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This is the published version of a paper presented at 4th International Palaeontological Congress, Mendoza, Argentina.
Citation for the original published paper:
Agić, H., Moczydłowska, M., Canfield, D. (2014)
Cyst and operculum formation in Cambrian-Ordovician galeate acritarchs from Estonia: implications for the algal phylogeny and blooms in the early Paleozoic.
In: 4th International Palaeontological Congress Abstract Volume: The history of life: a view from the Southern Hemisphere (pp. 913-).
N.B. When citing this work, cite the original published paper.
Permanent link to this version:
913
4th INTERNATIONAL PALAEONTOLOGICAL CONGRESS, Mendoza, Argentina. 2014
AASP - The P
alynological Society / P
oster
Unicellular organic-walled microfossils have been recovered from the Cambrian Lükati Formation and the Tremadocian Varangu Formation exposed in northern Estonia. Due to a combination of main morphological and biochemical characters, mainly a) excystment opening, b) processes, c) acetolysis-resistant vesicle wall, microfossils have been interpreted as reproductive cysts of green algae. Both microfossil assemblages reflect the evolutionary patterns through the early Palaeozoic: from the Cambrian radiation of morphologically innovative taxa to increasing in diversity and more disparate Ordovician forms. Combined light transmitted and scanning electron microscopy on the Middle Cambrian to Tremadocian galeate plexus acritarchs Caldariola, Priscogalea and Stelliferidium, revealed exceptionally preserved morphological elements and rare structure among fossil and extant microbiota – an opening with operculum (lid) in reproductive cyst, in addition to lavish vesicle ornamentation and sculpture. Operculum formation model is reconstructed from fossils at different stages of operculum position and attachment. Comparative morphology shows strong similarity of galeates to the reproductive cysts of the extant algae of Dasycladales (Chlorophyta), where the lid covering the cyst opening is determined by an intrinsic lid-forming apparatus during the organism’s reproductive stage. Opercula in Cambro-Ordovician galeate acritarchs and Dasycladales may be considered a homologous character. Unique morphology of the operculum-bearing microbiota would have required a degree of intracellular sophistication for its development, suggesting advanced intracellular machinery present already in the early Palaeozoic phytoplankton. Additionally, a new species of minute, sphaeromorphic and aggregated eukaryotic microfossils is recorded. It possesses a vesicle wall with corrugated sculpture and perforated by nano-scale pores. These minute early Cambrian microfossils have diagnostic characters of prasinophyte algae.
CYST AND OPERCULUM FORMATION IN
CAMBRIAN-ORDOVICIAN GALEATE ACRITARCHS FROM ESTONIA:
IMPLICATIONS FOR THE ALGAL PHYLOGENY
AND BLOOMS IN THE EARLY PALEOZOIC
Heda Agić1, Małgorzata Moczydłowska1 and Donald E. Canfield2
1. Department of Earth Sciences, Uppsala University, Villavägen 16, 752 36 Uppsala, Sweden. heda.agic@geo.uu.se
2. Nordic Centre for Earth Evolution (NordCEE) and Institute of Biology, University of Southern Denmark, DK-5230 Odense, Denmark.
