Organic-Walled Microfossils from the Late Paleoproterozoic Gaoshanhe Group in North China

The emergence of eukaryotes represents one of the most remarkable events in the evolutionary history of life. Although molecular clock data have suggested that eukaryote originated no later than the Paleoproterozoic, eukaryotic fossils from this interval remains poorly understood, hampering a comprehensive understanding on the early eukaryotic evolution. The late Paleoproterozoic Gaoshanhe Group, exposed along the southern margin of the North China, represents one of the few well-preserved sedimentary archives critical for understanding early eukaryotic life. However, its fossil record remains inadequately documented. In this study, we present a systematic paleobiological investigation of organic-walled microfossils (OWMs) from the Gaoshanhe Group, using low-manipulation maceration techniques. Totally 20 mudstone samples have been processed, all of which are fossiliferous and rich in OWMs. Preliminary taxonomic identifications reveal the presence of morphologically complex taxa, including Dictyosphaera, characterized by articulated ornamentations on vesicle surface; possible Tortunema that is characterized by alternating dark and light-coloured annular bands on the vesicle wall; and Changchengonema defined by opaque filament with pseudo-branches. These preliminary data indicate that the Gaoshanhe Group preserves a diverse assemblage of early eukaryote microfossils. Future work will focus on a comprehensive systematic investigation on taxonomic diversity of the Gaoshanhe Group. In addition, we will evaluate the biological affinities of morphologically complex taxa using scanning electron microscopy (SEM), Raman spectroscopy, and Fourier-transform infrared spectroscopy (FTIR) to characterize their ultrastructural and biochemical features. These analyses aim to constrain the phylogenetic placement of late Paleoproterozoic microfossils and test for the presence of stem- or crown-group eukaryotes during this critical interval. Ultimately, this work has the potential to provide critical insights into the evolutionary tempo and mode of early life, establishing the Gaoshanhe Group as a significant archive for documenting early eukaryotic diversification in the late Paleoproterozoic.