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Reproductive cyst and operculum formation in the Cambrian-Ordovician galeate-plexus microfossils
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Paleobiologi. (ORIGINS AND EARLY DIVERSIFICATION OF PHOTOSYNTHETIC MICROBIOTA)
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Paleobiologi. (ORIGINS AND EARLY DIVERSIFICATION OF PHOTOSYNTHETIC MICROBIOTA)
University of Southern Denmark .
2016 (Engelska)Ingår i: GFF, ISSN 1103-5897, E-ISSN 2000-0863, Vol. 138, nr 2, s. 278-294Artikel i tidskrift (Refereegranskat) 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. 

Ort, förlag, år, upplaga, sidor
2016. Vol. 138, nr 2, s. 278-294
Nyckelord [en]
acritarchs, Baltica, cyst-formation, Dasycladales, Estonia, galeate plexus, microfossils, operculum, Ordovician, palaeobiology
Nationell ämneskategori
Geologi Botanik
Forskningsämne
Geovetenskap med inriktning mot historisk geologi och paleontologi
Identifikatorer
URN: urn:nbn:se:uu:diva-265207DOI: 10.1080/11035897.2015.1116603ISI: 000379763500001OAI: oai:DiVA.org:uu-265207DiVA, id: diva2:864105
Projekt
Palaeobiology and diversification of Proterozoic-Cambrian photosynthetic eukaryotes
Forskningsfinansiär
Vetenskapsrådet, 621-2012-1669Danmarks Grundforskningsfond, DNRF53Tillgänglig från: 2015-10-25 Skapad: 2015-10-25 Senast uppdaterad: 2017-12-01Bibliografiskt granskad
Ingår i avhandling
1. Palaeobiology and diversification of Proterozoic-Cambrian photosynthetic eukaryotes
Öppna denna publikation i ny flik eller fönster >>Palaeobiology and diversification of Proterozoic-Cambrian photosynthetic eukaryotes
2015 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
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.

Ort, förlag, år, upplaga, sidor
Uppsala: Acta Universitatis Upsaliensis, 2015. s. 47
Serie
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1308
Nyckelord
microfossils, eukaryotes, Mesoproterozoic, Neoproterozoic, Cambrian, Ordovician, palaeobiology, biostratigraphy, phylogeny, China, Estonia, Siberian Platform, prasinophytes, microstructure, Raman spectroscopy
Nationell ämneskategori
Geologi
Forskningsämne
Geovetenskap med inriktning mot historisk geologi och paleontologi
Identifikatorer
urn:nbn:se:uu:diva-265229 (URN)978-91-554-9389-9 (ISBN)
Disputation
2015-12-11, Hambergsalen, Geocentrum, Villavägen 16, 752 36, Uppsala, 10:15 (Engelska)
Opponent
Handledare
Projekt
Palaeobiology and diversification of Proterozoic-Cambrian photosynthetic eukaryotes
Forskningsfinansiär
Vetenskapsrådet, 621-2009-4445
Tillgänglig från: 2015-11-19 Skapad: 2015-10-26 Senast uppdaterad: 2016-01-13

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