Abstract A series of vegetation changes take place in tropical ecosystems during the Pennsylvanian Subperiod. The most notable change, recognizable from palynology and plant macrofossils at the Middle and Late Pennsylvanian boundary in the Illinois Basin, is the extirpation, or local extinction, of certain lineages of arborescent lycopsids, followed by their replacement by stem group marattialean tree ferns. The leading hypothesis suggests a significant change in precipitation regime as the cause. To test this hypothesis, we examine the vascular anatomy and physiology of key lineages of Pennsylvanian plants: the sphenopsids, tree ferns, cordaitaleans, medullosans, lycophytes and extrabasinal stem group coniferophytes. Using scanning electron and light microscopy of fossilized anatomy, we provide new data on these plants’ vascular systems, quantifying their physiological capacity and drought resistance. We find that three Pennsylvanian plant lineages – the medullosans, arborescent lycopsids and Sphenophyllum – contain high hydraulic conductivity but are vulnerable to drought-induced damage, whereas others are resistant, including stem group tree ferns and coniferophytes. Relative abundance changes among these plants were likely driven by drought, and differences in water use efficiency would have amplified drought events as plant communities changed. The interaction of physiological selectivity and positive feedback between aridity and drought tolerance likely played a significant role in Late Paleozoic floral changes.

Abstract Although Permian fossils have been known from the Parnaíba Basin for two centuries, and some faunal and flora elements are well known worldwide, research on the fossil assemblages from this basin has lagged relative to other, more accessible basins. In the last decade, however, there has been a significant increase in the study of fossils from the two Permian units of the basin: the Pedra de Fogo and Motuca formations. The goal of this contribution is to synthesize and update the existing data on the Permian macrofossils from these formations, and to use them to address biostratigraphic, palaeoenvironmental and palaeogeographical questions. The Pedra de Fogo and Motuca formations are likely to be Cisuralian in age. Contrary to previous reports, there is more than one stratigraphic interval that preserves petrified fossil plants. The possible marine influence proposed for the Pedra de Fogo Formation must be reassessed based on the strongly terrestrial character of its fossil assemblages. Palaeoenvironmental and palaeoclimatic conditions are inferred to be wetter than is typically predicted for this region of the globe based on climatic modelling. Despite sharing some taxa with the Euramerican and Gondwanan biogeographical provinces, the Parnaíba Basin was likely to have been part of a distinct biogeographical province, as indicated by the high degree of endemism displayed by its Permian floras and faunas.