Floral dynamics and ecological adaptations in the Lopingian gigantopterid rainforest of South China

Abstract

Gigantopterids represents an enigmatic plant plexus from the Permian period and are of utmost significance in South China during the Lopingian prior to the Permian–Triassic mass extinctions due to their high diversity and abundance. However, it remains uncertain whether Lopingian gigantopterid rainforests were compositionally stable or underwent conspicuous changes through the Lopingian. From Guizhou Province in South China, a profusion of Lopingian gigantopterid leaves have been unearthed in recent excavations from the Longtan Formation. These seemingly suggest floristic turnover within gigantopterid rainforests, shifting from an early stage dominated by Gigantonoclea to a later phase dominated by Gigantopteris, concurrent with a significant decline in the marattialean tree-fern Pecopteris, and a change from swamp dominated to tidal flats and channel dominated depositional facies. Certain gigantopterids in these new materials from South China possessed climbing structures. Notably, leaves of Gigantonoclea are found connected with adhesive roots, hooks, or grapnels. Additionally, some prehensile branches were preserved wound around Pecopteris stems and rachises. These phenomena indicate the existence of both active and passive climbing modalities for Gigantonoclea, possibly involving a sinistral twining mode, which enriches our understanding of the ecological adaptations and behaviors of these ancient plants during the Lopingian. Pecopteris is shown to have been a supporting plant on which gigantopterids climbed.