The limits of life revealed in a silicified micro-ecosystem: Sphenophyllum stems, leaves, and roots trapped inside an arthropod boring in a Permian calamitalean

limits of life revealed in a silicified micro-ecosystem: Sphenophyllum stems, and roots trapped inside an arthropod boring in a Permian calamitalean. Palaeontographica Abteilung Abstract One of the youngest known occurrences of anatomically preserved Sphenophyllum Brongniart 1828 is reported from the Permian Motuca Formation, Parnaíba Basin, central-north Brazil. At least 31 stems, densely interwoven to each other and associated with tiny roots and leaves of this extinct herbaceous sphenopsid, were found in a silica-petrified state. Originally grown upright, they squeezed into in the pith of the arborescent calamite Arthropitys barthelii N EREGATO et al. 2017, which was additionally caved by putative xylophagous herbivores. Although restricted within natural limits, the Sphenophyllum organs show different developmental stages that encompass a majority of juvenile stems and a few ones with initial secondary growth. The stems are of circular to elliptical outline and consist of a central triarch actinostele made of primary vascular tissues and a variable amount of wood. Extraxylary tissues comprise a narrow innermost zone with putative phloem, internal periderm made of