WETLANDS PALEOECOLOGY OF THE MIDDLE AND LATE DEVONIAN

The early history of wetland plant communities is synonymous with that of early land plants, since the earliest stages of land plant evolution took place along aquatic margins. Early wetland communities can all be characterized as siliclastic until the Middle and Late Devonian, when the earliest known peat accumulations occurred. Evidence for these peat accumulations are found as thin coal layers in West Virginia, Virginia, Melville Island of Arctic Canada, and Bear Island of Arctic Norway. The plants that contributed to these peat accumulations vary among sites, are monotypic, and are from widely disparate clades such as tree lycopsids, the zygopterid fern Rhacophyton, and the progymnosperm Archaeopteris. These plants are also found together in Late Devonian siliclastic wetland deposits, such as the Red Hill locality in the Catskill Formation of north-central Pennsylvania, which is interpreted as an abandoned channel oxbow lake succession. The flora at Red Hill includes Archaeopteris spp., Rhacophyton, Gillespiea, Barinophyton, gymnosperms, and lycopsids. Thus far the only evidence for extrabasinal floras in the Late Devonian comes from spores found in crevasse splay beds that split some oxbow peats. The parent plants of these spores are unknown, but are distinct from the typical suite of Late Devonian lowland plants. At Red Hill, quantitative sampling and analysis of its parautochthonous flora indicate small-scale heterogeneity of the plant community within its floodplain setting. Lycopsids representative of a new isoetalean taxon grew within the margins of the oxbow lake and formed a distinct zone of wetland adapted plants. They are the precursors of the giant lycopsids that later contributed to the vast equatorial peat swamps of the Carboniferous.