Revising Palynostratigraphic Concepts in the Raton Basin a Half-century after R.H. Tschudy’s Pioneering Work: A New Pollen Proxy for the Campanian-Maastrichtian Stage Boundary and Reevaluation of the Famous K-PG Fern-Spore Spik
— Keith Berry, Spencer G. Lucas, and Paul L. Sealey

R.H. Tschudy pioneered palynostratigraphy in the Raton Basin nearly a half-century ago and established two key precedents: (1) that the Campanian-Maastrichtian stage boundary should be placed at or near the first appearance datum (FAD) of Kurtzipites and (2) that the Cretaceous-Paleogene (K-Pg) boundary fern-spore spike signaled the comparatively rapid recovery of ferns following the K-Pg impact event. In light of new discoveries, revisions to these key concepts are proposed. First, correlation between the Raton Basin and the Rock Springs uplift in Wyoming indicates that the pollen proxy for the Campanian-Maastrichtian stage boundary should be moved lower, to within the uppermost part of the Trudopollis meekeri Zone (formally defined as an Interval Zone between the FAD of Aquilapollenites striatus and the LAD of T. meekeri). Second, the apparent association of Cyathidites spores with Anemia-like schizaeaceous foliage and Laevigatosporites spores with thelypteridaceous foliage in the Raton Basin suggests that it was not a general property of ferns, such as the ability to regenerate rapidly from short-lived spores or rhizomes in the soil spore bank, which conferred an advantage in the harsh, post-impact world of the earliest Danian. The long-term viability of modern Anemia, Lygodium, and Thelypteris spores contrasts with that of modern cyatheaceous and Blechnum ferns (the taxa traditionally associated with the dominant fern spores at the K-Pg boundary), presumably accounting for the monotaxial nature of the two-phase fern-spore spike in the Raton Basin. Thus, spores of these ferns could have survived a decade-long impact winter, which has been suggested to have caused a mass-extinction event among dicot angiosperms.