Plants and palynomorphs from the Lower Devonian (upper Emsian) of the Holy Cross Mountains, Poland

Abstract

We present a preliminary assessment of a new Lower Devonian biota from an exposure of the Zagórze Formation at Bukowa Góra quarry in the Łysogóry Region of the Holy Cross Mountains, Poland. Abundant plant macrofossils preserved as carbonaceous compressions, adpressions, and permineralizations occur alongside a diverse assemblage of microfossils. Palynostratigraphic analysis places the fossiliferous sequences in the narrow Pro. Zone within the AP Zone of the douglastownense-eurypterota Miospore Zone, which corresponds to the upper part of the Emsian. Palynofacies analysis confirms that these sediments formed in a shallow-water, alluvial environment. The biota contains a rich assemblage of freshwater and brackish water organisms and fully terrestrial ones. Common elements include filamentous green algae, arthropods, terrestrial fungi-like filaments, nematophytes and abundant land plants. Scolecodonts and acritarchs are much rarer, suggesting limited marine influence. The new flora contains stem-group vascular plants, lycophytes and euphyllophytes. Among the permineralized remains is some of the earliest evidence of complex vascular systems, including cruciform and plate-like stelar organizations and secondary wood. We record the earliest fossil evidence of a dissected stele of the cladoxylopsid type. Innovations such as these were fundamental to the later evolution of arborescent growth in plants and the development of forest ecosystems. The biota complements and extends our knowledge of Emsian biotas in Euramerica just prior to the rapid changes that marked the Middle Devonian. It provides insights into a diverse early terrestrial community and raises further questions about the affinities and roles of arthropods and nematophytales in these ecosystems.