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.

S1 Blender setup example for Alligator mississippiensisS2 Blender setup example for Buteo buteoS3 Blender setup example for Allosaurus fragilisS4 Blender setup example for Tyrannosaurus rexS5 Blender setup example for Erlikosaurus andrewsiS6 Muscle strain script for Alligator mississipiensisPython script for strain analysis for Alligator mississippiensis (.txt)S7 Muscle strain script for Buteo buteoPython script for strain analysis for Buteo buteo (.txt)S8 Muscle strain script for Allosaurus fragiliisPython script for strain analysis for Allosaurus fragilis (.txt)S9 Muscle strain script for Tyrannosaurus rexPython script for strain analysis for Tyrannosaurus rex (including comments) (.txt)S10 Muscle strain script for Erlikosaurus andrewsiS11 Data with strain factors for studied taxaS12 Movie showing gape cycles and strain factors with a muscle resting length at 3 degreesMovie showing gape cycles and strain factors with a muscle resting length at 3 degrees (.mov)S13 Movie showing gape cycles and strain factors with a muscle resting length at 6 degreesMovie showing gape cycles and strain factors with a muscle resting length at 6 degrees (.mov)