In order to protect themselves from predators, Phacops rana would roll into a ball with its hard exoskeleton on the outside as protection. Many other trilobites possessed the same ability, but Phacops rana nearly perfected it. The slightest amount of sediment would trigger their senses, and Phacops rana would be hidden in a tiny shelter made of its own body. Although this safety feature often helped them to evade predators, occasionally it backfired and the trilobite would be buried under heavy sediment. Their fossils can still be found in balled-up positions 400 million years later.
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