Anomalocaris

Early-Middle Cambrian. The earliest trilobites wore spiked armor, because there was danger overhead: Predatory Anomalocaris swimming above the Cambrian sea bottom. Anomalocaris grew up to be up to a yard long. It was bigger and stronger than any early trilobite. Swimming legs worked like propellers that drove the predator through the water, making it one of the speediest animals in the Cambrian ocean.