Scientists are using laser imaging and three-dimensional computer modeling to investigate how fat – or fit – Tyrannosaurus rex (T. rex) and his fellow dinosaurs were. Karl Bates and his colleagues in the paleontology and biomechanics research group at the University of Manchester reconstructed the bodies of five dinosaurs, two T. rex (Stan at the Manchester Museum and the Museum of the Rockies cast MOR555), an Acrocanthosaurus atokensis, a Strutiomimum sedens and an Edmontosaurus annectens. The team found that the smaller Museum of the Rockies T. rex could have weighed anywhere between 5.5 and 7 tons, while Stan, the larger specimen, might have weighed as much as 8 tons.Photograph of one of the mounted skeletons of the five nonavian dinosaurs modeled, Tyrannosaurus rex BHI 3033 in lateral view. (Images copyright ©2009 Bates et al.)Acrocanthosaurus atokensis was a large predatory dinosaur that looked like T. rex but with large spines on its back, and it roamed the earth much earlier in the mid-Cretaceous period, around 110 million years ago. The team suggests that Acrocanthosaurus probably weighed in at a similar mass to MOR555 and other medium-size adult T. rex at about 6 tons. The Strutiomimum sedens, whose name means “ostrich mimic,” lived alongside T. rex in the late Cretaceous period and probably weighed about half a ton. The reconstruction of Edmontosaurus annectens, a plant-eating hadrosaur was based on a juvenile specimen, but still weighed in at between 0.8 to 0.95 tons. As adults, some hadrosaurs grew as big as T. rex, again living in the late Cretaceous period. “Our technique allows people to see and decide for themselves how fat or thin the dinosaurs might have been in life. You can see the skeleton with a belly. Anyone from a five-year-old to a professor can see it and say, ‘I think this reconstruction is too fat or too thin,’ ” Bates said. (A) The mounted skeletons were scanned from a variety of perspectives to provide full 3-D coverage and eliminate ‘shadows’ in the data set. (B) The segmented right-hand side of the skeleton was aligned with Maya's x axis and mirrored to produce complete symmetrical models (T. rex MOR 555 in oblique right craniolateral and dorsal views). (C) Body outlines were constructed using Non-Uniform Rational B-Spline (NURBS) circles, with a single NURBS used to define the body outline around each vertebrae in the body segments (neck, thorax, sacrum and tail). Closed body cavities surfaces then were generated by ‘lofting’ a continuous surface through consecutive NURBS circles to produce discrete body volumes for each segment (T. rex MOR 555 in right lateral and oblique right craniolateral views). The team used laser scanning (lidar) and computer modeling methods to create a range of 3-D models of the specimens, attempting to reconstruct their body sizes and shape as in life. The laser scanner images the full mounted skeleton, resulting in a detailed 3-D model in which each bone retains its spatial position and articulation. This provides a high-resolution skeletal framework around which the body cavity and internal organs such as stomach, lungs and air sacs can be reconstructed and has allowed calculation of body segment masses, centers of mass and moments of inertia for each animal – all the information that is needed to analyze body movements. Having created their “best guess” reconstruction of each animal, they varied the volumes of body segments and respiratory organs to find the maximum plausible range of mass for the animals. Even scientists cannot be sure exactly how fat or thin animals such as T. rex were in life, and the team was interested in exactly how broad the range of possible values were for body mass. The investigators believe that the lower weight estimates are most likely correct because there is no good reason for the dinosaurs to weigh more than they need to, as this would affect their speed, energy use and demands on the respiratory system. The team tested the accuracy of its dinosaur measurements by calculating the body mass of a living creature – an ostrich – and found the results to be correct. The scientists said they will use the results to further investigate the locomotion of dinosaurs, specifically how they ran.Best estimate reconstruction of Tyrannosaurus rex BHI 3033 in (A) right lateral, (B) dorsal, (C) cranial and (D) oblique right craniolateral views (not to scale). “This study will help us in our research on how dinosaurs ran in 3-D rather than 2-D, as in previous studies,” Bates said. “Reconstructing more dinosaurs in such detail will allow us to examine changes in body mass and particularly center of mass as they evolved. As we know, dinosaurs evolved into birds. As they did so, the center of mass moved forward and different walking styles evolved. Although the dinosaurs we have reconstructed are not very close relatives of the birds, we can nevertheless see a small forward movement in the position of the center of mass from Acrocanthosaurus atokensis to the T. rex, which lies closer to modern birds on the evolutionary lines,” he added. The team's findings were published Feb. 19 in the Public Library of Science journal PLoS ONE; it is available here.