Age-controlled south polar floral trends show a staggered Early Triassic gymnosperm recovery following the end-Permian event

Abstract

The end-Permian event (EPE, ca. 252.3–251.9 Ma) led to the generalized collapse of gymnosperm-supported ecosystems. They eventually recovered despite Early Triassic suppression and became globally dominant for most of the Mesozoic. Understanding the sequence and timing of gymnosperm reestablishment at different latitudes is therefore key to explaining how they regained their foothold. Given the limited data on polar plant communities, here we present the first high-resolution, age-controlled floristic trends from the high southern latitudes (Sydney Basin, Australia; ∼70°S) from the latest Permian to the Middle Triassic. Sedimentological and biostratigraphic data and stable carbon isotope ratios of organic matter were used to establish lithostratigraphic correlations, paleoenvironmental insights, and links to the global chronostratigraphy. Non-metric multidimensional scaling of spore-pollen groupings confirmed that the late Smithian thermal maximum (LSTM, ca. 250.3–249.6 Ma) and the Smithian-Spathian event (SSE, ca. 249.6–249.2 Ma) were the primary drivers of significant Early Triassic ecosystem changes in the Sydney Basin. Following the EPE, ecosystems supported by peltasperm seed ferns were the first to establish, lasting for ∼200,000 years. Voltzialean conifers were thereafter dominant for ∼1.5 million years until the LSTM. Stress-tolerant cosmopolitan pleuromeian lycophytes then became the predominant flora, lasting ∼800,000 years until SSE-associated cooling allowed umkomasialean seed ferns to expand, which persisted and ultimately characterized Middle-to-Late Triassic high-latitude Gondwanan ecosystems. Global comparisons showed that pleuromeians surged under extreme post-EPE conditions, but their rise was delayed by ∼1.7 million years in the polar south. Our findings support the hypothesis that the post-EPE interval was a staggered process rather than one of monotonic recovery, with gymnosperm and lycophyte floral communities waxing and waning in succession until the early Middle Triassic.