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Xiao S, Muscente AD, Chen L, Zhou C, Schiffbauer JD, Wood AD, Polys NF, Yuan X. The Weng'an biota and the Ediacaran radiation of multicellular eukaryotes. Natl Sci Rev 2014. [DOI: 10.1093/nsr/nwu061] [Citation(s) in RCA: 97] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Abstract
The rise of multicellularity represents a major evolutionary transition and it occurred independently in multiple eukaryote clades. Although simple multicellular organisms may have evolved in the Mesoproterozoic Era or even earlier, complex multicellular eukaryotes began to diversify only in the Ediacaran Period, just before the Cambrian explosion. Thus, the Ediacaran fossil record can provide key paleontological evidence about the early radiation of multicellular eukaryotes that ultimately culminated in the Cambrian explosion. The Ediacaran Weng'an biota in South China hosts exceptionally preserved eukaryote fossils, including various acanthomorphic acritarchs, pseudoparenchymatous thalli, tubular microfossils, and spheroidal fossils such as Megasphaera, Helicoforamina, Spiralicellula, and Caveasphaera. Many of these fossils have been interpreted as multicellular eukaryotes, although alternative interpretations have also been proposed. In this review, we critically examine these various interpretations, focusing particularly on Megasphaera, which has been variously interpreted as a sulfur-oxidizing bacterium, a unicellular protist, a mesomycetozoean-like holozoan, a volvocine green alga, a stem-group animal, or a crown-group animal. We conclude that Megasphaera is a multicellular eukaryote with evidence for cell-to-cell adhesion, a flexible membrane unconstrained by a rigid cell wall, spatial cellular differentiation, germ–soma separation, and programmed cell death. These features are inconsistent with the bacterium, unicellular protist, and mesomycetozoean-like holozoan interpretations. Thus, the surviving hypotheses, particularly the stem-group animal and algal interpretations, should be further tested with additional evidence. The Weng'an biota also hosts cellularly differentiated pseudoparenchymatous thalli with specialized reproductive structures indicative of an affinity with florideophyte red algae. The other Weng'an fossils reviewed here may also be multicellular eukaryotes, although direct cellular evidence is lacking in some and phylogenetic affinities are poorly constrained in others. The Weng'an biota offers many research opportunities to resolve the life histories and phylogenetic diversity of early multicellular eukaryotes and to illuminate the evolutionary prelude to the Cambrian explosion.
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Affiliation(s)
- Shuhai Xiao
- Department of Geosciences, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA
| | - A. D. Muscente
- Department of Geosciences, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA
| | - Lei Chen
- State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Paleontology, Chinese Academy of Sciences, Nanjing 210008, China
- College of Earth Science, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Chuanming Zhou
- Key Laboratory of Economic Stratigraphy and Palaeogeography, Nanjing Institute of Geology and Paleontology, Chinese Academy of Sciences, Nanjing 210008, China
| | - James D. Schiffbauer
- Department of Geological Sciences, University of Missouri, Columbia, MO 65211, USA
| | - Andrew D. Wood
- Advanced Research Computing, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA
| | - Nicholas F. Polys
- Advanced Research Computing, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA
| | - Xunlai Yuan
- State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Paleontology, Chinese Academy of Sciences, Nanjing 210008, China
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