Linking fern foliage with spores at the K-Pg boundary section in the Sugarite coal zone, New Mexico, USA, while questioning the orthodoxy of the global pattern of plant succession across the K-Pg boundary

摘要

The Cretaceous-Paleogene (K-Pg) mass-extinction event had a profound effect on global vegetation, with a major turnover. The post-extinction flora is typified by a recovery succession dominated by fern spores (Cyathidites and Laevigatosporites). Dispersed spores of the genus Cyathidites in this fern-spore spike interval are commonly assumed to have been produced by tropical tree ferns. However, Anemia-like schizaeaceous foliage is also known to have produced Cyathidites (psilate, Lygodium-like trilete spores) in the Paleogene. Within the Sugarite coal zone of the Raton Formation, which contains both the K-Pg boundary and the fern-spore spike, Anemia-like schizaeaceous foliage currently classified as A. elongata (NEWBERRY) KNOWLTON is associated with Cyathidites spores. As no other fern megafossil that has been collected from the Sugarite coal zone is known both to have survived the K-Pg mass-extinction event and to have been capable of producing spores of the dispersed spore genus Cyathidites, it is hypothesized that A. elongata produced these spores. A. elongata is found alongside species with a strong affinity to Lauraceae, which dominates the post-extinction dicot angiosperm flora in the Raton Basin. Lauraceous pollen typically is not preserved in the fossil record. Therefore, the orthodox concept of an earlier, fern-dominated recovery interval followed by a later phase of angiosperm recovery, which is principally based upon palynology, is questioned. Reevaluation of the classic model for plant recovery in the Raton Basin, which was based upon the pattern of plant recolonization of the Krakatau islands following the 1883 volcanic eruption, provides support for the novel concept that recolonization by Lauraceae may have preceded or, more conservatively, coincided with recolonization by schizaeaceous (Cyathidites-producing) or thelypteridaceous (Laevigatosporites-producing) ferns.