title: Cell differentiation and germ-soma separation in Ediacaran animal embryo-like fossils.
abstract: Phosphorites of the Ediacaran Doushantuo Formation (∼600 million years old) yield spheroidal microfossils with a palintomic cell cleavage pattern. These fossils have been variously interpreted as sulphur-oxidizing bacteria, unicellular protists, mesomycetozoean-like holozoans, green algae akin to Volvox, and blastula embryos of early metazoans or bilaterian animals. However, their complete life cycle is unknown and it is uncertain whether they had a cellularly differentiated ontogenetic stage, making it difficult to test their various phylogenetic interpretations. Here we describe new spheroidal fossils from black phosphorites of the Doushantuo Formation that have been overlooked in previous studies. These fossils represent later developmental stages of previously published blastula-like fossils, and they show evidence for cell differentiation, germ-soma separation, and programmed cell death. Their complex multicellularity is inconsistent with a phylogenetic affinity with bacteria, unicellular protists, or mesomycetozoean-like holozoans. Available evidence also indicates that the Doushantuo fossils are unlikely crown-group animals or volvocine green algae. We conclude that an affinity with cellularly differentiated multicellular eukaryotes, including stem-group animals or algae, is likely but more data are needed to constrain further the exact phylogenetic affinity of the Doushantuo fossils.
authors.affiliation: 1] State Key Laboratory of Palaeobiology and Stratigraphy, and Key Laboratory of Economic Stratigraphy and Palaeogeography, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China [2] College of Earth Science, University of Chinese Academy of Sciences, Beijing 100049, China.
authors.forename: Lei
authors.initials: L
authors.lastname: Chen
authors.affiliation: Department of Geosciences, Virginia Tech, Blacksburg, Virginia 24061, USA.
authors.forename: Shuhai
authors.initials: S
authors.lastname: Xiao
authors.affiliation: 1] State Key Laboratory of Palaeobiology and Stratigraphy, and Key Laboratory of Economic Stratigraphy and Palaeogeography, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China [2] College of Earth Science, University of Chinese Academy of Sciences, Beijing 100049, China.
authors.forename: Ke
authors.initials: K
authors.lastname: Pang
authors.affiliation: State Key Laboratory of Palaeobiology and Stratigraphy, and Key Laboratory of Economic Stratigraphy and Palaeogeography, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China.
authors.forename: Chuanming
authors.initials: C
authors.lastname: Zhou
authors.affiliation: 1] State Key Laboratory of Palaeobiology and Stratigraphy, and Key Laboratory of Economic Stratigraphy and Palaeogeography, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China [2] Department of Geology, Northwest University, Xi'an 710069, China.
authors.forename: Xunlai
authors.initials: X
authors.lastname: Yuan
mesh_terms: D000818:Animals; D017209:Apoptosis; D036703:Blastula / Q000166:cytology; D002454:Cell Differentiation; D002681:China; D000460:Chlorophyta / Q000166:cytology; D004625:Embryo, Nonmammalian / Q000166:cytology*; D005057:Eukaryotic Cells / Q000145:classification / Q000166:cytology; D005580:Fossils; D010802:Phylogeny