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 Sigiltaria 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. ichthyotepis 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 Sigiltaria stems could be interpreted as juveniles of the larger Sigillaria trees. Two new morphospedes 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. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

Thin arborescent lycopsid axes belonging to the genus Sigiltaria were discovered in Inner Mongolia, China, showing major differences from previously known taxa. Two new morphospedes, Sigillaria pfefferkornii sp. nov. and Sigillaria wudensis sp. nov., were identified among the thin axes, indicating more diversity in the Permian Sigillaria species in Cathaysia than previously understood. The study provides insights into evaluating early and late ontogenetic stages of plants and highlights the lack of an accurate search image for juvenile arborescent lycopsids.