SUSTAINED MESOZOIC-CENOZOIC DIVERSIFICATION OF MARINE METAZOA: A ROBUST SIGNAL FROM THE FOSSIL RECORD

Paleontological data provide a key historical record of biodiversity dynamics, but their interpretation is controversial due to geological and sampling biases. Numerous compilations of raw data suggest that marine metazoans diversified dramatically during the late Mesozoic and Cenozoic, with genus richness rising to about 2-4 times Paleozoic levels. However, bias-corrected analyses have indicated much less Cenozoic diversification, with most published curves showing leveling off or decreasing diversity in the Neogene, and these analyses are cited as evidence that biases strongly conceal underlying biological patterns in the global fossil record. We applied the SQS method to the Paleobiology Database (PBDB, paleobiodb.org) to re-examine these biases. Variation in data quantity did affect observed diversity, as in any study of taxonomic richness. However, taphonomic heterogeneity had only minor effects on the diversity curve once overall sampling intensity was standardized, indicating that preservation affects observed global diversity primarily through its effects on sample size. After correcting for biases, genus richness still increased substantially and continuously from the Jurassic to the Neogene. In the Cenozoic, observed richness rose to twice the Paleozoic average, which is within the range of outcomes seen in analyses of raw data, suggesting that the global marine fossil record does preserve first-order signals of diversity history. Previous standardized analyses did not capture this diversification in full because they were based on incomplete data that excluded some marine metazoans. Further improvements to the curve are expected as more data are added to the PBDB (particularly from undersampled clades and geographic regions) and as existing data are vetted, but consilience among methods suggests that the first-order signal of long-term diversification is robust. The Mesozoic-Cenozoic Radiation is one of the key features of marine animal diversity history—not since the early Paleozoic had diversity changed substantially and permanently.