Life was microbial for the majority of Earth's history, but as very few microbial lineages leave a fossil record, the Precambrian evolution of life remains shrouded in mystery. Shelled (testate) amoebae stand out as an exception with rich documented diversity in the Neoproterozoic as vase-shaped microfossils (VSMs). While there is general consensus that most of these can be attributed to the Arcellinida lineage in Amoebozoa, it is still unclear whether they can be used as key fossils for interpretation of early eukaryotic evolution. Here, we present a well-resolved phylogenomic reconstruction based on 250 genes, obtained using single-cell transcriptomic techniques from a representative selection of 19 Arcellinid testate amoeba taxa. The robust phylogenetic framework enables deeper interpretations of evolution in this lineage and demanded an updated classification of the group. Additionally, we performed reconstruction of ancestral morphologies, yielding hypothetical ancestors remarkably similar to existing Neoproterozoic VSMs. We demonstrate that major lineages of testate amoebae were already diversified before the Sturtian glaciation (720 mya), supporting the hypothesis that massive eukaryotic diversification took place in the early Neoproterozoic and congruent with the interpretation that VSM are arcellinid testate amoebae.

Department of Biological Sciences Mississippi State University Starkville MS USA; Department of Biology and Ecology Faculty of Science University of Ostrava Czech Republic

Department of Biological Sciences Mississippi State University Starkville MS USA; Institute for Genomics Biocomputing and Biotechnology Mississippi State University Starkville MS USA

Department of Geophysics Institute of Astronomy Geophysics and Atmospheric Sciences University of São Paulo Brazil

Department of Zoology Institute of Biosciences University of São Paulo Brazil

Department of Zoology Institute of Biosciences University of São Paulo Brazil; Institute of Parasitology Biology Centre Czech Academy of Sciences Branišovská 1160 31 37005 České Budějovice Czech Republic

Laboratory of Soil Biodiversity University of Neuchâtel Rue Emile Argand 11 2000 Neuchâtel Switzerland; Botanical Garden of Neuchâtel Pertuis du Sault 58 2000 Neuchâtel Switzerland

Real Jardín Botánico CSIC Plaza Murillo 2 ES 28014 Madrid Spain; Laboratory of Soil Biodiversity University of Neuchâtel Rue Emile Argand 11 2000 Neuchâtel Switzerland

Curr Biol. 2019 Mar 18;29(6):R212-R215. doi: 10.1016/j.cub.2019.02.003. PubMed

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Phylogenetic reconstruction and evolution of the Rab GTPase gene family in Amoebozoa