Siluro-Devonian landscapes of southern Britain: the stability and nature of early vascular plant habitats

A prerequisite for plant taphonomy and palaeoecological analysis of early land plants is to understand the palaeogeomorphology of the landscapes that they inhabited. The Lower Old Red Sandstone of the Anglo-Welsh Basin was chosen to ascertain the nature of the landscapes and range and variability of potential plant habitats. Evidence is provided for dynamic, low-lying landscapes, with complex hydrology and mosaics of microenvironments. The Raglan Mudstone Formation (latest Pridoli-earliest Lochkovian) represents a mud-dominated, ephemeral dryland river system, active during short-lived high-discharge events. Plant habitats were restricted to areas with temporarily elevated water tables, suitable for plants with short life cycles (e.g. rhyniophytes). The St. Maughans Formation (early Lochkovian) represents a sand-dominated, perennial trunk channel river system, with an overall wetter, more stable landscape. Plant habitats extended into areas of permanently elevated water tables, where plants with a more extensive vegetative growth stage survived (e.g. zosterophylls). In association with evidence from the plant fossil record, this leads to the hypothesis that during the latest Silurian to earliest Devonian the landscapes across the southern margins of Laurussia were too hostile (overall moisture deficient and unstable) for plants of higher organization than rhyniophytes to establish, despite their radiation across palaeoequatorial latitudes much earlier.