FLORAL DECLINE AND RECOVERY ACROSS THE-K-PG BOUNDARY INVESTIGATED THROUGH NEONTOLOGICALLY-INFORMED PHYTOLITH EXTRACTION AND IDENTIFICATION

The end-Cretaceous mass extinction event represents one of the most significant periods of ecological turnover in Earth's history. Plants—the base of the terrestrial trophic pyramid—played a critical role in shaping whole-ecosystem decline and recovery during this event, but the nuances of their role remain ambiguous. Paleobotanical studies over this interval have relied on two deep-time proxies; megafloral fossils and palynological fossil pollen grains. Like all paleontological proxies, these investigative avenues have inherent preservational limitations and biases. Phytoliths, microscopic, intra-plant silica bodies, represent a potential additional proxy that provides a more localized perspective of paleobotanical diversity than windborne, geographically-averaged pollen while preserving in a broader range of environments than megafloral fossils. Here, I supplement previous studies by employing phytoliths as a novel proxy for studying paleofloral shifts across the K-Pg boundary. The application of phytoliths in the fossil record as a tool to deduce paleofloral composition has been hindered by poorly-established taxonomic associations between phytolith morphology and source plant identity—the diagnostic forms of gymnosperms in particular are virtually unknown. I addressed this obstacle by comprehensively cataloging characteristic phytolith morphotypes of gymnosperm families, thereby elevating this ancient clade to a level of sampling comparable to the well-studied angiosperms. This resulted in a comparative dataset informing preliminary analyses of Cretaceous and Paleogene phytoliths from Hell Creek and Fort Union formation sediments. Quantitative and qualitative differences in recovered phytolith assemblages from pre and post K-Pg boundary samples are discussed in the context of their stratigraphic and paleoecological significance and compared to the results of previous megafloral and palynological proxy studies. The integration of phytoliths into paleobotanical study contributes to a developing, novel analytical paradigm for studying ecological change in the fossil record, providing a holistic biological perspective of major events in Earth’s history.