51% of all marine families, 82% of all genera, an estimated 93-97% of all species.
Having survived 2 mass extinctions, only a few localised and specialised populations of trilobites remained. These prehistoric relatives of crabs, spiders and insects finally disappeared from the fossil record completely, bringing to an end 270 million years of trilobites roaming the oceans.
The scorpion-like eurypterids, formidable marine predators that thrived in warm shallow water, were another major group that ceased to exist. And the extinction of reef-building corals meant an entire ecosystem vanished.