Paleobiological data provide a key historical record of global biodiversity dynamics, but their interpretation is controversial due to geological and sampling biases. Raw data suggest that marine metazoans diversified dramatically during the late Mesozoic and Cenozoic, whereas bias-corrected analyses based on occurrence-level data in the Paleobiology Database (PBDB) have indicated much less Cenozoic diversification. These standardized analyses are cited as evidence that biases strongly conceal underlying patterns in the global fossil record. However, we show that marine diversity did increase substantially and continuously from the Jurassic to the Neogene, even after correcting for biases in PBDB data. Previous standardized analyses did not capture this diversification in full because they were based on incomplete data. In the Cenozoic, observed richness rose to twice the Paleozoic average, which is within the range of values seen in analyses of raw data, suggesting that even the raw global marine fossil record preserves first-order signals of diversity history.