Full-body biomechanical model and novel forelimb muscle forces in Tyrannosaurus rex

Abstract

Background: Tyrannosaurus rex is a popularly studied non-avian dinosaur with hundreds of papers investigating different aspects of its biology. The biomechanics of T. rex is of particular interest, with many analyses examining its locomotion and feeding. However, biomechanical models often focus on only one region of the body rather than incorporating multiple and some muscle groups have never been previously reconstructed in this taxon. Here we present (1) a new full-body model of Tyrannosaurus musculature, and (2) muscle force estimates for forelimb protractors and retractors, which have never yet been biomechanically analyzed. Methods: We created this model by generating a 3D render of a Tyrannosaurus rex’s skeleton with photogrammetry and sculpting the musculature onto the skeleton. The lengths and volumes of these scaled muscle models were then measured to calculate their physiological cross-sectional areas and ultimately estimate the maximum contractile force of each muscle for three possible fiber lengths. Results: The largest of the humeral protractors, the m. pectoralis, was estimated to have a maximum contractile force of 3,860 N – 11,000 N, while the largest humeral retractor, the m. latissimus dorsi, was estimated to have a maximum contractile force of 3,770 N – 10,800 N. Discussion: These forces will inform future calculations to explore how T. rex could use different muscle groups in its movements in addition to developing a better understanding of its forelimb biomechanics, which are largely undescribed. Furthermore, these muscle models will be presented as a digital atlas of T. rex’s skeletal muscle morphology.