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, 4 (2), e4532

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

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

Karl T Bates et al. PLoS One.

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.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. Photographs of the mounted skeletons of the five non-avian dinosaurs modelled.
(A) Tyrannosaurus rex BHI 3033 in lateral view, and (B) Acrocanthosaurus atokensis NCSM 14345, Tyrannosaurus rex MOR 555, Edmontosaurus annectens BHI 126950 and Struthiomimus sedens BHI 1266 (top left to bottom right).
Figure 2
Figure 2. LiDAR data collection and processing.
(A) The mounted skeletons were scanned from a variety of perspectives to provide full 3D 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 were then 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).
Figure 3
Figure 3. Best estimate reconstructions of thoracic and pharyngeal air sacs in Tyrannosaurus rex MOR 555, shown in oblique right craniolateral views.
Figure 4
Figure 4. Volumetric model of an extant ostrich (Struthio camelus) based on a specimen (BB.3462) mounted at the Manchester Museum (UK), shown in (A) right lateral, (B) oblique right craniolateral, (C) cranial and (D–E) dorsal views (E with hind limb segments removed).
Figure 5
Figure 5. 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).
Figure 6
Figure 6. Best estimate reconstruction of Tyrannosaurus rex BHI MOR 555 in (A) right lateral, (B) dorsal, (C) cranial and (D) oblique right craniolateral views (not to scale).
Figure 7
Figure 7. Best estimate reconstruction of Acrocanthosaurus atokensis NCSM 14345 in (A) right lateral, (B) dorsal, (C) cranial and (D) oblique right craniolateral views (not to scale).
Figure 8
Figure 8. Best estimate reconstruction of Struthiomimus sedens BHI 1266 in (A) right lateral, (B) dorsal, (C) cranial and (D) oblique right craniolateral views (not to scale).
Figure 9
Figure 9. Best estimate reconstruction of Edmontosaurus annectens BHI 126950 in (A) right lateral, (B) dorsal, (C) cranial and (D) oblique right craniolateral views (not to scale).
Figure 10
Figure 10. The three alternative models of Tyrannosaurus rex BHI 3033 in lateral, oblique right craniolateral and dorsal views.
Neck, thoracic, sacral, tail and proximal hind limb segments have been increased by (A) 15% and (B) 7.5% in the two larger models, and (c) decreased by 7.5% in the smaller model.
Figure 11
Figure 11. The three alternative models of Tyrannosaurus rex MOR 555 in lateral, oblique right craniolateral and dorsal views.
Neck, thoracic, sacral, tail and proximal hind limb segments have been increased by (A) 15% and (B) 7.5% in the two larger models, and (c) decreased by 7.5% in the smaller model.
Figure 12
Figure 12. The three alternative models of Acrocanthosaurus atokensis NCSM 14345 in lateral, oblique right craniolateral and dorsal views.
Neck, thoracic, sacral, tail and proximal hind limb segments have been increased by (A) 15% and (B) 7.5% in the two larger models, and (c) decreased by 7.5% in the smaller model.
Figure 13
Figure 13. The three alternative models of Struthiomimus sedens BHI 1266 in lateral, oblique right craniolateral and dorsal views.
Neck, thoracic, sacral, tail and proximal hind limb segments have been increased by (A) 15% and (B) 7.5% in the two larger models, and (c) decreased by 7.5% in the smaller model.
Figure 14
Figure 14. The three alternative models of Edmontosaurus annectens BHI 126950 in lateral, oblique right craniolateral and dorsal views.
Neck, thoracic, sacral, tail and proximal hind limb segments have been increased by (A) 15% and (B) 7.5% in the two larger models, and (c) decreased by 7.5% in the smaller model.
Figure 15
Figure 15. HAT (left) and whole body (right) centres of mass for each model of (A) Tyrannosaurus rex BHI 3033, (B) Tyrannosaurus rex MOR 555, (C) Acrocanthosaurus atokensis NCSM 14345, (D) Struthiomimus sedens BHI 1266 and (E) Edmontosaurus annectens BHI 126950 (not to scale).

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