ENVIRONMENTAL IMPLICATIONS OF A MIDDLE PENNSYLVANIAN DICRANOPHYLLUM LEAF FROM THE ILLINOIS BASIN (INDIANA, USA)

Abstract During the Middle Pennsylvanian Subperiod, glaciers repeatedly expanded and retreated over the southern polar regions of Gondwana. These glacial cycles were reflected in corresponding sea-level and climatic changes in the tropical lowlands of Euramerican Pangaea. Climate alternated between humid, peat-/coal-forming periods and seasonally dry intervals. Organic remains are generally underrepresented in the fossil record of seasonally dry periods due to poorer preservational conditions. One enigmatic, seasonally dry-adapted genus of plants is Dicranophyllum, a coniferophyte or basal conifer with distinctive bifurcating leaves. Here we present a Dicranophyllum sp. leaf from a deltaic facies of shales above the Pirtle Coal in the Shelburn Formation, McLeansboro Group in the Illinois Basin, Indiana, USA (Desmoinesian Stage, Middle Pennsylvanian), the first and only representative of this genus known from the region. Due to the genus’ near absence from humid climate-associated coal layers, paired with the lack of surrounding uplands in the Illinois Basin, this specimen provides further support for the hypothesis of alternating climatic regimes during the Middle Pennsylvanian.