Microfossils from the Paleoproterozoic Hutuo Group, Shanxi, North China: Early evidence for eukaryotic metabolism

The Paleoproterozoic Hutuo Group is well-developed and distributed in the Wutai Mountains in the Xinzhou area of Shanxi Province, North China. Its middle part - the Dongye Subgroup is more suitable for obtaining microfossils in deposited sediments characterized with sandstone or slate in the lower part, and upward into interbedded sandstone, carbonate with stromatolites and phyllite. Based on recent zircon dating, the Hutuo Group was deposited around 2150–1950 Ma. In this study, eight morphological genera of microfossils, including the spheroid and filamentous cyanobacteria Eoentophysalis, Sphaerophycus, Siphonophycus, Pseudodendron, and the acritarchs Dictyosphaera, Dongyesphaera gen. nov., Leiosphaeridia, Satka were identified from the Wenshan, Hebiancun and Tianpengnao Formations of the Dongye Subgroup. The identified microfossils reveal that eukaryotic protists exercised metabolic activities rarely observed to have occurred in what are thought to have been suitable environments.