NORTH AMERICAN PARATROPICAL FLORAL EXTINCTION IN THE LATE PALEOCENE-EARLY EOCENE

The Palaeocene—Eocene Thermal Maximum (PETM) at ≈55.8 Ma marks a transient (≈100 ky duration) interval of rapid greenhouse warming that had profound effects on marine and terrestrial biota. Plant communities at high latitudes responded rapidly with major but transient compositional turnover. The long-term effects on tropical vegetation communities that stem from the brief period of global warming are unclear. We present pollen data from the paratropical U.S. Gulf Coast (eastern Mississippi, western Alabama and Georgia) which had background Palaeogene mean annual temperatures of 26-27 °C. Sporomorph data (pollen and spores) demonstrate that taxonomic diversity increases over ≈1 my in the Late Palaeocene but this trend is replaced, with the first occurrences of taxa that mark the Early Eocene (e.g. Granulatisporites luteticus, Nuxpollenites psilatus, Interpollis microsupplingensis, and Brosipollis spp.), by a pronounced extinction into the Early Eocene ≈20% of the palynoflora). Taxonomic diversity also decreases by up to 38% in the Early Eocene. The timing of the extinction is not clearly resolved but may be restricted to the earliest part of the Early Eocene. Two richness estimators (Chao 2 and Jackknife 2) both demonstrate that Late Palaeocene samples contain significantly more taxa than those in the Early Eocene. However, these estimates are compromised in part by the varying amounts of time contain within each bin. Extinction on the U.S. Gulf Coast proves that ancient tropical ecosystems were highly susceptible to changes in diversity mediated directly or indirectly by environmental change even during equable greenhouse climates in the early Palaeogene.