Enrolled trilobites are fossilized specimens that show these ancient arthropods curled into tight, ball-like shapes. This behavior is similar to how modern pill bugs roll up for protection. Trilobites could fold their bodies by flexing their articulated segments, wrapping their head and tail shields together. This maneuver helped shield their soft undersides from predators and environmental dangers.

Enrollment was more than just a quirk. For trilobites, it was a life-saving adaptation that showcases their complexity as early arthropods.