Phosphatized microfossils from the Miaohe Member of South China and their implications for the terminal Ediacaran biodiversity decline

Abstract

The upper Ediacaran Miaohe Member (∼550 Ma) in South China is well known for exceptionally preserved macroscopic carbonaceous compression fossils (i.e., the Miaohe biota) that are pivotal in understanding the marine ecology and environment during the terminal Ediacaran Period. However, micro-organisms, which are also important biotic components of marine ecosystems, are poorly documented and largely limited to simple leiospheres and filaments in the Miaohe Member and equivalent strata in South China and around the world. Here we report a moderately diverse assemblage of cellularly preserved microfossils from phosphorites and siliceous phosphorite nodules and bands of the Miaohe Member at the Maxi section, Hubei Province, South China. Ten named species of eight genera, four open nomenclatures, and two unnamed taxa have been identified, including several multicellular algal fossils and various coccoidal and filamentous cyanobacteria. Abundant spheroidal fossils are morphologically analogous to Megasphaera, which has previously been interpreted as a putative metazoan embryo. Together with previously described microfossils from equivalent strata of Miaohe Member, these microfossils expand our understanding of the evolution of marine ecosystems prior to the Cambrian explosion. The late Ediacaran Maxi assemblage and the early Ediacaran Weng’an biota, both preserved through phosphatization, share several taxa. Notably, Doushantuo-Pertatataka-type acanthomorphs (DPAs) are absent from the Maxi assemblage but abundant in the Weng’an biota, consistent with a late Ediacaran decline of DPAs, which may have ushered in the terminal Ediacaran decline of soft-bodied macro-organisms of the Ediacara biota during the Kotlin crisis or in the last 10 million years of the Ediacaran Period.