Abstract
Body mass reconstructions of extinct vertebrates are most robust when complete to near-complete skeletons allow the reconstruction of either physical or digital models. Digital models are most efficient in terms of time and cost, and provide the facility to infinitely modify model properties non-destructively, such that sensitivity analyses can be conducted to quantify the effect of the many unknown parameters involved in reconstructions of extinct animals. In this study we use laser scanning (LiDAR) and computer modelling methods to create a range of 3D mass models of five specimens of non-avian dinosaur; two near-complete specimens of Tyrannosaurus rex, the most complete specimens of Acrocanthosaurus atokensis and Strutiomimum sedens, and a near-complete skeleton of a sub-adult Edmontosaurus annectens. LiDAR scanning allows a full mounted skeleton to be imaged 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 lungs and air sacs can be reconstructed. This has allowed calculation of body segment masses, centres of mass and moments or inertia for each animal. However, any soft tissue reconstruction of an extinct taxon inevitably represents a best estimate model with an unknown level of accuracy. We have therefore conducted an extensive sensitivity analysis in which the volumes of body segments and respiratory organs were varied in an attempt to constrain the likely maximum plausible range of mass parameters for each animal. Our results provide wide ranges in actual mass and inertial values, emphasizing the high level of uncertainty inevitable in such reconstructions. However, our sensitivity analysis consistently places the centre of mass well below and in front of hip joint in each animal, regardless of the chosen combination of body and respiratory structure volumes. These results emphasize that future biomechanical assessments of extinct taxa should be preceded by a detailed investigation of the plausible range of mass properties, in which sensitivity analyses are used to identify a suite of possible values to be tested as inputs in analytical models.
Highlights
The mass properties of dinosaurs have been the subject of ongoing scientific investigation for over a century [1,2,3,4,5,6,7], reflecting their unique range of body forms and the fundamental importance of mass properties as morphological, physiological and ecological traits in biological organisms
In the slimmer models we reduced the diameter of the Non-Uniform Rational BSpline (NURBs) circles in the neck, thoraxic, sacral, tail and hind limb segments by 7.5%, while in the two larger models these segments were increased by 7.5% and 15% with respect to the best estimate models
Total body mass estimates of the four non-avian theropods range from 423 kg for Struthiomimus to 7655 kg for Tyrannosaurus rex BHI 3033
Summary
The mass properties of dinosaurs have been the subject of ongoing scientific investigation for over a century [1,2,3,4,5,6,7], reflecting their unique range of body forms and the fundamental importance of mass properties as morphological, physiological and ecological traits in biological organisms. Body size has featured prominently in attempts to explain temporal and spatial trends in fossil species duration [18,19,20], directional changes within lineages [21,22,23,24,25,26] and survivorship patterns during mass extinction events [27; but see 28]. Body mass is considered the single most important factor affecting locomotor mechanics and performance in terrestrial vertebrates [29,30,31,32,33,34,35]. Accurate quantitative predictions of mass properties are fundamental to biomechanical analyses of extinct organisms and to understanding patterns of diversification and extinction in the fossil record
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