Fern spore viability considered in relation to the duration of the Cretaceous-Paleogene (K-Pg) impact winter. A contribution to the discussion

Abstract

Abstract The Cretaceous-Paleogene (K-Pg) boundary Chicxulub impact is supposed to have produced a nearly decade-long impact winter which resulted in a mass-extinction event among dicot angiosperms but which left pteridophytes comparatively unaffected. Dicot angiosperms subsequently recovered from the soil seed bank following an episode of global deforestation, although this recovery took centuries. Pteridophytes, on the other hand, are supposed to have recovered within months of the impact event, due to the characteristic, short-term viability of fern spores in the soil bank – an interpretation consistent with the assumption that the dominant fern spore at the K-Pg boundary fern spore spike, Cyathidites Couper, was produced by cyatheaceous foliage. At the K-Pg boundary section near Sugarite, New Mexico, however, Cyathidites spores are more likely to have been produced by schizaeaceous foliage, which produces spores capable of germinating after spending about a decade or more in the soil and which already commanded similar depositional settings in western North America during the Maastrichtian. Therefore, the protracted – millennial – timescale for fern dominance in the earliest Danian could be related to the unique ecology of schizaeaceous ferns that recovered from a persistent spore bank in a habitat that they already dominated, presumably by suppressing the colonization of angiosperms.