Stegosaurus ‘Sophie’ Weighted 1,600kg, Say UK Scientists

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British scientists have worked out the weight of the world’s most complete specimen of a Stegosaurus dinosaur that dates back to 150 million years. The beast is easily recognizable because of a row of sharp bony plates along its spine. Researchers at the Natural History Museum and Imperial College London calculated the extinct creature’s body mass to get an accurate measurement.

Sophie was a young adult Stegosaurus

Scientists found that the Stegosaurus weighted 1,600kg, almost similar in size to a small rhino. The specimen, nicknamed ‘Sophie,’ aged only six or seven when it died. Despite its nickname, scientists don’t know whether Sophie was male or female. Sophie was found in Wyoming, U.S., in 2003 with more than 80% of its skeleton intact.

Scientists said Sophie was only a young adult Stegosaurus, equivalent to a human teenager, when it died. Had it survived into adulthood, it would have tipped the scale at more than 3,000kg. Dr Charlotte Brassey, the lead author of the study, said that knowing its body mass was critical to finding out its metabolism, growth rates, and feeding requirements. Researchers are glad that they got hold of the body mass so early on.

How researchers calculated its body mass

There is little evidence of how it died. Scientists say it might have fallen into a shallow pond where it was quickly buried. It helps explain why the specimen was so well-preserved. Scientists scanned all 360 bones of the Stegosaurus before putting it on display. Traditionally, body mass of animals is estimated from the circumference of the thigh bone and upper arm.

But Sophie was an exceptional case because it was mostly complete. Researchers led by Dr Brassey created 3G models of the whole fossil, including all the bones. Then they wrapped simple shapes around its body outline, and used the whole volume to estimate the body mass. Separately, they also took the circumference of the thigh bone and compared it to a modern animal of similar size. Both methods yielded matching estimates for the Stegosaurus’s body weight.

Findings of the study were published in the journal Biology Letters.

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