Where the lycophytes come from? – A piece of the story from the Silurian of peri-Gondwana

Abstract

A single sterile compression matching Baragwanathia Lang et Cookson in all important morphological traits – a dichotomously branched stem densely covered with sub-parallel abaxially slightly bent linear microphylls partly truncate and partly rounded at tips – was discovered in the upper Silurian Požáry Formation at Karlštejn in the Barrandian area (Czech Republic). The fossil is assigned to a new species Baragwanathia brevifolia Kraft et Kvaček, sp. nov. and its stratigraphical position is dated by co-occurring graptolites (lower Přídolí, Neocolonograptus ultimus Biozone). Due to the compression and high degree of coalification, no anatomical data are available to prove unambiguously the affinity to vascular plants but medial strands in microphylls indicate thicker tissue of a single midrib unknown in algae. Although the studied fossil recalls superficially hemichordates (graptolites) or hydroids this view is demonstrably denied by several reliable characters. A part of the stem is covered by epibiontic fauna (bryozoans and brachiopods) proving that it dwelled submerged in marine water environment. Based on the attached epibionts an attempt is made to visualize the life mode of this plant as growing in marine environment and possibly stretching out of the water by parts not colonized by epibionts. All direct and indirect evidences convincingly indicate the fossil to be an aquatic precursor of dry-land microphyllous plants, i.e. lycophytes. It is a significant piece of puzzle to the global high-resolution paleogeography of the Gondwanan margin.