New analysis cuts massive dino’s weight in half

Dreadnoughtus maybe wasn’t as dreadful as original estimates suggested

drawing of gigantic dinosaur Dreadnoughtus schrani

SIZE CHECK  The gigantic dinosaur Dreadnoughtus schrani may not have weighed as much as scientists thought. A new analysis of bone volume puts the dino’s weight at as little as 22,000 kilograms.

Jennifer Hall

One of the world’s heaviest dinosaurs may be getting demoted to a lower weight class.

Dreadnoughtus schrani, an herbivore known for its record-breaking mass of 59,300 kilograms, probably weighed only about half as much, scientists conclude in a new analysis published online June 9 in Biology Letters.

The famous dinosaur may have been a little bit bigger than Apatosaurus — but not much, says study coauthor Karl Bates, a biologist at the University of Liverpool in England.

“It’s not the sort of game-changing massive difference that it was built up to be,” he says.

Last year, paleontologist Kenneth Lacovara of Drexel University in Philadelphia and colleagues estimated Dreadnoughtus’ mass by plugging thigh and arm bone circumferences into an equation (SN Online: 9/4/14). But they didn’t factor in the possibility for error in their answer, Bates says.

reconstruction of d. schrani dinosaur skeleton
THICK AND THIN A 3-D model of Dreadnoughtus schrani helped researchers estimate the dinosaur’s body volume (light blue, respiratory volumes shown in black) and then calculate the animal’s mass. According to a new calculation, the dinosaur may have been a lot thinner (top) than scientists originally estimated (bottom). K.T. Bates et al/Biology Letters 2015 (CC BY 4.0)

Bates and colleagues tried a different method. They used a computer program and measurements from living animals to estimate Dreadnoughtus’ volume, and then calculated the dinosaur’s mass. Their answer puts Dreadnoughtus somewhere between 22,000 and 38,000 kilograms.

Lacovara isn’t convinced. Bates’ method relies on a lot of guesswork, he says. Scientists don’t have a complete Dreadnoughtus’ skeleton — only about half of the bones were preserved.

So the new study’s authors had to guess the dinosaur’s skeletal proportions, as well as how chubby Dreadnoughtus was and the volume of its respiratory system. Even a small change in skeletal length, for example, could vastly change the animal’s body volume, Lacovara says.

In contrast, all his team did was “walk up to two bones with a tape measure and take a measurement. So there was zero opportunity for subjectivity,” he says.

“We’re never going to be able to put Dreadnoughtus on a scale,” Lacovara says. But for estimating the mass of land animals that walk on four legs (including mammals and reptiles), the equation his team used “has generally been considered the gold standard.” 

Meghan Rosen is a staff writer who reports on the life sciences for Science News. She earned a Ph.D. in biochemistry and molecular biology with an emphasis in biotechnology from the University of California, Davis, and later graduated from the science communication program at UC Santa Cruz.

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