A new method of estimating the weights of large-bodied animals hints that some dinosaurs may have been considerably lighter than scientists realized. When using the technique, researchers first use lasers to scan a skeleton of a large animal (example, left) and then software to estimate the minimum volume of tissue needed to fill the creature's body cavities and then cover its bones and skull. Next, the team adds an extra 21% to that volume, a correction factor that primarily includes limb muscles but also accounts for skin and surface flesh. (The 21% adjustment is derived from measurements of 14 living species of large-bodied mammals ranging in size from wild boar and caribou to giraffes and elephants and is remarkably consistent from one species to another, the researchers note.) Finally, multiplying the presumed volume of the creature by the average density of body tissue—another factor derived from modern-day mammals—provides an estimated weight, the researchers report online today in Biology Letters. When the technique was applied to the long-necked herbivore Giraffatitan brancai (3D model of skeleton, right), the team found that the dinosaur—one of the largest species yet known, reaching an estimated length of 26 meters—likely weighed just a little over 23 metric tons. That's hefty indeed, but it's nowhere near some of the previously reported weight estimates for the species, which range as high as 80 metric tons.
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