Dinosaurs, already known for having small brains, were in fact total airheads, a new study suggests.

Ohio University researchers discovered via CT scans that dinosaurs, particularly predators such as the Tyrannosaurus rex, had more air cavities in their skulls than scientists once thought.

The CT scans showed that the amount of air space was considerably greater than brain cavity material.

However, those pockets of, essentially nothing, appear to have served an important function for the giant prehistoric beasts.

The air space may have lightened the load of the head, perhaps making it as much as 18 per cent lighter than it would have otherwise been.

The savings in weight could have allowed the predators, who weighed more than 1,100 pounds, to gain more muscle mass (more bone mass requires a lot of energy to maintain) or to take on larger prey.

"Scientists have tended to focus on things such as bones and muscle, and ignored these air spaces," researcher Lawrence Witmer, a paleontology professor, said in a news release. "If we're going to decipher the mysteries of these extinct animals, maybe we need to figure out just why it is that these guys were such airheads."

The findings are published in a recent edition of The Anatomical Record.

The CT scans of the T. rex and its fellow predator, the Majungasaurus, showed a large, arching airway that went from the nostrils to the throat, as well as many sinus cavities.

The sinus cavities may have made the bones in the head more hollow, like the hollow beams used in construction that are strong but do not weigh as much as solid beams.

A lightweight yet strong skull likely allowed the predators to move their heads more quickly, as well as made it easier for them to hold their heads up on their long, cantilevered necks.