lived millions of years ago.”

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