Gigantic, but still lighter than expected: Brachiosaurs Image: Axel Mauruszat, Museum of Natural History Berlin
How much weight an extinct animal species once weighed is one of the things that most interest paleontologists in animal fossils. To find this out, they have two standard methods at their disposal: either the researchers create a model of the carcass and calculate its mass by means of its density. Alternatively, they can estimate the weight of an extinct animal using an equation based on the relationship between skeletal dimensions and the weight of today's species. Both methods, however, have their pitfalls, because the first is extremely time-consuming and the second very inaccurate. The better the chances for a new method, which presented scientists of the University of Manchester now, to establish itself as a standard for determining the weight of extinct animals: The researchers tested how accurately the weight of animals can be estimated if the corresponding skeletons with a Laser scanned. They used the skeletons of 14 large mammal species living today, such as polar bears, giraffes and elephants. Using the data from the scanning, the scientists reconstructed a three-dimensional model skeleton. They then calculated the minimum volume needed to cover the skeleton. Lastly, they estimated the weight of the animals by basing their density on horses. Compared to the actual average weight of each species, the results of the estimation proved surprisingly robust. "We tested the method on 14 large mammalian skeletons and showed that body weight is constantly underestimated by 21 percent, " says lead author William Sellers. The authors explain this result in such a way that the extra volume compared to the minimum consists mainly of muscle tissue. And the total muscle weight is usually proportional to the total weight of the body. Laser beams can help to estimate the weight of animals with astonishing precision on the basis of their skeletons: Picture above: Original skeleton of a polar bear; Middle: image obtained by laser scanning; below: Minimal wrap around the skeleton. The minimal body sheath weight was exactly 21 percent too low for all mammalian species tested. Image: Sellers et al., Biology Letters (2012) One of the most interesting findings was the application of the new method to the skeleton of a brachiosaurus (Giraffatitan brancai): According to earlier estimates, the giant had weighed up to 80 tons. The study from Manchester now suggests that this value was probably many times too high: The new method measured the weight of Brachiosauriers to just 23 tons. "Our method provides a much more accurate assessment and shows that dinosaurs, while quite powerful, were not quite as heavy as previously thought, " Sellers judges the study's findings. Accurate weight estimation of the laser-based method is made possible by using all available skeletal information, the researchers write. In addition, they require relatively little time and provide robust data. Although there is one drawback: one needs a reconstruction of the entire skeleton, for which a single bone find is not sufficient. Nevertheless, the researchers are convinced that the new method is currently the best way to estimate the weight of extinct animals.

William I. Sellers (University of Manchester) et al .: Biology Letters doi: 10.1098 / rsbl.2012.0263 © science.de - Maren Emmerich

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