Dinosaurs with long legs were not built for speed. Contrary to the idea that theropods like T. Rex had long limbs for speed, a new study has found that large dinosaurs evolved big legs to help them conserve energy for long walks.
Study author Thomas Holtz is a principal lecturer in the Department of Geology at the University of Maryland.
“The assumption tends to be that animals with adaptations for running, such as long legs, are adapted for a higher maximum speed, but this paper shows that there’s more to running than top speed,” said Holtz.
“When you’re a bigger animal, those adaptations may also be for endurance and efficiency. It may be about being a marathoner rather than a sprinter.”
The researchers estimated the top speeds of more than 70 theropod species based on factors such as limb proportions, size ratio, body mass, and gait.
While theropods like T. Rex weighed as much as nine tons, there were also tiny theropods that weighed less than a pound.
Some of the biggest theropods dominated the animal kingdom for 180 million years, and bipedalism and running speed were believed to be major contributors to their success. The current study, however, suggests otherwise.
The researchers determined that longer legs were associated with higher top speeds in small and medium-sized dinosaurs, but this was not the case among dinosaurs weighing over 2,200 pounds. These larger dinosaurs were not any faster than those with short legs, but they moved more efficiently.
The experts calculated how much energy each dinosaur expended while walking and found that large dinosaurs with longer legs needed less energy to move around.
“That’s actually a very beneficial savings, because predators tend to spend a great deal of their time foraging, searching for prey,” said Holtz.
“If you are burning less fuel during the foraging part of the day, that’s an energy savings that dinosaurs with shorter leg forms didn’t get.”
The findings highlight the limiting effect of large body size on running speed. The research may prompt a new investigation into what it means to be adapted for running.
The study is published in the journal PLOS ONE.