Multicellularity is a prerequisite for eukaryotes to acquire organismal complexity and large size, yet when eukaryotes first evolved this innovation in their deep evolutionary history is still poorly understood. Early fossil records claimed to be multicellular eukaryotes include various macroscopic and microfossils from Mesoproterozoic and Paleoproterozoic sediments. However, most of them cannot be unambiguously identified as such due to their simple morphology and lack of cellular structure, especially those of Paleoproterozoic records. These include filaments of Qingshania magnifica, initially described from thin sections of shales from late Paleoproterozoic Chuanlinggou Formation (1.65-16.4 Ga) in North China, and interpreted to be primitive green algae (Yan, 1989). However, such interpretation was obscured by poorly illustrated images. Here we document abundant Q. magnifica isolated from shales of Chuanlinggou Fm. by acid maceration and combined techniques of TLM, SEM, Raman and Infrared spectroscopies. The fossils consist of large uniseriate, unbranched filaments with cell diameters up to 194 μm, and show a certain degree of morphological variability. The new finding of intracellular spheroidal structures probably representing spores occurred in some cells, adds another layer of biological complexity. The combination of these features permits the interpretation of these large filaments to be eukaryotic, based on comparisons with extant organisms. The occurrence of multicellular eukaryotes in Paleoproterozoic rocks not much younger than those containing the oldest unambiguous evidence of eukaryotes as a whole supports the hypothesis that simple multicellularity arose early in eukaryotic history, as much as a billion years before complex multicellular organisms diversified in the oceans.

eukaryote,multicellularity,microfossil,Paleoproterozoic