Mud to muscles: Dinosaur-bird locomotor evolution from fossil footprints

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Fossil footprints are a direct record of motion in a way that skeletons can never be. I will use fossil footprints to explore the locomotor changes that took place as birds evolved from theropod dinosaurs. Compared to their dinosaur ancestors, birds have a much-reduced tail and associated musculature. Did birds "give up" terrestrial locomotor superiority in order to fly? Are evolutionary changes in limb motions recorded in the fossil footprint record? If so, do they show a gradual change from tail-driven theropods to knee-driven birds, or do limb motions change abruptly with the appearance of specific traits?From mud to muscles, I will combine advanced 3D imaging, physical experimentation, and computer simulation to bridge the existing gap between fossil footprints and fossil skeletons, shedding light on this important evolutionary transition. Lab-based footprint-making experiments will combine kinematic and kinetic analyses to build an unprecedented view of footprint formation. Limb motions of long-extinct dinosaurs will be reconstructed using fossil tracks, then supercomputer simulations modelling every grain of a sediment responding to the indenting foot will be used to test the reconstructed motions. These simulations will compute the forces occurring between foot and ground. These forces and motions will drive musculoskeletal biomechanical simulations that will shed light, not only on what the feet of dinosaurs were doing, but on how the whole limbs and even bodies of these enigmatic animals once moved.By sampling fossil tracks from around the world, spanning the 230 million years since theropods first appeared, this project will recover fossilised motions along the dinosaur-bird lineage. Using rigorous, innovative methods, my proposal will unlock quantitative analysis of the way extinct animals moved, facilitating direct comparison with their extant descendants, and providing a unique view of locomotor evolution that cannot be recovered from bones alone.