The South American dinosaur Argentinosaurus huinculensis would have had a hard time getting around. In fact, just standing up might have been difficult for the roughly 90-ton beast. When the gigantic dinosaur went extinct it left behind huge footprints and a big question: How did it move all that mass?

“This is an animal that's pushing the limits,” says biologist Bill Sellers of the University of Manchester in England. Argentinosaurus may have been the heftiest dinosaur that ever lived. As animals get larger, the increase in body mass tends to outpace the corresponding growth of muscles and bones. In the case of Argentinosaurus, a full swing of its giant thighs might have broken its bones.

Sellers and his colleagues are investigating how Argentinosaurus got around by using a supercomputer simulation of the sauropod's locomotion. The team used a laser scan of the Argentinosaurus skeleton to build a three-dimensional model of the dinosaur, which left the researchers 57 different parameters to tinker with, such as how far each joint swung and the order in which the feet took steps. The researchers then programmed a supercomputer to vary those parameters until it found gaits that demanded the least amount of energy from the animal. The simulations indicated that the dinosaur strode best when it took dainty steps at four or five miles per hour, according to a report last October in PLOS One. By staying well within the range of motion of its joints, Argentinosaurus may have avoided the pitfalls of its gigantism.

The new study's predictions agree with other lines of evidence. The simulated animal's tracks, for instance, resemble real-life fossilized footprints. And the simulations “gel with what other people have concluded based on studies looking at the shapes of bones,” says paleontologist Matt Bonnan of Stockton College. Future simulations, he adds, should also incorporate cartilage, which is lacking in fossils but which scientists can study in modern dinosaur relatives such as birds and lizards.