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Why do fast-running vertebrates have long lower legs and reduced toes?
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Locomotion
These birds largely reside in coastal areas of North America, although some populations live in the continent's interior along large rivers.
Fast-running, or cursorial, vertebrates have evolved elongated lower legs and reduced toes to maximize speed by optimizing the mechanics of limb movement.12
The primary reasons for these adaptations include:
- Pendulum Mechanics: A leg functions similarly to a pendulum. By reducing the weight at the end of the limbāspecifically by reducing the number of toes and concentrating muscles high on the upper legāthe animal decreases the limb's inertia. This allows for a faster oscillation speed and a quicker retractive-protractive cycle.31
- Efficiency and Speed: Lengthening the lower parts of the leg increases the distance covered per stride. Because heavy muscle mass is not concentrated near the tip of the limb, the animal can move its legs more rapidly without the restrictive effects of inertia.3
- Structural Specialization: The reduction and fusion of toes, such as the formation of cannon bones in many artiodactyls, provide a stable, lightweight structure that supports the animal while minimizing the energy required for rapid movement.32