Cretaceous foraminifera and the evolutionary history of planktic photosymbiosis

Ecotypic correlations between stable isotopic signals and skeletal size ind icate that some Late Cretaceous serial planktic foraminifera were strongly photosymbiotic. In contrast, coeval trochospiral planktic foraminifera do n ot exhibit the isotope/size signatures that typify strongly photosymbiotic species. Comparison to Cenozoic taxa demonstrates that photosymbiosis has r ecurred throughout planktic foraminiferal history and has evolved independe ntly in superfamilies characterized by very different gross skeletal morpho logies. The historical contingency of that evolution is illustrated by the consequences of the Cretaceous/Paleogene mass extinction, which terminated the Cretaceous lineages of photosymbiotic planktic foraminifera but did not permanently extinguish photosymbiont reliance by planktic foraminifera.