Quantifying pterosaur launch

: biomechanical modelling of ornithocheiraean pterosaur locomotion

Abstract

Launch is the main constraint on size in modern flying animals. Extinct Mesozoic flying vertebrates, the pterosaurs, have reached sizes considered impossible for modern volant animals. Pterosaurs are hypothesised to have utilised either a bipedal or quadrupedal launch to become airborne, yet there is no consensus and neither of these launch hypotheses have been fully tested quantitatively. To compare the quadrupedal launch hypothesis with both variants of the bipedal launch hypothesis, burst and countermovement, I have performed quantitative biomechanical simulations using a model 5m wingspan ornithocheiraean pterosaur. Using Range of Motion mapping I determined the ability of the model to assume the poses associated with both launch hypotheses given different degrees of soft tissue derived ROM expansion and constraints. The quadrupedal launch poses were found to fit within the model ROM while the bipedal launch required 10 additional femoral adduction to be viable. A full 3D musculoskeletal ornithocheiraean model was created in OpenSim and the moment arms of the key forelimb and hindlimb muscles were determined. Using muscle architecture data from extant phylogenetic bracket species the moment generating capacity of each launch hypothesis was calculated. Both bipedal launches were found to produce significantly smaller total moments than the quadrupedal launch. Applying the calculated moments, the ground reaction force (GRF) produced by the model through each of the hypothesised launch motions was calculated. The GRF was then used to calculate the accelerating force and ballistic trajectory of the launch and compared against the required height for the ornithocheiraean model to complete a flight stroke. Most quadrupedal launch models were able to successfully launch while out of all the bipedal launch models only the most extreme bipedal burst model was successful. The results of this thesis therefore quantitatively support the quadrupedal launch hypothesis over a bipedal launch hypothesis for ornithocheiraean pterosaurs.

Date of Award	6 Dec 2022
Original language	English
Awarding Institution	University of Bristol
Supervisor	Emily J Rayfield (Supervisor), E Martin-Silverstone (Supervisor), Colin Palmer (Supervisor) & Michael J Benton (Supervisor)