February 24, 2009--Scientists in the paleontology and biomechanics research group at the University of Manchester (Manchester, UK) have reconstructed the bodies of five dinosaurs using light detection and ranging (LiDAR) and computer modeling methods. The work has helped the researchers determine the dinosaurs' real-life body sizes and shapes by calculating body segment masses, centers of mass, and moments of inertia for each animal. It has also given a view into the animals' body movements.
Karl Bates and his colleagues, whose findings are published in PLoS ONE, have reconstructed the bodies of two Tyrannosaurus rex, an Acrocanthosaurus atokensis, a Strutiomimum sedens and an Edmontosaurus annectens. They created a range of 3D 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 3D 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. This has allowed calculation of body segment masses, centers of mass and moments of inertia for each animal--all the information needed to analyze body movements.
Having created their 'best-guess' reconstruction of each animal, they then 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 like T. rex were in life, and the team was interested in exactly how broad the range of possible values were for body mass. They believe that the lower weight estimates are most likely to be correct as 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 also measured the body mass of an ostrich, as an existing subject that would show how accurate their technique was, and found the results to be correct.
The team found that the smaller T. rex weighed between 5.5 and 7 tons, while the larger specimen might have weighed as much as 8 tons. The team suggests that the Acrocanthosaurus atokensis, a large predator that looked like T. rex, had spines on its back weighed in at about 6 tons. The Strutiomimum sedens, whose name means "ostrich mimic," weighed between 0.4 and 0.6 tons. 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.
"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,'" said Bates.
The team will now use the results to further investigate the locomotion of dinosaurs, specifically how they ran."This study will help us in our research on how dinosaurs ran in 3-D rather than 2-D as in previous studies," Bates explained.
Bates added that reconstructing more dinosaurs in such detail will enable understanding of body mass and particularly center of mass as they evolved. "As we know, dinosaurs evolved into birds," he said. "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 forwards movement in the position of the centre of mass from Acrocanthosaurus atokensis [which lived in the mid Cretaceous period] to the T. rex [which lived later, in the late Cretaceous period], which lies closer to modern birds on the evolutionary lines."
For more information, see the paper, Estimating Mass Properties of Dinosaurs Using Laser Imaging and 3D Computer Modelling, in PLoS ONE.
Posted by Barbara G. Goode, barbarag@pennwell.com, for Laser Focus World.
