Two-legged dinosaurs may have swung their tails as they crashed through the undergrowth – just like humans swing their arms – according to scientists who have modelled their movements in 3D at Harvard University.
Until now, it was widely believed that bipedal (two-legged) dinosaurs grew long tails to counterbalance the weight of their heads, and the tail was merely a rigid extension of the pelvis. But it is now thought that swinging their tails reduced the muscular effort required to propel themselves forwards, meaning they could run faster.
To better understand how Coelophysis bauri – a small, meat-eating dinosaur that relied on speed and agility to catch its prey – might have moved based on its physiology, Peter Bishop at the Harvard Museum of Comparative Zoology, US, and colleagues constructed a 3D simulation using CT scans of dinosaur bones and digital models of how the skeleton would have fitted together.
Crucially, this simulation enabled them to predict which movement patterns would have maximised certain goals, such as running faster. And the impact of altering or removing certain body segments, such as the tail. The simulations unexpectedly revealed that the dinosaur made pronounced movements with its neck and long heavy tail as it moved.
“It is not like a dog wagging its tail when it is excited. It is a modest wag, but it is very precisely timed with the forwards and backwards swinging of the legs,” said Bishop, whose research was published in Science Advances. “Just as we humans swing our arms when we’re walking or running, we think it’s about balancing and counterbalancing the movement of the other body segments.”
The team also investigated the impact of removing the tail: doing so meant that the simulated dinosaur had to apply 18% more muscle effort as it moved, suggesting that the tail may also have reduced Coelophysis’s energy expenditure – another reason why humans swing their arms when they walk.
“When we chopped the tail off, the dinosaur was effectively having to wag its hips to compensate for the loss of the tail,” Bishop said.
He believes the findings could also inform how other two-legged dinosaurs, including giants such as Tyrannosaurus rex, moved. “These simulations give us a much better understanding of what these creatures were like as living animals, which enables us to build up a better picture of the history of life, and an appreciation of how we got to the animals and plants we have today,” said Bishop.
Understanding these unique, extinct body plans could also provide inspiration for new and more efficient types of robots, he added.