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A recently excavated field near the hamlet of Craswall in Herefordshire, south of Hay-on-Wye, has yielded abundant fossil plants. They are preserved in sandstone and siltstone beds as coalified compressions, for the most part lacking anatomical detail, and as iron-stained impressions. Also present are fish including Rhinopteraspis crouchi, which places the exposure in the middle to upper Lochkovian (Lower Devonian), plus prototaxalian nematophytes and Pachytheca. The commonest plants, which cover bedding planes, are randomly arranged sterile axes that rarely branch. They are interspersed with Salopella, fragmentary strobili of the Zosterophyllum cf. fertile complex and a number of taxa with more isodiametric sporangia borne terminally on isotomous or anisotomous branching systems. New circumscribed taxa include: Monnowella bennettii, a rhyniophytoid, with single sporangia terminating unbranched laterals on a weakly anisotomously branching system; and Craswallia haegensis, a possible zosterophyll, comprising bivalved elliptical sporangia, borne distally on stout unbranched stalks.\ud \ud Newly found fossils from a second, slightly younger locality at Newton Dingle, Shropshire, include Zosterophyllum sp. Together with specimens previously described from the same site, comparisons of Zosterophyllum from the two localities are made.\ud \ud In common with other assemblages in the Anglo-Welsh Basin, the plants described here show more derived architecture and fertile characteristics than are present in older Přídolí (Silurian) representatives. An increase in size and complexity of branching, with concomitant changes in light harvesting, reproductive capacity and spore dispersal efficiency, is noted in taxa from increasingly younger Lochkovian to Pragian strata. These changes are interpreted as responses to increased competition for light and space in early terrestrial ecosystems, which resulted in the local extinction of the rhyniophytes and diversification of the zosterophylls. |
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