Evolution of Body Form, Posture, and Locomotion in Birds and Dinosaurs

The evolution of birds from non-avian dinosaurs is a long-standing interest in vertebrate palaeontology, which has been rigorously investigated over the past few decades, driven by methodological advances and the discovery of exciting new fossils. Innovations in body form, posture, and locomotion represent key ecomorphological changes across this transition. However, while particular emphasis has been placed on modifications to the forelimb and the origins of flight, studies focusing on hind limb evolution have been scarcer and primarily qualitative in nature. Locomotion is a whole-body task, and the hind limb may provide a wealth of information with which to test hypotheses about avian evolution, and assess the ecological context of the origins of flight. Indeed, in terms of gross anatomical changes, birds are unique in their use of a crouched hindlimb posture (unlike their more erect dinosaurian ancestors), a trait which might theoretically be predicted to incur performance penalties, by decreasing the efficiency of locomotion.
This project seeks to address these issues and construct a more holistic view of avian locomotory evolution, through investigation of the hypothesis that crouched hind limb posture evolved under selection for enhanced locomotor performance on branches, which deform under the animal's weight. To achieve this, experimental data will be collected from live birds walking and jumping on surfaces of varying compliance. This data will provide new insights into the biomechanics of crouched posture, and can be combined with anatomical information to validate computer models of avian locomotion. These models will be used to inform simulations of fossil taxa, allowing quantification of the performance impact of evolutionary changes to limb posture. By tracking the evolution of morphology and function, the role of the hind limb can be better integrated into broader ecomorphological theories of avian evolution. This will allow us to understand, for example, if the efficient use of crouched bipedalism preceded the evolution of powered flight, and therefore served as an exaptation through which stem birds could locomote effectively in an arboreal setting.

Numerous theories have been proposed as selective pressures behind the evolution of flight in birds. However, to-date none have provided a mechanistic link between changes in gross anatomy and body shape described by fossils and the biomechanics underpinning this major ecological shift. Here we propose a new hypothesis: that changes in body shape and posture were initially driven by selection for enhanced jumping and walking performance on compliant substrates (i.e. branches).

To investigate the correlation between gross anatomical changes and arboreal locomotor modes in birds by:

1. Collecting biomechanical data on birds jumping and walking on hard substrates and branches of varying compliance in a controlled laboratory setting.
2. Collecting biomechanical data on birds jumping and walking on hard substrates and branches of varying compliance in zoos using 3D videophotogrammetry and pressure sensors.
3. Using data from OBJ1 to validate a computer model of birds jumping and walking.
4. Use the validated computer simulation approach to model the impact of gross anatomical changes seen in bird-line fossils to quantify effects on biomechanical performance on walking and jumping on hard vs. compliant substrates.

This project is grounded in a new ecomorphological hypothesis for the evolution of arboreality and flight in birds. This is a contentious and intensely researched area and we expect that application of novel experiments and computer simulations to our new hypothesis will make a major impact. If supported, our hypothesis will be the first provide a holistic link between gross anatomical changes, biomechanics and major ecological shifts (i.e. the origin of flight) during early bird evolution.