Dinosaurs wagged their tails while running, simulations reveal

Computer simulations from the Royal Veterinary College in London have suggested that bipedal dinosaurs swung their tails from side to side as they ran.

This tail motion helped them to keep their balance, for the same reason humans swing our arms. This helps to counterbalance the movement of other parts of our bodies and control angular momentum, a concept that tells us that a spinning object will continue to spin unless a force acts on it. When we’re running, we don’t want the movement of our body parts to give us an angular momentum and make us unstable, so we swing our arms to cancel it out.

The international team, which included palaeontologists, biomechanists and engineers, employed new techniques that allowed them to simulate how bipedal dinosaurs moved.

The techniques were so efficient that the simulations could be created in under half an hour on a standard laptop, while previous attempts needed the power of a supercomputer to solve the complex equations.

They simulated the movement of a small theropod dinosaur called Coelophysis, which lived 210 million years ago, and weighed around 15kg. The simulations showed that Coelophysis could run at up to 6.65 m/s(15mph), and revealed the side-to-side motion of its tail. By waving its tail, Coelophysis not only kept its balance, but also conserved energy.

“I was very surprised when I first saw the simulation results,” said lead author Dr Peter Bishop, a former postdoctoral researcher at the RVC. “After running a barrage of further simulations, including models with heavier tails, lighter tails and no tail at all, we were able to demonstrate that tail-wagging was a means of controlling angular momentum throughout gait.”

Dinosaurs in animation are sometimes shown to move their tails as they run, including in Jurassic Park and Walking with Dinosaurs. However, the researchers found that Coelophysis would actually wag its tail in the opposite direction with each step.

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To check their simulations were accurate, the team also applied them to a South American tinamou bird (Eudromia elegans), a small, ground-dwelling bird that doesn’t fly very much. The simulations were a good match for the bird’s leg movement, muscle activity and the force its foot imparts on the ground.

“These cutting-edge three-dimensional simulations show that we’ve still got much to learn about dinosaurs,” said Dr John Hutchinson, Professor of Evolutionary Biomechanics at the RVC. “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.”