What started as routine fossil cleaning turned into a major scientific surprise when researchers uncovered a tiny claw in a 500-million-year-old specimen where no claw should exist. That detail revealed Megachelicerax cousteaui, the oldest known relative of spiders, pushing the origins of this group back by 20 million years. The fossil shows that key features of modern spiders and horseshoe crabs were already emerging during the Cambrian Explosion.