Jackrabbit

Ears serve as thermal windows: 20% of body surface area, 40 blood vessels per cm², temperature 10°F warmer than ambient. Can dissipate up to 100% of metabolic heat through ears alone. In 100°F desert heat, pumps blood to ears for cooling. In 40°F desert night, restricts ear blood flow to conserve heat. Same structure, opposite functions, controlled by blood flow.