Trends in plant diversity and ecology in the Euramerican Pennsylvanian tropics

The Phillips Coal Ball Collection (PCBC) represents one of the largest paleobotanical datasets in existence. The collection contains over 50,000 coal balls-permineralized carbonate nodules that capture, in cellular detail, wetland plants in the Euramerican tropics during Pennsylvanian and early Permian glacial intervals. Over 800,000 square-centimeters of the coal ball material has been analyzed microscopically, with researchers quantifying taxon, tissue type and plant organ abundance for material from over fifty localities. We have recently re-digitized much of this historic dataset (see: Looy et al. in this session for details) and here present some of our preliminary results. We analyzed the PCBC dataset, looking at trends in diversity through space and time, as well as how those trends relate to glacial-interglacial cycles and long-term aridification. Our preliminary results recapitulate previously described patterns in extinction/extirpation and origination/immigration, as well as changes in ecological dominance, at the Middle to Late Pennsylvanian transition (a.k.a. the Carboniferous Rainforest Collapse or "CRC"). These results provide a more nuanced understanding of this paleobotanically important interval. While lycopods are by far the hardest-hit clade during the transition, all major plant groups-including the ferns, which go on to dominate much of the Late Pennsylvanian tropical peat swamps-experience elevated extinction/extirpation rates and low origination/immigration rates during the CRC. In addition, we elucidate ecological changes related to shifts in dominance-diversity trends at this transition; specifically, we highlight how changes in landscape composition likely had significant effects on paleowildfire.