Dinosaurs may have been able to run with one foot on the ground like emus

If you want to imagine a dinosaur running, just look at an emu, which probably has a similar stance and is most energy efficient at running at medium speeds with one foot on the ground.

Pascha van Bijlert of Utrecht University in the Netherlands and his colleagues wanted to understand why birds run so differently from humans.

For example, emu (Dromaius novaehollandiaeThe 50 kilometre-per-hour dinosaur (S. palustris) kept one foot on the ground at all times when running at medium speeds, a method thought to require far more energy than the “aerial” running style used by other bipedal animals, such as humans, in which both feet leave the ground at the same time.

To learn more, the scientists built a computer model based on the emu and used physics simulations to measure the energy output of different running styles while varying the bird’s anatomy.

“These are changes that aren’t possible in real birds, but they represent differences between different bird species,” van Bilgert says. “For example, quails are very crouched and probably don’t have a lot of energy stored in their tendons. Emu’s are relatively upright, but they do have a lot of energy stored in their tendons.”

We tend to think of running as always having an aerial phase, says van Bilgert, “but[for emus]it goes like this: walking, ground running, aerial running, so they have an additional running style at intermediate speeds. Ground running seems to be the more wasteful running style because it uses more energy than aerial running.”

But in some cases, he says, running with the ground on the ground can optimize energy use: “The muscles are strongest in a very crouched position, and there is a range of running speeds where running with the ground on the ground is actually the best option when an upright position is not possible. Humans don’t do this because they can stand upright, but birds can’t.”

Fossil evidence suggests that some dinosaurs adopted a posture similar to that of large, running birds living today. Velociraptor and Deinonychus Van Biljelt said it had a relatively thin tail and long, feathered forelimbs, which shifted its centre of gravity forward and gave it a more crouched posture, which he said is similar to that of an emu.

“When explaining dinosaur migration to people who haven’t really given it much thought, I like to jokingly say that the closest relative non-avian theropod dinosaur would be the crocodile-tailed emu.”

Jacqueline Nguyen from the Australian Museum in Sydney said the researchers’ model had allowed them to carry out virtual experiments that could yield new insights.

“The authors suggest that avian terrestrial locomotion may have evolved for the first time among non-avian dinosaurs,” Nguyen said. “This mode of locomotion may have been another feature that birds inherited from their dinosaur ancestors, such as bipedalism and modified leg bones and feathers.”