Pyritized filamentous fungi in silicified miniature paleo-speleothems of basal Ediacaran, Weng'an, South China

Most modern fungi, though of a marine origin, live in terrestrial environment and play a crucial role in enhancing continental weathering (Heckman et al 2001, Kennedy et al 2006) and strengthening the flux of river-phosphorus (P) to ocean(Föllmi 1996) , which is the key limiting macronutrient element in marine primary productivity(Kump 2014) . The history of global phosphogenesis events reveals the first abrupt rise in flux of river-P to ocean in the late Neoproterozoic, indicating globally enhanced continental weathering(Papineau 2010) possibly resulted from fungal terrestrialization(Kump 2014) , which is predicted by phylogenetic studies ^1</a> and confirmed by geochemical data(Kennedy et al 2006, Knauth & Kennedy 2009, Kump 2014). Fungi have an evolutionary deep root recorded by fossils and suggested by molecular evidence, ~1500-900 Ma (million years ago)(Heckman et al 2001, Loron et al 2019) or may even as early as 2400 Ma(Bengtson et al 2017). But it is not known when fungi first colonized the land and thereafter impacted the Earth surface environment. Here, we report the in-situ pyritized fungal microfossils with aseptate hyphae and spores, reconstructed by transmitted light microscopy and synchrotron radiation X-ray tomography. The fossil fungi are preserved in siliceous cements of paleo-karstic speleothems in sheet-cracks from the basal Ediacaran cap dolostone of the Doushantuo Formation(~635 Ma)(Condon et al 2005, Zhou et al 2019) at Weng'an, South China. The broad and transient (< 6.2 ka) paleo-karstification at ca. 635 Ma, which is caused by uplifting of continental shelf owing to deglacial isostatic rebound(Zhou et al 2010, Zhou et al 2017), forced microbe to terrestrial environment and developed in subsurface miniature speleothems. Our discovery provides direct fossil evidence for early colonization of land by fungi, which may lead to increasing marine phosphorus levels and primary productivity in early Ediacaran Ocean, subsequently elevating atmospheric oxygen(Sahoo et al 2012) and eventually the expansion of marine complex life(Shen et al 2011).