Estimating Mass Properties of Dinosaurs Using Laser Imaging and 3D Computer Modelling

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.

The Tail of Tyrannosaurus: Reassessing the Size and Locomotive Importance of the M. caudofemoralis in Non‐Avian Theropods

“…The current prevalent fashion among paleoartists is to depict the tails of most dinosaurs, but particularly theropods, as relatively unmuscular and laterally compressed. This is true not only of depictions made strictly for aesthetic purposes but also of those intended to support scientific research, such as estimations of mass (for example, Paul, 1997;Bates et al, 2009). The less-than-robust tail depictions are consistent with the more traditional tail muscle restoration technique described.…”

“…Based on mass estimates of other Gorgosaurus specimens (Paul, 1988), the body mass of TMP 1991.36.500 can be estimated as roughly 400 kg, and the mass of BHI 3033 has been estimated as in the range of 3,800-4,500 kg (Stevens et al, 2008; but see Bates et al, 2009 for an alternative interpretation). The need for relatively larger locomotive muscles in absolutely larger taxa has been well established (Biewener, 1989;Roberts, 1998).…”

Minimum convex hull mass estimations of complete mounted skeletons

“…Such a relationship between convex hull volume and body mass has the advantage of being potentially robust when used for extrapolating body masses for very large vertebrates. The major advantage of volumetric reconstructions in general is that they use the maximum information from the complete skeleton [1] and therefore avoid the single bone problem, where a species or an individual has limbs of unusual size that can lead to large errors. However, volumetric reconstructions are not without difficulties.…”

“…Therefore, there has been considerable demand for accurate techniques to reliably estimate body mass from skeletal remains for over a century [3]. There are two standard approaches: the volumetric approach, where a model of the animal is produced and its body mass calculated from its density; and the predictive regression approach, where a relationship between linear dimensions and body mass is generated from empirical data (see [1] for review). Volumetric approaches have the advantage of maximizing the information content of the complete skeleton, but they have the disadvantage that they require considerable time-consuming user input to generate the body outline.…”

Subject-specific body segment parameter estimation using 3D photogrammetry with multiple cameras

“…Thus, using segment and population specific densities (and scaling factors) may improve the accuracy of the presented methodology if such values are available or derived. Similarly important contributions to segmental mass distribution such as the presence of the lungs within the torso can be modelled explicitly which may lead to small but important shifts in the centre of mass (Bates et al, 2009). …”