Flapping before Flight: High Resolution, Three-Dimensional Skeletal Kinematics of Wings and Legs during Avian...

Area of Science:

• Paleontology
• Evolutionary Biology
• Biomechanics

Background:

• Avian flight represents a significant evolutionary achievement in vertebrates.
• Juvenile birds and early theropods possess rudimentary flight apparatuses, differing from adult birds.
• Skeletal and feather functions in flight origins are debated, with limited understanding of skeletal kinematics.

Purpose of the Study:

• To investigate the developmental trajectory of the avian flight apparatus.
• To correlate skeletal kinematics, aerodynamic performance, and locomotor transitions in developing birds.
• To challenge existing notions on the function of early wings and theropod flight capabilities.

Main Methods:

• Utilized X-ray Reconstruction of Moving Morphology (XROMM) to visualize skeletal movement in developing chukars (Alectoris chukar).
• Analyzed ontogenetic changes in skeletal kinematics and aerodynamic performance.
• Examined the transition from pre-flight flapping behaviors to full flight capacity.

Main Results:

• Developing chukars exhibit an "avian" flight stroke early in ontogeny.
• Wings and legs are used cooperatively in early flapping behaviors.
• Increased aerodynamic output is counteracted by greater skeletal "channelization" as flight capacity develops.

Conclusions:

• The initial function of developing wings in birds is to enhance leg performance.
• Flapping wings may be viewed as adaptations or exaptations for improving leg function.
• Findings challenge the traditional view of flight origins, emphasizing the role of wings in augmenting terrestrial locomotion.