Discoveries of animal embryos have profoundly improved our understanding of the early evolution of animal development. However, the fossil record of early animal embryos is extremely sparse. Here we present some three-dimensionally (3-D) phosphatized Archaeooides from the basal Cambrian in southern Shaanxi Province, China. The 3-D reconstructions of a number of specimens, aided by high-resolution X-ray tomography, demonstrate that these soft-bodied fossil organisms have a thick cyst characterized by pustule-like ornaments and vesicular structures. Furthermore, a multicellular inner body undergoing palintomic cell division is enclosed by the cyst. The suite of characters, including submillimeter to millimeter scale, a palintomic pattern of cell division, and a complex cyst wall microstructure, corroborate the hypothesis that Archaeooides fossils represent the embryonic remains of animals. More specifically, the structure of the cyst wall bears close comparison to the resting cysts of living invertebrates, allowing us to interpret Archaeooides as a diapause embryonic stage adapted to the temporally and spatially heterogeneous redox conditions that extended from the Ediacaran to the early Cambrian. The global distribution of Archaeooides indicates that these conditions were geographically widespread. Ultimately, Archaeooides provides evidence of the early evolution of this metazoan life history strategy as an adaptation to adverse environmental conditions. Its widespread occurrence in both conventional and exceptional taphonomic windows provides the potential for reconstructing its embryology and, by inference, the developmental evolution of early animals and their body plans.
JOURNAL ARTICLE
Early Cambrian animal diapause embryos revealed by X-ray tomography
Zongjun Yin
Zongjun Yin
1
State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China2
Center for Excellence in Life and Paleoenvironment, Chinese Academy of Sciences, Nanjing 210008, China
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Duoduo Zhao
Duoduo Zhao
1
State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China
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Bing Pan
Bing Pan
1
State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China
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Fangchen Zhao
Fangchen Zhao
1
State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China2
Center for Excellence in Life and Paleoenvironment, Chinese Academy of Sciences, Nanjing 210008, China
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Han Zeng
Han Zeng
1
State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China
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Guoxiang Li
Guoxiang Li
1
State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China2
Center for Excellence in Life and Paleoenvironment, Chinese Academy of Sciences, Nanjing 210008, China
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David J. Bottjer
David J. Bottjer
3
Department of Earth Sciences, University of Southern California, Los Angeles, California 90089, USA
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Maoyan Zhu
Maoyan Zhu
1
State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China2
Center for Excellence in Life and Paleoenvironment, Chinese Academy of Sciences, Nanjing 210008, China4
College of Earth Sciences, University of Chinese Academy of Sciences, Shijingshan, Beijing 100049, China
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Geology (2018)
Published:
February 23, 2018
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Zongjun Yin, Duoduo Zhao, Bing Pan, Fangchen Zhao, Han Zeng, Guoxiang Li, David J. Bottjer, Maoyan Zhu; Early Cambrian animal diapause embryos revealed by X-ray tomography. Geology doi: https://doi.org/10.1130/G40081.1
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