Multi-functional foot use during running in the zebra-tailed lizard (Callisaurus draconoides)

Area of Science:

• Biomechanics
• Locomotion
• Animal Physiology

Background:

• Animals running on solid surfaces utilize limb elasticity for energy return.
• Locomotion mechanics on yielding natural terrains are less understood.
• The zebra-tailed lizard (Callisaurus draconoides) is a desert reptile with unique hind feet for rapid movement.

Purpose of the Study:

• To investigate how leg, foot, and substrate mechanics influence the running performance of the zebra-tailed lizard on different surfaces.
• To quantify the energetic costs and kinematic adaptations during locomotion on solid versus granular substrates.

Main Methods:

• High-speed video analysis to capture 3D running kinematics.
• Application of a strut-spring model for hind limb mechanics on solid surfaces.
• Utilizing penetration force and subsurface foot rotation models for granular surfaces.

Main Results:

• The lizard's center of mass oscillates like a spring-mass system on both solid and granular surfaces.
• Hind foot mechanics save significant work on solid ground (~40%), acting as a strut-spring.
• On granular surfaces, the hind foot paddles through a fluidized medium, with energy loss to the substrate matching center of mass energy reduction.

Conclusions:

• The zebra-tailed lizard exhibits distinct locomotor strategies for solid and granular terrains.
• Hind limb and foot adaptations are crucial for efficient running across diverse substrates.
• Increased muscular work in the upper hind leg is required on granular surfaces to overcome energy losses.