Reconsidering the Dimensions of Dinosaurs

Posted: July 6, 2009 at 1:00 am, Last Updated: July 2, 2009 at 3:34 pm

By Catherine Ferraro

Geoffrey Birchard. Creative Services photo

Geoffrey Birchard. Creative Services photo

Since the word “dinosaur” was coined in 1842 by an English biologist, these creatures have been depicted throughout popular culture in movies, books, television shows, artwork and other media. Dinosaurs have been considered the largest animals to have ever walked on Earth.

While they still maintain this status, a new study suggests that some dinosaurs may actually have weighed as little as half as much as previously thought.

Geoffrey Birchard, associate professor of environmental science and policy at Mason, was part of a team that uncovered a problem with the statistical model used by some scientists to estimate the mass of dinosaurs. The team conducted a study titled “Allometric Equations for Predicting Body Mass of Dinosaurs” and published their findings in the Journal of Zoology.

“The original equation used by scientists produces fairly accurate results when determining the mass of smaller animals, but when used on larger animals, our research shows that many errors have occurred,” says Birchard. “The new equation shows that dinosaurs are much smaller than we thought, but there is no mistaking that they were indeed huge animals.”

Developed in 1985, the original equation has been used by scientists to estimate or evaluate a variety of parameters, including brain size and egg size. The problem occurs as a result of transforming the data, which changes the properties of the original data and creates biases that can affect the predictive results obtained from the equation.

Birchard and his colleagues realized there was an error when they used the equation to determine the weight of living animals, such as a hippopotamus and an elephant, and discovered that the equation greatly overestimated the weight of these animals.

dino2The researchers developed a new equation for calculating dinosaur mass based on bone dimensions. This equation doesn’t require the transformation of data that the original equation involves.

“The best way to understand the new equation is to think about a building that is built on pillars,” says Birchard. “The bigger the building, the larger the pillars must be to support the weight of the building. In the same way, the legs of an animal are the pillars supporting its body.”

According to Birchard, this new research suggests that some dinosaurs were much more slender than had been thought. It also changes many of the characteristics scientists had already determined about dinosaurs, such as the amount of muscle required to use their bodies and how much they ate and breathed.

Birchard’s other research interests include reptilian and avian egg biology. Some of the courses he teaches at Mason include animal biology, animal physiology and dinosaur biology. In the dinosaur biology class, Birchard and his students examine both the old and new equations used to determine the mass and other characteristics of an animal.

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