When bipedal dinosaurs walked, they probably strode with a swagger, swishing their tails up and down for the same reason humans swing their arms when they walk.
Traditionally, dinosaur tails have been seen as a counterbalance for the weight of a dinosaur’s head. But and Peter Bishop at the Royal Veterinary College in London say the tail probably played a more active role in a dinosaur’s gait. With every step, the tail would swing up and down to regulate the dinosaur’s angular momentum and increase its walking efficiency.
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This comes from a computer simulation of Coelophysis bauri, a bipedal dinosaur that lived between about 220 to 195 million years ago. Hutchinson and Bishop and their colleagues designed the simulation as part of an ongoing research project aimed at better understanding the locomotion of early dinosaurs.
To build an accurate biomechanical model of a long-extinct species, the team first turned to modern birds called tinamou (for instance a species called ), which are small birds that prefer running to flying. By grafting a virtual model of a tinamou’s musculature onto a computerised version of its skeleton, the simulation was able to accurately replicate the tinamou’s gait. Hutchinson and Bishop then applied the simulation to the muscular and skeletal structure of C. bauri.
The simulation didn’t perform exactly as expected. “Looking closely,” says Hutchinson, “we realised the tail was doing some rather funny stuff.” Instead of statically extending backward as expected, the tail was an active participant in locomotion. With every step, it would bob up and down twice and swing left and right once, matching the head and leg movements.
To understand the role the tail was playing, the team deleted the tail from their computer model. When this happened, they found that the rest of the dinosaur’s muscles had to work 18 per cent harder to maintain a consistent running speed, suggesting that the tail’s movements made for more efficient steps.
“By understanding how real, living animals work, we can make better inferences about how extinct ones worked,” says Hutchinson.
Science Advances
Article amended on 23 September 2021
We corrected Peter Bishop’s name
