Fibular reduction and the evolution of theropod locomotion

Area of Science:

• Paleontology
• Biomechanics
• Evolutionary Biology

Background:

• The avian fibula's reduction during dinosaur evolution was historically considered biomechanically insignificant.
• Previous research focused on the fibula's morphology without fully exploring its functional implications.

Purpose of the Study:

• To investigate the functional role of the reduced avian fibula in locomotion.
• To challenge the assumption that fibular reduction had minimal biomechanical consequences.

Main Methods:

• Comparative three-dimensional kinematic analyses of avian locomotion.
• Examination of transitional fossil morphologies to reconstruct evolutionary changes.

Main Results:

• The reduced fibula is essential for enabling extreme knee long-axis rotation (LAR).
• Fibular reduction facilitated a shift from hinge-like knee motion in early theropods to complex 3D limb control in modern birds.
• A mid-shank articulation in early theropods restricted knee motion, with subsequent fibular freeing enabling LAR.

Conclusions:

• Fibular reduction was a critical evolutionary step, not a passive byproduct.
• The evolution of extreme LAR, enabled by fibular reduction, fundamentally reshaped theropod locomotor capabilities.
• This study highlights the significant biomechanical impact of skeletal modifications in vertebrate evolution.