Abstract Massive occurrences of microbialites near the Permian–Triassic boundary have been interpreted as being due to benthic microbial proliferation in unusual marine conditions after the end-Permian mass extinction. Here, we present large populations of Polybessurus-like microfossils in the microbialites of the South China Craton to reveal their morphological structures, growth patterns, and ecological implications. These distinctive microfossils are composed of layered stalks and spherical endpoints. The spheroids, 20–40 μm in diameter, comprising external thin micritic walls and internal sparry parts, are interpreted as coccoid cyanobacteria. The stalks consist of multiple “stacked-cup” micritic envelopes consisting of micron-sized magnesian calcite/dolomite grains and are catalogued as calcified remains of coccoid cyanobacterial extracellular polymeric substances (EPS). Early microbially mediated calcification of EPS increased the preservation potential of microfossils. The microfossils stand upright as coccoid unicells supported by the highly unidirectional secretion of EPS, revealing their benthic behaviours. The successively secreted EPS lift the cells away from the substrate, expanding their ecological niches to gain more sunlight for photosynthesis in the barren marine floor. The distinctive Polybessurus-like microfossils can be viewed both in laminae of stromatolites and in spotted/digitate clots of thrombolites, suggesting their critical roles in microbe-dominated reefs in the aftermath of the end-Permian mass extinction. The morphological features and growth patterns of the Polybessurus-like fossils resemble their Proterozoic counterpart—Polybessurus bipartitus Fairchild ex Green et al. (1987) . The widespread Polybessurus-like fossils in the Permian–Triassic boundary microbialites of the South China Craton suggest pervasive retrogressive ecosystems on carbonate platforms after the largest extinction event during the Earth's history.

中文翻译：

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类 Polybessurus 化石是华南二叠纪-三叠纪边界微生物岩的主要贡献者

摘要 二叠纪-三叠纪边界附近微生物岩的大量出现被解释为是由于二叠纪末大灭绝后异常海洋条件下的底栖微生物增殖所致。在这里，我们展示了华南克拉通微生物岩中大量的类 Polybessurus 微化石，以揭示它们的形态结构、生长模式和生态意义。这些独特的微化石由分层的茎和球形端点组成。直径为 20-40 μm 的球体由外部薄泥晶壁和内部喷射部分组成，被解释为球状蓝藻。茎由多个“堆叠杯”泥晶包络组成，由微米级镁质方解石/白云石颗粒组成，并被归类为球状蓝藻细胞外聚合物（EPS）的钙化残留物。早期微生物介导的 EPS 钙化增加了微化石的保存潜力。微化石作为球状单细胞直立，由 EPS 的高度单向分泌支持，揭示了它们的底栖行为。连续分泌的 EPS 将细胞从基质上抬离，扩大它们的生态位，以获得更多阳光以在贫瘠的海底进行光合作用。在叠层石的薄片和凝块石的斑点/指状凝块中都可以看到独特的类似 Polybessurus 的微化石，表明它们在二叠纪末大灭绝之后以微生物为主的珊瑚礁中的关键作用。类 Polybessurus 化石的形态特征和生长模式类似于它们的元古代对应物——Polybessurus bipartitus Fairchild ex Green 等人。(1987)。华南克拉通二叠纪-三叠纪边界微生物岩中广泛分布的类 Polybessurus 化石表明，在地球历史上最大的灭绝事件之后，碳酸盐平台上存在普遍的退化生态系统。