Two new species of Sigillaria Brongniart from the Wuda Tuff (Asselian: Inner Mongolia, China) and their implications for lepidodendrid life history reconstruction

Thin (3–6 cm) arborescent lycopsid axes that conform to the genus Sigillaria have been discovered upright in situ in the Wuda Tuff (Asselian: Inner Mongolia, China). Given that a broad lycopsid tree, Sigillaria cf. ichthyolepis, was the sole arborescent lycopsid taxon previously known from the assemblage, the new fossils were initially assumed to be juveniles of S. cf. ichthyolepis when assessed in the field under active mining conditions. Following retrieval of these specimens, further observation indicated that major discrepancies exist between the surface morphology of these smaller axes and that of S. ichthyolepis. Additionally, anatomical and morphological features of the trunks preclude all possible geometric transformations by which the small Sigillaria stems could be interpreted as juveniles of the larger Sigillaria trees. Two new morphospecies of Sigillaria are recognized from among the thin axes: stems of Sigillaria pfefferkornii sp. nov. and of Sigillaria wudensis sp. nov., the first two sub-canopy species of the genus. This investigation provides a methodology for evaluating whether two fossils may represent early and late ontogenetic stages of the same plant and suggest that we lack an accurate search image for juvenile arborescent lycopsids given that the sapling model fails here. Additionally, the major group of Sigillaria species surviving into the Permian in Cathaysia was more diverse, both taxonomically and ecologically, than previously understood. •Thin Sigillaria specimens from the Wuda Tuff are not saplings of S. ichthyolepis.•Two new morphospecies are described from these specimens.•A test to determine if an individual is a juvenile is presented.•Sigillaria in the Permian of Cathaysia was taxonomically and ecologically diverse.