中国科学院南京地质古生物研究所机构知识库

Stigmaria is the rooting organ of late Paleozoic arborescent lycopsids. Previous scientific considerations of the stigmarian habit have placed the entire rooting organ shallow beneath the substrate surface, despite the proximal main stigmarian axes radiating outwards orthogonally from the trunk in all known stump casts with attached Stigmaria. Here, we show definitively that stigmarian axes were subaerial proximally given both their preservation within and direct interaction with two independent volcanic ash layers. However, it remains uncertain whether these axes dove under the substrate surface distally and, if so, where along the axes this occurred. We test the aboveground or belowground nature of distal stigmarian axes with comparisons of sampling frequencies of vasculature from different regions of the arborescent lycopsid body plan as preserved in 'coal ball' permineralization fossils from the Pennsylvanian of Euramerica. The overabundance of root versus shoot material has previously been recognized as evidence of the enhanced preservation potential of organs growing within, rather than above, the substrate. We find that specifically the terminal stigmarian axis vasculature is overrepresented in the fossil record compared to trunk and proximal stigmarian axis vasculature, suggesting that the primary stigmarian axes and their secondary branches grew on the substrate before eventually going underground distally. Implications for arborescent lycopsid establishment are considered. (c) 2023 Elsevier B.V. and Nanjing Institute of Geology and Palaeontology, CAS. All rights are reserved, including those for text and data mining, AI training, and similar technologies.