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Affnity, life cycle, and intracellular complexity of organic-walled microfossils from the Mesoproterozoic of Shanxi, China
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Palaeobiology. (Palaeobiology)
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Palaeobiology.
Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences.
2015 (English)In: Journal of Paleontology, ISSN 0022-3360, E-ISSN 1937-2337, Vol. 89, no 1, 28-50 p.Article in journal (Refereed) Published
Abstract [en]

Light microscope and scanning electron microscope observations on new material of unicellularmicrofossils Dictyosphaera macroreticulata and Shuiyousphaeridium macroreticulatum, from the MesoproterozoicRuyang Group in China, provide insights into the microorganisms’ biological affinity, life cycle and cellularcomplexity. Gigantosphaeridium fibratum n. gen. et sp., is described and is one of the largest Mesoproterozoicmicrofossils recorded. Phenotypic characters of vesicle ornamentation and excystment structures, properties ofresistance and cell wall structure in Dictyosphaera and Shuiyousphaeridium are all diagnostic of microalgalcysts. The wide size ranges of the various morphotypes indicate growth phases compatible with the development ofreproductive cysts. Conspecific biologically, each morphotype represents an asexual (resting cyst) or sexual (zygotic cyst)stage in the life cycle, respectively. We reconstruct this hypothetical life cycle and infer that the organism demonstrates areproductive strategy of alternation of heteromorphic generations. Similarly in Gigantosphaeridium, a metabolicallyexpensive vesicle with processes suggests its protective role as a zygotic cyst. In combination with all these charactersand from the resemblance to extant green algae, we propose the placement of these ancient microorganisms in the stemgroup of Chloroplastida (Viridiplantae). A cell wall composed of primary and secondary layers in Dictyosphaera andShuiyouisphaeridium required a high cellular complexity for their synthesis and the presence of an endomembranesystem and the Golgi apparatus. The plastid was also present, accepting the organism was photosynthetic. The biotareveals a high degree of morphological and cell structural complexity, and provides an insight into ongoing eukaryoticevolution and the development of complex life cycles with sexual reproduction by 1200Ma.

Place, publisher, year, edition, pages
Cambridge Journals , 2015. Vol. 89, no 1, 28-50 p.
Keyword [en]
organic-walled microfossils; early eukaryotes; Mesoproterozoic; Dictyosphaera; Shuiyousphaeridium; algae; evolution; intracellular complexity
National Category
Geology
Research subject
Earth Science with specialization in Historical Geology and Palaeontology; Biology with specialization in Systematics
Identifiers
URN: urn:nbn:se:uu:diva-247264DOI: 10.1017/jpa.2014.4ISI: 000351478500003OAI: oai:DiVA.org:uu-247264DiVA: diva2:795472
Funder
Swedish Research Council, 621-2009-4445
Available from: 2015-03-16 Created: 2015-03-16 Last updated: 2017-12-04Bibliographically approved
In thesis
1. Palaeobiology and diversification of Proterozoic-Cambrian photosynthetic eukaryotes
Open this publication in new window or tab >>Palaeobiology and diversification of Proterozoic-Cambrian photosynthetic eukaryotes
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

One of the most important events in the history of life is the evolution of the complex, eukaryotic cell. The eukaryotes are complex organisms with membrane-bound intracellular structures, and they include a variety of both single-celled and multicellular organisms: plants, animals, fungi and various protists. The evolutionary origin of this group may be studied by direct evidence of past life: fossils. The oldest traces of eukaryotes have appeared by 2.4 billion years ago (Ga), and have additionally diversified in the period around 1.8 Ga. The Mesoproterozoic Era (1.6-1 Ga) is characterised by the first evidence of the appearance complex unicellular microfossils, as well as innovative morphologies, and the evolution of sexual reproduction and multicellularity. For a better understanding of the early eukaryotic evolution and diversification patterns, a part of this thesis has focused on the microfossil records from various time periods and geographic locations. Examination of microfossil morphology, cell wall microstructure and biochemical properties, reflect their intracellular complexity and function, and allow reconstructions of their life cycle, as well as observing the evolutionary pattern of change from Mesoproterozoic, to Cambrian-Ordovician transition. Several case studies included assemblages deriving from Mesoproterozoic, Neoproterozoic and early Paleozoic time intervals that show disparate morphotypes and innovative features indicative of algal clades. The Mesoproterozoic Ruyang Group in northern China has yielded a diverse microfossil assemblage that provides important clues about the diversification of different eukaryotic groups. Furthermore these microfossils contributed an additional evidence for the emergence of the crown group Eukarya by 1.7-1.4 Ga. In another part of this thesis, examination of wall microstructure and chemical properties via Raman spectroscopy has been used to assess the biological affinities of various Neoproterozoic problematic carbonaceous compression fossils. Studies on the early Phanerozoic (c. 545-485 Ma) assemblages from Estonia reconstructed patterns of the early radiations of phytoplankton and its evolutionary innovations. A continuing theme in this thesis has been using a combination of evidence of microfossils’ fine-scale morphology, ecology and chemical properties to determine their function in life, in addition to their systematic position.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2015. 47 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1308
Keyword
microfossils, eukaryotes, Mesoproterozoic, Neoproterozoic, Cambrian, Ordovician, palaeobiology, biostratigraphy, phylogeny, China, Estonia, Siberian Platform, prasinophytes, microstructure, Raman spectroscopy
National Category
Geology
Research subject
Earth Science with specialization in Historical Geology and Palaeontology
Identifiers
urn:nbn:se:uu:diva-265229 (URN)978-91-554-9389-9 (ISBN)
Public defence
2015-12-11, Hambergsalen, Geocentrum, Villavägen 16, 752 36, Uppsala, 10:15 (English)
Opponent
Supervisors
Projects
Palaeobiology and diversification of Proterozoic-Cambrian photosynthetic eukaryotes
Funder
Swedish Research Council, 621-2009-4445
Available from: 2015-11-19 Created: 2015-10-26 Last updated: 2016-01-13

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