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Paper No. 228-6
Presentation Time: 9:25 AM
ECOSYSTEM ENGINEERING FEEDBACK AND THE CARBONIFEROUS RAINFOREST COLLAPSE
The Pennsylvanian (323-299 million years ago) is famous for its peat-forming swamps, which spanned large parts of Euramerica during the glacial intervals of the Late Paleozoic Ice Age’s glacial-interglacial cycles. During the Early and Middle Pennsylvanian, arborescent lycopods were dominant in the wetter parts of these swamps. Suitable habitat for the swamp communities shrank with each interglacial, as climate changed from everwet to more seasonal. With each subsequent glacial interval and the associated shift to wetter conditions, we see reconstitution of remarkably similar plant communities. This changed during the transition from the Middle to Late Pennsylvanian—an interval known as the Carboniferous Rainforest Collapse. Following the extinction of all but one genus of the arborescent lycopods, parts of the swamps previously inhabited by lycopods became dominated by marattialean tree ferns. Here, we investigate the timing and patterns associated with this ecological crisis. We utilize the Phillips Coal Ball Collection dataset, an extensive paleobotanical dataset derived from the observation of thousands of coal ball peels—acetate “thin sections” made from permineralized nodules of peat that preserve the tissues and organs of the vegetation in anatomical detail. Our results indicate the genus diversity of all major plant taxonomic groups was negatively impacted by this crisis. Moreover, we find evidence that the crisis is a protracted interval, spanning multiple glacial-interglacial cycles prior to the Middle-Late Pennsylvanian boundary. These results are supported by patterns in dominance-diversity, ecological evenness and dissimilarity, survivorship, and changes in genus-composition. Lastly, we discuss a potential ecosystem engineering effect by which arborescent lycopods may have helped create their own suitable habitat. We propose that the breakdown of this effect, via the crossing of some ecological threshold, may have been crucial in driving this crisis.