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, 2 (11), 150495
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Estimating Cranial Musculoskeletal Constraints in Theropod Dinosaurs

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Estimating Cranial Musculoskeletal Constraints in Theropod Dinosaurs

Stephan Lautenschlager. R Soc Open Sci.

Abstract

Many inferences on the biology, behaviour and ecology of extinct vertebrates are based on the reconstruction of the musculature and rely considerably on its accuracy. Although the advent of digital reconstruction techniques has facilitated the creation and testing of musculoskeletal hypotheses in recent years, muscle strain capabilities have rarely been considered. Here, a digital modelling approach using the freely available visualization and animation software Blender is applied to estimate cranial muscle length changes and optimal and maximal possible gape in different theropod dinosaurs. Models of living archosaur taxa (Alligator mississippiensis, Buteo buteo) were used in an extant phylogenetically bracketed framework to validate the method. Results of this study demonstrate that Tyrannosaurus rex, Allosaurus fragilis and Erlikosaurus andrewsi show distinct differences in the recruitment of the jaw adductor musculature and resulting gape, confirming previous dietary and ecological assumptions. While the carnivorous taxa T. rex and Allo. fragilis were capable of a wide gape and sustained muscle force, the herbivorous therizinosaurian E. andrewsi was constrained to small gape angles.

Keywords: Dinosauria; digital reconstruction; functional morphology; muscle strain; musculature.

Figures

Figure 1.
Figure 1.
Digital models of the studied fossil theropod and extant archosaur taxa in a simplified phylogenetic context. Cranial models not to scale.
Figure 2.
Figure 2.
Model and analysis set-up in Blender exemplified for Tyrannosaurus rex shown in (a) solid and (b) wireframe view.
Figure 3.
Figure 3.
Muscle strain factors plotted against gape angle for (a,c,e) Alligator mississippiensis and (b,d,e) Buteo buteo. Analysis were run with resting length set at a gape angle of (a,b) 3.0°, (c,d) 6.0° and (e,f) 9.0°. Muscle abbreviations as in table 1.
Figure 4.
Figure 4.
Gape angles at optimal and maximum tension limit for Alligator mississippiensis with muscle resting lengths at a gape angle of (a) 3.0°, (b) 6.0° and (c) 9.0°. Bar diagrams show strain factors of individual muscles at optimal and maximum tension limit. Muscle abbreviations as in table 1.
Figure 5.
Figure 5.
Gape angles at optimal and maximum tension limit for Buteo buteo with muscle resting lengths at a gape angle of (a) 3.0°, (b) 6.0° and (c) 9.0°. Bar diagrams show strain factors of individual muscles at optimal and maximum tension limit. Muscle abbreviations as in table 1.
Figure 6.
Figure 6.
Muscle strain factors plotted against gape angle for (a,b) Allosaurus fragilis, (c,d) Tyrannosaurus rex and (e,f) Erlikosaurus andrewsi. Analysis were run with resting length set at a gape angle of (a,c,e) 3.0° and (b,d,f) 6.0°. Muscle abbreviations as in table 1.
Figure 7.
Figure 7.
Gape angles at optimal and maximum tension limit for (a) Allosaurus fragilis, (b) Tyrannosaurus rex and (c) Erlikosaurus andrewsi with muscle resting length at a gape angle of 3.0°. Bar diagrams show strain factors of individual muscles at optimal and maximum tension limit. Muscle abbreviations as in table 1.
Figure 8.
Figure 8.
Gape angles at optimal and maximum tension limit for (a) Allosaurus fragilis, (b) Tyrannosaurus rex and (c) Erlikosaurus andrewsiwith muscle resting length at a gape angle of 6.0°. Bar diagrams show strain factors of individual muscles at optimal and maximum tension limit. Muscle abbreviations as in table 1.

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