A new species of small acritarch with a porous wall structure from the early Cambrian of Estonia and implications for the fossil record of eukaryotic picoplankton

Abstract

The Proterozoic–Phanerozoic transition recorded a general trend of decrease in phytoplankton cell size, in contrast to the earlier and much larger Ediacaran acritarchs. Particularly minute, unornamented but sculptured organic-walled microfossils have been recovered from the lower Cambrian Lükati Formation in northern Estonia. The lack of any significant thermal alteration in this formation allowed for excellent preservation of fine microstructures on these microfossils. Among the rich palynomorph assemblages in the Lükati Formation, a new species of tiny, spheroidal eukaryotic microfossil is recorded: Reticella corrugata gen. et sp. nov. It is characterised by a corrugated and flexible vesicle wall that is densely perforated by nano-scale pores. Despite its unique morphology, the new species shares diagnostic characters with fossil and extant prasinophyte algae. Reticella corrugata is among the smallest microfossils with typical eukaryotic morphology (conspicuous wall sculpture) and contributes to the diversity of the size class of small acritarchs. Size, abundance, inferred prasinophyte affinity and eukaryotic wall sculpture make this new taxon a likely member of the early eukaryotic picoplankton.

Keywords:

• Cambrian
• Estonia
• organic-walled microfossils
• picoplankton
• prasinophytes
• small acritarchs

Acknowledgements

This paper benefitted greatly from constructive feedback by M. Moczydłowska and S. Willman (Uppsala University). I am also grateful to R. Wicander (Central Michigan University) and an anonymous reviewer for their helpful reviews and comments, as well as to the editor J.B. Riding (British Geological Survey) for his suggestions and rapid correspondence.

Disclosure statement

No potential conflict of interest was reported by the author.

Additional information

Funding

The presented work is a part of the author's PhD project and was funded by the Swedish Research Council (VR), grant no. 621-2012-1669.

Notes on contributors

Heda Agić

HEDA AGIĆ is a final-year graduate student at Uppsala University, Sweden. She graduated in Earth Science from University College London, UK and received MSci in Palaeobiology from the same institution in 2011. Her PhD project focuses on studying characters and ultrastructure of Proterozoic and early Paleozoic organic-walled microfossil assemblages from China, Estonia, Norway, and Sweden with aims of better understanding their biological affinities.