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Plant diversity in the Early Devonian – stratigraphic and geographic patterns
The Early Devonian epoch (419.2 ±3.2-393.3 ±1.2 Ma) (Gradstein 2012) marked the commencement of a rapid evolutionary radiation and increase in the diversity and complexity of basal tracheophytes and other groups of land plants. While the importance of the Early Devonian to the radiation of early land plants cannot be overstated, a comprehensive database compiling the most current knowledge of this flora has been lacking. Using a newly revised taxonomic system of Early Devonian land plants, this study seeks to assemble all Early Devonian records of tracheophytes and related land plants into one database in order to assess the geographic and stratigraphic patterns of plant diversity during this interval. Records were cross-referenced with previous analyses and other databases to ensure that the nomenclature, ages, locations, and other data reported for each record are as accurate and current as possible. The locations of fossil assemblages were plotted on both present-day and Early Devonian maps. The Early Devonian paleoflora was characterized by high levels of endemism among Incertae sedis taxa, zosterophyllopsids, and rhyniopsids, and a varied flora spread across six or possibly seven floristic provinces. Taxonomic richness was lowest during the Lochkovian which was dominated by Incertae sedis taxa and rhyniopsids, especially in Laurussia. Both genus and species richness peaked during the Pragian when zosterophyllopsids dominated the floras of most provinces. Overall taxonomic richness declined considerably during the Emsian, although taxonomic richness peaked in Laurussia and Siberia during this stage, largely as a result of the dominance of euphyllophytes. The database created for this study contains a total of 1325 records of 185 genera and 305 species distributed within 357 assemblages and forms the most comprehensive compilation of Early Devonian land plant records to date. The results of this study will provide a basis for future studies aimed at better understanding the patterns of evolutionary radiation in early land plants.