The evolutionary recovery of planktic foraminifera from the Cretaceous-Paleogene mass extinction was closely linked to recovery of the marine carbon system. Both the evolutionary recovery and the biogeochemical recovery occurred in two stages. The second stage of evolutionary radiation peaked nearly four million years after the extinction, immediately after the abrupt final recovery of the organic flux to deep waters. The timing of these events suggests that the final postextinction recovery of planktic foraminiferal diversity was directly contingent on the final recovery of the marine carbon cycle. This second radiation was defined by the diversification of tropical photosymbiotic forms that dominated low- and mid-latitude assemblages long into the Eocene. We hypothesize that this diversification was a result of the reappearance of oligotrophic oceans as the organic flux from the surface ocean to deep water fully recovered from the mass extinction.

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