Some Dinosaurs Wagged Their Tails When Running, Just Like Humans Swing Their Arms

Artist impression of Coelophysis. Image Credit: Daniel Eskridge/

The tail of bipedal dinosaurs was more than just a counterbalance for their heads. New 3D gait simulations suggest that the tail played a more pivotal and dynamic role: It would swing rhythmically went they were walking and running, just like how humans swing their arms when moving.

According to the new study in Science Advances, the tail movement was the main regulator of the bipedal dinos' angular momentum. Scientists had assumed the large tails of therapods were a static counterbalance to prevent them from toppling over, and focused more on studying their legs to understand how they moved. This new study shows that tails are actually dynamic; a fundamental part of the dinosaurs' ability to walk and run.

The study employed the most sophisticated simulations to model how these extinct reptiles might have moved across the surface of our planet. The team looked specifically at the Triassic Coelophysis bauri, a 210-million-year-old therapod that weighed about the same as a coyote. The simulations show that the tail was not just a rear extension of the pelvis but was crucial for motion.

“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,” lead author Dr Peter Bishop of Harvard University said in a statement.

Previous attempts at simulating dinosaurs' walking gaits with computers have been limited by the power of those computers. Walking motion might not seem particularly difficult but the equations that govern it are far from easy. New methods to improve these calculations were key and they were demonstrated in living animals, including humans.

“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,” co-authors Dr Antoine Falisse and Professor Friedl De Groote added.

Computer simulations of running locomotion in a modern tinamou bird (top) and extinct theropod dinosaur Coelophysis (bottom). Image credit: Tinamou photograph by M. Perez (, Coelophysis skeleton photograph by C. Griffin.

If tails are not static, then their role might extend further than walking and running, which the team is keen on investigating next. In popular media, dinosaur tails have often been given a little wag, but the simulation highlights that the swing seen in movies and TV shows like Jurassic Park or Walking with Dinosaurs is actually going in the opposite direction to the results seen here. Jurassic World 3, take note.


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