Monkeys use it to cling to branches, cats to balance themselves.
But what is the use of the tail of bipedal dinosaurs, those who walk on two legs like us?
American researchers at Harvard have modeled the movements of these animals which disappeared 66 million years ago, in order to unravel this mystery.
Their work has just appeared in the scientific journal Science Advance, Thursday, September 22.
The tails of dinosaurs are often considered to counterbalance their heavy heads, and allow them to remain upright, in a static manner.
This is not the main part of its role: in reality, this extension of their body allows them to go faster, and to save energy.
Without a tail, bipedal dinosaurs must exert 18% more effort, according to the study's results.
As the dinosaur's left leg moves forward, the tail moves to the right.
And vice versa.
One way to save energy.
To arrive at these conclusions, the researchers studied the fossilized bones of dinosaurs. Some wear indicates repetitive movement throughout the life of the animal. Their position says a lot about the movements he performs. Scientists have also observed fossilized footprints. If the trace is deeper on the outside, this suggests, for example, that the dinosaur was leaning on this side.
These vestiges of a bygone era make it possible to partially reconstruct the movements of dinosaurs.
To verify that this is not a misinterpretation, the authors of the study compared their results with the observation of birds that do not fly or little.
These have similar musculoskeletal behavior.
But they don't have a tail.
All of these clues, entered into a computer program, make it possible to obtain a 3D model that scientists consider to be quite accurate.
A more energy-efficient walk, like that of man
“When the dinosaur's left leg moves forward, the animal's center of gravity shifts.
If, at the same time, it moves its tail to the right, it corrects its position.
This prevents him from providing other muscular efforts, ”explains Peter Bishop, researcher at Harvard and co-author of the study.
And the faster the dinosaur goes, the more it intensifies this movement.
"A way of moving that we find in humans, in a certain way", marvels the scientist.
For the same reasons, in fact, we move our arms in reverse of our legs.
“This form of movement is relatively passive.
It does not require significant muscular effort.
This approach was therefore imposed naturally, ”explains Peter Bishop.
“It's interesting that some bipedal dinosaurs, like therizinosaurs, had shorter tails but much longer arms, and we wonder if they didn't use the arm swing to walk and run more efficiently… An idea that will have to await further studies, ”concludes Peter Bishop.