Reefal regions were biodiversity hotspots throughout the Phanerozoic.

Reefs are important hotspots of marine biodiversity today and have acted as cradles of diversification in the geological past. However, we know little about how the diversity of reef-supporting regions varied through deep time, and how this differed from other regions. We quantified regional diversity patterns in reef-supporting and non-reef-supporting regions in the fossil record of Phanerozoic marine invertebrates. Diversity in reef-supporting regions is on average two- to threefold higher than in non-reef-supporting regions and has been remarkably stable over timescales of tens to hundreds of millions of years. This signal is present in both reefal and non-reefal facies within reef-supporting regions, suggesting that reefs enriched diversity in surrounding environments. Sepkoski's "Modern Fauna," an assemblage of higher taxa that includes gastropods, bivalves, and echinoids, has been a key component of reef-supporting regions since the Paleozoic, contrasting with its later rise to dominance in non-reef-supporting regions during the later Mesozoic-Cenozoic.