The megafossil plant record

In the northern and southern humid climatic zones of the supercontinent Pangea (fig. 1), the dieback of end-Permian woody vegetation resulted in the widespread disappearance of peat forests. In the semi-arid equatorial Euramerican floral province, which was characterized by conifers and seedferns prior to the crisis, dominant conifer taxa became extinct close to the Permian-Triassic boundary. Earliest Triassic megafossils are rare because of unsuitable lithologies for plant preservation. We do know that among the surviving plants, lycopods played a central role. In the absence of larger gymnosperms, the early Triassic vegetation became increasingly dominated by a variety of relatives of modern quillworts. In many places in the world quillwort dominance ultimately resulted in large populations of the tall species Pleuromeia sternbergii (fig. 2). This is remarkable, because quillworts formerly play a modest role in the pre-crisis plant communities. Just like their recent relatives (Isoetaceae, fig.3), they were possibly amphibious species, with poor competitive abilities, but with a high stress-tolerating capacity. In Europe this tree-less vegetation persisted for the remarkably long period of about 4 to 5 million years, between ~251 and 246 million years ago. Several European megafossil findings show a replacement of Pleuromeia by Voltzia-conifers dominated communities during the transition from Early to Middle Triassic.