Meeting Abstract
The archosaurs are a clade of reptiles that underwent repeated evolutionary acquisition of bipedality throughout their 250 million year history, including the most speciose lineage of bipeds, the birds. Studies of avian locomotion can therefore illuminate locomotor evolution in archosaurs, and the biomechanics of striding bipedalism in general. We collected synchronised marker-based XROMM (biplanar high speed X-ray video) and ground reaction force data to investigate locomotion in Eudromia elegans across a range of walking and running speeds. As palaeognaths, tinamous complement previous studies of other avian species, and can help assess the ancestral state for hindlimb form and function in crown-group birds. Our data show that tinamou use hindlimb kinematics that are largely comparable to those recorded in other species (e.g., guineafowl, ostrich), although some differences do exist, such as markedly greater long-axis rotation of the tibiotarsus. In order to better understand the underlying musculoskeletal mechanisms that control limb movement, we also synthesised our experimental data with a three-dimensional musculoskeletal model of the tinamou hindlimb. The model was based on anatomical dissections, iodine-contrasted micro-tomographic scans and measured segment inertial properties, and includes all the major muscles of the hindlimb. Feeding the experimentally recorded data into the model, we used inverse dynamics to estimate external joint moments, and static optimization to estimate muscle activation patterns during the stride cycle. Our preliminary simulations produced activation patterns consistent with experimental electromyography data, lending confidence to the use of these models for extinct archosaurian bipeds. Further simulation using dynamic optimization approaches will allow us to explore the importance of tendon stretch and recoil in birds during locomotion.
