Call it a downsizing of dinosaurian proportions. Last year, scientists described the near-complete fossil of a gigantic species of long-necked sauropod called Dreadnoughtus schrani. Using the dimensions of its leg bones and a formula that projected weight-carrying capacity, they estimated that the massive herbivore tipped the scales at about 59 metric tons, making it the heftiest dinosaur known from a relatively complete specimen. But now, a new analysis casts significant doubt on the previous weight estimate. The new team took a digital model (seen at three angles, above) to determine the weight of the bones and then added 21% more volume to account for flesh and other soft tissue outside of the skeleton. (Modern-day mammals have an average soft tissue volume that is 21% greater than their skeletal volume, the researchers say.) After cutting the dinosaur’s weight to account for lung space, the researchers report today in Biology Letters that Dreadnoughtus weighed a little less than 28 metric tons. But even when researchers boosted the volume of tissue outside the dino’s torso by an unusually large 50% and doubled the size of every other body part, the creature still weighed in at only 38 metric tons. So why did the previous estimate run so high? One possibility, the researchers say, is the technique previously used is based on the weight-carrying capacity of adult bones. The only known specimen of Dreadnoughtus—analyzed in both studies—was an adolescent, whose bones may have been disproportionately large compared with the rest of its body.
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