Leite, João Vasco; (2021) Evolutionary Biomechanics of the Dinosaur Hand. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The hand, or manus, is one of the most adaptable skeletal structures in tetrapods. Dinosaurs provide an excellent opportunity to study manus evolution due to their wide range of body sizes, locomotor stances, ecological niches, and behaviours. However, to date, our knowledge of the dinosaur manus has been based largely on straightforward anatomical descriptions and qualitative inferences of function, usually in the absence of a rigorous comparative framework. In this thesis, I present the first attempt to apply a series of quantitative, statistically robust and phylogenetically informed methods to the manus morphology of extinct Mesozoic dinosaurs, with an emphasis on non-avian species, sampling across their full taxonomic, temporal, functional and ecological spectrum. An assessment of manus configurations revealed unique evolutionary trajectories for each main lineage, but also convergence influenced by substantial ecological shifts. For the metacarpus of non-avian dinosaurs, positive allometry was the most prevalent scaling trend with body size, and the main shape variation factor was the degree of slenderness or stockiness. This pattern of shape variation also reflected two distinct strategies for weight-support in quadrupedal dinosaurs. However, other macroevolutionary patterns were shared across disparate clades, regardless of stance or diet. Indeed, the lack of functional and biomechanical constraints acting upon vestigial manüs and/or digits might have been responsible for greater deviations in morphology than strongly contrasting functions in fully-developed hands, such as grasping and locomotion. Lastly, three-dimensional modelling of range of motion in the early-diverging iguanodontian Camptosaurus provided further evidence that the manus in this taxon was adapted primarily for quadrupedal locomotion, with different functional contributions identified for each digit. This thesis represents a significant advancement in our understanding of the function and evolution of the dinosaur manus, grounded on novel quantitative approaches and an unmatched taxonomic scope. It adds an in-depth exploration of hypotheses relating to functional and biomechanical evolution, which are of relevance not only to dinosaurs but to tetrapods in general.

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