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 Published: 23 Sep 2021 | Last Updated: 23 Sep 2021 15:24:07

Scientists from the ÐÂÔÂÖ±²¥ discover that dinosaurs, like Tyrannosaurus and Velociraptor, wagged their tails when running, similar to how humans swing their arms when moving.

A team of researchers, led by the ÐÂÔÂÖ±²¥ (RVC), have uncovered a surprising functional similarity between dinosaur tails and human arms, despite these structures being separated by more than 300 million years of evolution. The findings reveal that bipedal dinosaurs, like the Tyrannosaurus and Velociraptor, wagged their tails from side to side when running – similar to that of humans swinging their arms back and forth during movement. This ‘wagging’ was to help angular momentum – a principle that dictates how ballerinas and figure skaters can execute pirouettes.

The study, published in Science Advances, was conducted by a team of paleontologists, biomechanists and engineers from the UK, Australia, Belgium, and the US, and represents the culmination of over three years’ work. Using sophisticated computer simulations, and leveraging new methods developed by engineers working in medicine and aeronautics, the team assessed running biomechanics in dinosaurs with tails, using two hind legs to move. This included the modelling of a small carnivorous dinosaur, Coelophysis, a 210-million-year-old theropod, weighing around 15kg.

By wagging from side to side, a bipedal dinosaur’s tail was the main regulator of angular momentum, helping to dynamically counterbalance the movement of other body parts, like the hindlimbs. Furthermore, when the tail was forced to wag out of sync with the hindlimbs, the model’s energy budget greatly increased. Just like humans, this ‘control’ of angular momentum helps to make locomotion more economical and stable.

Until now, previous studies have always treated non-avian dinosaur tails as a static, rear extension of the pelvis, acting as a counterbalance. However, this research moves beyond speculation of the tail’s importance, and mechanically demonstrates a previously unrecognised, crucial and 3D dynamic role.

Lead author Dr Peter Bishop, former postdoctoral researcher at the RVC (currently a research fellow at Harvard University, USA), commented:

“I was very surprised when I first saw the simulation results. 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.”

To ensure the reliability of their approach, the team simulated walking and running in a modern theropod dinosaur, a South American tinamou bird (Eudromia elegans, weighing about 500g). Simulations accurately replicated many important aspects of walking and running, as seen by comparing the results to previous experimental data for this species. Leg movement patterns, foot–ground forces, centre of mass fluctuations and simulated muscle activity patterns all agreed reasonably well with the experimental data, bolstering confidence in the new methodology.

Dr John Hutchinson, Professor of Evolutionary Biomechanics at the RVC and co-author of the study, further added:

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

Previous attempts at dynamic simulations of dinosaur behaviour had been limited by high computing requirements, needing the use of a supercomputer to solve the complex equations involved. But the innovative methods employed here allowed the researchers to simulate complete gait cycles in under half an hour on a standard laptop.

Study co-authors Drs Antoine Falisse, postdoctoral fellow at Stanford University, USA, and Friedl De Groote, Professor of Human Movement Biomechanics, KU Leuven, Belgium, said of the collaborative effort on the project:

“We had been developing methods for rapid computer simulations of human movements, by combining several new numerical techniques to make our simulations more than 20 times faster than previous attempts. When we were invited to see whether we could apply the same methods to simulate gaits in extinct species, we were thrilled at the opportunity and jumped on board.”

While dinosaur animators have sometimes given a little ‘wag’ to the tails of running dinosaurs in productions such as Jurassic Park and Walking with Dinosaurs, these tend to have motions opposite compared to the results obtained here.

As well as providing new insight into animal function in the distant past and helping to inform more accurate animation in future dinosaur movies and documentaries, the findings of this research are also highly relevant to applications in robotics. Development of next-generation bio-inspired robots has already drawn inspiration from the swinging tails of running cheetahs, and the new insights gleaned from Coelophysis may offer further hints for improving economy, acceleration and maneuvering performance in engineering and mechanics.

The research was funded by the European Union’s Horizon 2020 Research and Innovation program (see  for information) and Research Foundation Flanders.

Notes to Editors

Reference

Bishop, P.J., Falisse, A., De Groote, F., Hutchinson, J.R. 2021. Predictive simulations of running gait reveal a critical dynamic role for the tail in bipedal dinosaur locomotion. Science Advances: Volume 7, article abi7348.

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