Ciliated protozoans from the Precambrian Doushantuo Formation, Wengan, South China

Abstract Ciliates, a major eukaryotic crown-group lineage with thousands of living species, are poorly represented in the fossil record. Ciliate biomarkers are known from the Precambrian, but only one group, the tintinnids, have an extensive fossil record dating back to the Ordovician. Thus, the occurrence of probable ciliate body fossils in Neoproterozoic rocks confirms their earlier appearance, so far inferred only from molecular sequence data and biomarkers. In this paper, we describe those fossils from the 580 million year old Precambrian Doushantuo phosphates, Guizhou, South China. Three new monospecific genera (100 µm to 200 µm in size) are represented by three-dimensional specimens with exceptionally well-preserved cell bodies including cilia, cytostome and tentacles. Two possess loricas and are referred to the tintinnids. The third has numerous tentacles, an apical cytostome and somatic cilia; it is interpreted as an ancestral early suctorian ciliate. These fossils indicate that the origin and evolutionary differentiation and specialization of ciliates took place before or along with the radiation of other crown-group eukaryotes, including metazoans.