Theropod locomotion and the impact of elastic structures in the axial skeleton

Abstract

Locomotor ability is a key factor controlling the capacity for animals to find food and/or flee danger and is often critical to survival. Theropod dinosaurs evolved a variety of locomotor abilities that were controlled by a relatively conservative bauplan, but diverse body size. Extensive work has been previously undertaken on the evolution and function of the caudofemoral musculature, as these were the main hind limb retractors in large theropods, but not accounting for the impact of the cube-square law, other than in relation to muscle mass. Locomotor ability has been previously constrained by estimating values for muscle mass, as the energetic cost of locomotion scales with body mass. However, as body mass increases, it has been suggested that tendinous elastic structures make an increasingly significant contribution to locomotor ability, given linear dimensions of an organism increase, its volume cubes (cube-square law), placing increasing energy demands on proportionally less muscle mass. This study identifies structures in the vertebral column of a tyrannosaur, Gorgosaurus, which potentially contributes to elastic recoil during locomotion and therefore helps reduce energetic cost. This suggests that the storage of elastic energy, as identified through osteological correlates, aids theropod locomotion, resulting in significant energy savings during locomotion. This study identifies vertebral morphology that can provide supporting evidence for the existence and location of attachment sites of elastic structures that during locomotion coupled with natural gait frequency, resulting in an optimised musculoskeletal system. The vertebral morphology of the axial skeleton of Gorgosaurus supports the presence of an elastic recoil system and indicates the importance of elastic structures in theropod locomotion. Through morphological analysis of vertebrae, using Principle Component Analysis (PCA), it was possible to identify and constrain Vertebral Functional Units (a new term used in this study) that function as proxies (osteological correlates) for elastic storage structures. This study also compared vertebral osteological correlate PCA results for other theropod dinosaurs (data from Pittman et al., 2013), finding similarities between Gorgosaurus and the larger tyrannosaur Tyrannosaurus rex. The implication for larger theropods, such as T. rex, are clear, given elastic structures appear to play a more important role in locomotor ability with increasing size. If such structures are not accounted for when building computer models and locomotor simulations, it is possible that the optimal locomotor ability of large theropods is being significantly underestimated. The integration of elastic trunk recoil to computer models could lead to a revaluation in the cursorial behaviour and the running ability of theropods and has implications for predatory dinosaur ecology and associated modes of life.

Date of Award	27 Jun 2024
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Phillip Manning (Main Supervisor) & William Sellers (Co Supervisor)