In order to make any estimates of how fast a prehistoric animal ran or how much it ate, in order to understand its metabolism, body mass is a necessary factor to take into account, explained palaeontologist Charlotte Brassey at the Natural History Museum of London. Until now, mass was approximated on the basis of thigh-bone and upper-arm-bone dimensions. But in order to check the accuracy of this method, professor Brassey and her team of researchers scanned all the bones that had been found from a female Stegosaurus stenops (nicknamed Sophie) – 360 bones in total, representing 80% of her skeleton – and measured the volume of their digitized images. By analogy with living animals, the volume of the whole body and then the mass of the dinosaur were calculated. The results of this research were published in Biology Letters.

The Stegosaurus is estimated to have weighed 3,527 pounds during its lifetime, which is a number very close to the one calculated by measuring thighs and upper-arms. However, this new method is more reliable and thus an important confirmation for the traditional one. Furthermore, professor Brassey’s method comes to correct the initial supposition of the old calculation technique, which had produced a figure for the Stegosaurus’s weight twice as big as the one discovered now. The error in that first calculation was due to the fact that scientists hadn’t taken into consideration Sophie’s still developing body (the dinosaur was not yet mature when she died), which would have accounted for the difference between bone-mass and body-mass (because the bones grow faster in adolescence, and the body mass accumulates later on). Having adjusted this detail, the two methods of calculating the mass of the Stegosaurus reached the same number.

Having completed this project, professor Brassey’s next aim is to add muscles to the digital projection of Sophie’s skeleton in order to reconstruct the Stegosaurus’s movement.

image source: BBC news