Dinosaurs actually weren't that heavy, study finds

A comparison of dinosaur skeletons with those of living mammals suggests that the ancient reptiles were tens of tons lighter than previously believed.?

By Jennifer Welsh,?LiveScience Staff Writer / June 6, 2012

Computer "skin and bones" model of Brachiosaurus. In analysis of computer models of modern mammals, they are about 20 percent smaller than the animals in real life.

Bill Sellers

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Dinosaurs have shed some extra pounds just in time for beach season, with a new analysis suggesting the mighty sauropod previously known as?Brachiosaurus?weighed tens of tons less than earlier estimates.

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Artists' renderings of dinosaurs have long been plagued by discrepancies, with some depictions larger and heftier than others.

"The whole point is we were trying to get around the guesswork" of artistic reconstructions, study researcher Bill Sellers, of the University of Manchester in the United Kingdom, told LiveScience. The researchers found that among the artists, "the ones?reconstructing their dinosaurs?as quite skinny are more right."

Skinny skeletons

To come up with their skinny dinosaur suggestion, the researchers analyzed the skeletons of living species and compared the skeletal sizes with those animals' actual weight. Using 3D images made by laser scans of full sets of bones from 14 large mammals, including a polar bear, giraffe and elephant, the researchers calculated the "minimum wrapping volume" needed to cover a skeleton with flesh.

"All we can do when we are looking at these long-dead fossil animals is rely on what we can find out from living animals," Sellers explained. They chose these large mammals instead of the dinosaur's closest relative, the?crocodile, as comparison points because they are land-adapted. (Crocodiles are adapted to living in the water, where body mass is less of an obstacle.)

Using the relationship between skeletal bones and amount of skin and fat needed, the researchers came up with a mathematical equation that also could be applied to dinosaurs. By using a computer to calculate mass, the researchers said, they took subjectivity out of the equation. In fact, when the researchers based their body-size estimates on artists' skeleton-informed reconstructions of dinosaurs, there were large discrepancies in the estimated weight. [Album: Colorful Dinosaur Art]

"They would take a scan, then produce an artistic reconstruction of the scan," Sellers said. "No two people would get exactly the same answers. Some would make them?fat dinosaurs, and some would reconstruct them as skinny dinosaurs."

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