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Reproductive cyst and operculum formation in the Cambrian-Ordovician galeate-plexus microfossils
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Palaeobiology. (ORIGINS AND EARLY DIVERSIFICATION OF PHOTOSYNTHETIC MICROBIOTA)
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Palaeobiology. (ORIGINS AND EARLY DIVERSIFICATION OF PHOTOSYNTHETIC MICROBIOTA)
University of Southern Denmark .
2016 (English)In: GFF, ISSN 1103-5897, E-ISSN 2000-0863, Vol. 138, no 2, 278-294 p.Article in journal (Refereed) Published
Abstract [en]

Unicellular organic-walled microfossils from the Cambrian-Ordovician transition in Estonia (ca. 490-480 million years ago) exhibit rare characters reflecting their function as reproductive algal cysts. The studied assemblages record the evolutionary history of phytoplankton in the early Paleozoic Era: novel morphologies appearing through the Cambrian and subsequently diversifying in the Ordovician. Well preserved specimens were extracted following a standard palynological method and studied by light transmitted microscopy. The galeate plexus acritarchs Caldariola, Priscogalea and Stelliferidium have revealed exceptionally preserved morphological elements and a rare structure among both fossil and extant protists – an opening with operculum (lid) in reproductive cysts, in addition to lavish vesicle ornamentation and sculpture. Analogous morphology is observed in the living dasycladalean alga Acetabularia (Chlorophyta), which possesses an intrinsic lid-forming apparatus used during organism’s reproductive stage. Based on the observations on the fossil material and studies on the Acetabularia lid-formation, we propose a model of operculum formation in the galeate plexus microorganisms. Due to strong morphological and ecological similarities between galeate fossils and dasycladalean cysts, and the antiquity of this algal order, galeates may be positioned within green algae, more specifically Dasycladales. Unique morphology of the operculum-bearing microbiota would have required a high degree of intracellular complexity for its development, suggesting that advanced intracellular machinery was present already in the early Paleozoic phytoplankton. Additionally, minute prasinophyte microfossils Reticella corrugata  are reported for the first time in the Upper Cambrian strata. 

Place, publisher, year, edition, pages
2016. Vol. 138, no 2, 278-294 p.
Keyword [en]
acritarchs, Baltica, cyst-formation, Dasycladales, Estonia, galeate plexus, microfossils, operculum, Ordovician, palaeobiology
National Category
Geology Botany
Research subject
Earth Science with specialization in Historical Geology and Palaeontology
Identifiers
URN: urn:nbn:se:uu:diva-265207DOI: 10.1080/11035897.2015.1116603ISI: 000379763500001OAI: oai:DiVA.org:uu-265207DiVA: diva2:864105
Projects
Palaeobiology and diversification of Proterozoic-Cambrian photosynthetic eukaryotes
Funder
Swedish Research Council, 621-2012-1669Danish National Research Foundation, DNRF53
Available from: 2015-10-25 Created: 2015-10-25 Last updated: 2017-12-01Bibliographically 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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