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

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 Glade of eophytes. Here we present an unprecedented comprehensive survey of hundreds of charcoalified eophytic mesofossils from a Lower Devonian (Lochkovian) Lagerstatte 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. (C) 2021 Published by Elsevier B.V.

Automated summary

The discovery of land plant spores with unique configurations in Middle Ordovician rocks suggests a pioneering phase of plant evolution before trilete spore-bearing tracheophytes. A new Glade of eophytes has been identified in Upper Silurian and Lower Devonian examples, possessing characteristics of both tracheophytes and bryophytes. Charcoalified eophytic mesofossils from the Lower Devonian in the UK reveal a wide range of branching forms with conducting cells, indicating their role in nutrient transport. These small plants were an important component of Early Devonian vegetation but disappeared as larger vascular plants diversified.