Picking up the pieces: New charcoalified plant mesofossils (eophytes) from a Lower Devonian Lagerstӓtte in the Welsh Borderland, UK

• Published in: Review of palaeobotany and palynology 2022-02, Vol.297, p.104567, Article 104567
• Main Authors: Edwards, Dianne, Morris, Jennifer L., Axe, Lindsey, Duckett, Jeffrey G.
• Format: Article
• Language: English
• Subjects: Cryptospores; Early embryophytes; Eophytes; Lower Devonian; Mesofossils
• ISSN: 0034-6667; 1879-0615
• DOI: 10.1016/j.revpalbo.2021.104567

The discovery of land plant spores with permanent tetrad and dyad configurations in Middle Ordovician rocks indicated a pioneering phase of phytoterrestrialisation that predated trilete spore-bearing tracheophytes. Limited studies on Upper Silurian and Lower Devonian examples suggest that the producers possessed characters of both tracheophytes and bryophytes, leading to the erection of a new clade of eophytes. Here we present an unprecedented comprehensive survey of hundreds of charcoalified eophytic mesofossils from a Lower Devonian (Lochkovian) Lagerstätte in the Welsh Borderland, UK, which reveals a wide range of branching in smooth axes with occasional stomata and conducting cells interpreted as predominantly involved in nutrient transport. Similar anatomy was discovered in fossils with usually fragmentary terminal sporangia containing evidence for permanent cryptospores. This raises the possibility that these small sporophytes of narrow axial diameter exhibited matrotrophy although the nature of the autotrophic gametophytes remains elusive. The sheer numbers of these tiny mesofossils in the fine-grained rocks at the locality indicate that these small plants were an important part of vegetation in Early Devonian times – a component that disappeared as vascular plants diversified and increased in size. Whether or not the pioneering Ordovician vegetation had exactly similar characteristics requires more information of gross morphology and anatomy of fossils in the intervening years. •Descriptions of architecture and anatomy of a new lineage of early land plants.•The Eophytidae were minute plants with characters of tracheophytes and bryophytes.•Distinction of about 20 species producing cryptospores in terminal valvate sporangia.•Ultrastructure of conducting cell walls closest to bryophyte food-conducting cells.•Abundance of eophytes in the assemblage indicates an important vegetational component.