Though less famous than the Cambrian explosion, the Ordovician featured an adaptive radiation, which was no less remarkable. Marine genera increased fourfold, resulting in 12% of all known Phanerozoic marine fauna. Another change in the fauna was the strong increase in filter feeding organisms. The articulate brachiopods, cephalopods, and crinoids took over. Articulate brachiopods, in particular, largely replaced trilobites in shelf communities. This illustrates the greatly increased biodiversity of carbonate shell-secreting organisms in the Ordovician compared to the Cambrian. Although solitary corals date back to at least the Cambrian, reef-forming corals appeared in the early Ordovician.