Dreadnoughtus, announced last summer to be the largest — or at least heaviest — animal ever known to walk the earth, is under fire.
A paper published last week in Biology Letters suggests that the mass estimates may be far too high. But because the new paper uses a unique method of estimating dinosaur mass, it provides more questions than answers.
The original study used the thinnest circumference of two bones — the humerus and femur — to extrapolate total body mass, a commonly accepted method. The researchers came up with an estimate of 60 tons, or more than 132,000 pounds, and said their specimen could have been larger at maturity.
The new study involves mathematically reconstructing a “skin” volume around the bones of a dinosaur, then expanding that skin outline to account for muscle, fat and other tissues. Using this method, researchers from the University of Liverpool came up with an estimate of 40 tons, or more than 88,000 pounds.
To have the mass that was estimated last summer, the authors say, Dreadnoughtus would need to carry more than twice the volume they think it did.
“Our analysis suggests that only the lower estimates produced by previous methods are plausible,” lead author Karl Bates of the University of Liverpool’s Institute of Ageing and Chronic Disease said in a statement. “Estimates of 60 tonnes and above do not fit with our current understanding of the mass characteristics of living land animals.”
The lead author of the original study, Kenneth Lacovara, expressed skepticism about the new one.
“The method of measuring the skeleton and using it to estimate mass is based on the observation in living animals that, from a biomechanical standpoint, animals have the limbs they need — no more and no less.” Lacovara said. The new study seems to suggest that Dreadnoughtus was an exception, with massively sturdy limbs it didn’t need to support its frame.
Uncertain about size
Lacovara also said that in terms of traditional mass estimation, Dreadnoughtus is remarkably complete. Although it has just 45 percent of its skeleton (about 70 percent once reconstruction is included), it has the bones needed to estimate mass. But he’s not sure the volume of an animal’s skin can be estimated based on that number of bones. In fact, his team was quite clear in its paper on one point: The researchers weren’t certain about the overall size of the skeleton. They didn’t have its tail, its head came from another dinosaur, and so on. If any of these uncertain variables was tweaked, Lacovara said, the volume would change.
“Some artists make dinosaurs look chubby; some make them look like they’re shrink-wrapped,” Lacovara said. “Volume just isn’t preserved in the fossil record, and that’s what they’re using. Historically, scientists have worked with the data that exists, which is a pretty good policy.”
And he worries that the findings would be misleading.
“I imagine if you did this to all dinosaurs who’d had their masses estimated with traditional methods, they’d all change proportionally,” he said. “But this just makes Dreadnoughtus shrink. I’m not exactly sure how Dreadnoughtus got involved.”
