University of Manchester biologists used lasers to measure the minimum amount of skin requisite to enfold around the skeletons of modern-day mammals, including reindeer, polar bears, giraffes and elephants.
They exposed that the animals had almost exactly 21% more body mass than the minimum emaciated 'skin and bone' wrap volume, and applied this to a giant Brachiosaur skeleton in Berlin's Museum für Naturkunde.
Previous estimates of this Brachiosaur's weight have varied, with estimates as high as 80 tonnes, but the Manchester team's calculations published in the magazine Biology Letters abridged that figure to just 23 tonnes. The team says the new method will apply to all dinosaur weight capacity.
Direct author Dr Bill Sellers said: "One of the most important things palaeobiologists require to know about fossilized animals is how much they weighed. This is astonishingly difficult, so we have been testing a new approach. We laser scanned various large creature skeletons, including polar bear, giraffe and elephant, and calculated the minimum packaging volume of the main skeletal sections.
"We showed that the actual volume is reliably 21% more than this value, so we then laser scanned the Berlin Brachiosaur, Giraffatitan brancai, calculating the skin and bone packaging volume and added 21%. We found that the giant herbivore weighed 23 tonnes, sustaining the view that these animals were much lighter than usually thought.
Dr Sellers, based in Manchester's Faculty of Life Sciences, explained that body mass was a critical limit used to constrain biomechanical and physiological traits of organisms.
He said: "Volumetric methods are becoming more common as techniques for estimating the body masses of fossil vertebrates but they are often accused of extreme subjective input when estimating the width of missing soft tissue.
"Here, we display an alternative loom where a minimum convex hull is derived exactly from the point cloud generated by laser-scanning mounted skeletons. This has the benefit of requiring minimal user interference and is therefore more objective and far quicker.
"We tested this method on 14 large-bodied mammalian skeletons and established that it consistently underestimate body mass by 21%. We suggest that this is a robust method of estimating body mass where a mounted skeletal reconstruction is available and show its usage to predict the body mass of one of the main, comparatively complete sauropod dinosaurs, Giraffatitan brancai, as 23,200 kg.
"The value we got for Giraffatitan is at the low range of preceding estimates; although it is still huge, some of the huge estimates of the past 80 tonnes in 1962 are overstated. Our method provides a much more accurate gauge and shows dinosaurs, while still huge, is not as big as earlier thought."