Colonial palynomorphs from the Upper Ordovician of north-eastern Iran: ‘thalli’, coenobial Chlorophyceae (Hydrodictyaceae) or cyanobacteria?

Abstract

This study documents ‘colonial’ palynomorphs from the Upper Ordovician Ghelli Formation of north-eastern Iran. The aggregates of organic-walled microfossils come from the Katian Armoricochitina nigerica–Ancyrochitina merga chitinozoan biozones of this formation. The ‘colonial’ microfossils can be classified as acritarchs and/or cryptospores, but they cannot be attributed to a particular biological group. Some specimens resemble ‘thalli’ of putative spores, such as Grododowon orthogonalis Strother 2017. Other clusters may suggest an affinity to green algal groups, in particular to colonial chlorophyceaen algae, most probably belonging to Hydrodictyaceae. Some specimens also show morphological similarities with cyanobacterial groups. There is so far no evidence to relate these ‘colonial’ palynomorphs to primitive land plants, but we hypothesise that they were possibly produced by ancient green algal lineages with some kind of subaerial existence.

Keywords:

• acritarchs
• cyanobacteria
• embryophytes
• green algae
• spore

Acknowledgements

We thank the three reviewers of our manuscript, Reed Wicander (Mount Pleasant, USA), Paul Strother (Boston, USA) and an anonymous referee, for their valuable comments that greatly improved this paper. We also thank Managing Editor Jim Riding (Nottingham, UK), for the editorial work and useful comments. Navid Navidi-Izad acknowledges the palaeontological team of the Evo-Eco-Paleo unit (Lille University – CNRS) for making his research stay possible. He also acknowledges financial support received from the Iranian Ministry of Science, Research, and Technology (MSRT). Thomas Servais thanks Van Mildert College, University of Durham, for financing a Prowse research fellowship. Hamed Bouzari Nezhad is acknowledged for his invaluable assistance during field work in Iran. This is a contribution to IGCP no. 653, ‘The onset of the Great Ordovician Biodiversification Event’.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Notes on contributors

Navid Navidi-Izad

NAVID NAVIDI-IZAD is currently a PhD student at the Department of Earth Sciences, Kharazmi University, Tehran, Iran, working on the biostratigraphy, palaeoecology, and palaeobiogeography of the Lower Palaeozoic palynomorphs of northern Iran. He received his MSc in stratigraphy and palaeontology in 2013 from Tehran University, Iran. Navid visited the Evo-Eco-Paléo unit of University of Lille, France, for an 8-month sabbatical leave in 2018 and 2019.

Hossein Hashemi

HOSSEIN HASHEMI has been an associate professor in the Department of Geology, Faculty of Earth Sciences, Kharazmi University, Tehran, Iran since 1999. He obtained his MSc degree from Tehran University in 1990, working on Early Permian palynomorphs from the Alborz Ranges, northern Iran. Awarded a PhD scholarship by the Australian government, he continued research on Palaeozoic palynomorphs and received his doctoral degree from The University of Queensland in 1997. He is principally interested in the systematics and stratigraphic applications of Palaeozoic and Mesozoic palynomorphs.

Borja Cascales-Miñana

BORJA CASCALES-MIÑANA After graduating in Spain and post-docs in France and Belgium, Borja Cascales-Miñana joined the CNRS as research fellow in 2017. He works on the early evolution of vascular plants and the Paleozoic floras. He has a special interest in the study of the first terrestrial ecosystems and the great biotic crises of vegetation. His activity involves the use of fossil-based data analysis to elucidate the plant dynamics through time, as well as regular fieldworks for the study of plant macrofossils and spore diversity.

Sylvie Régnier

SYLVIE REGNIER Graduated as a biotechnology technician and started working in the University Hospital Calmette at Lille (France) in the hematology lab (specializing in chemoresistance in Acute Myeloid Leukemia), before joining a private laboratory of soil, water and air analyses. She arrived in the Earth Science Department of the University of Lille in 2006. After training in the palynology laboratories of Lille and Liège (Belgium), she now specializes in palynomorph and microfossil extraction techniques, and currently works on optimizing the methods of palynomorph extraction (improving time and quality). She is also responsible for the SEM platform of the palaeontology research team of the Evo-Eco-Paleo CNRS research unit that she integrated in 2017.

Charles H. Wellman

CHARLES WELLMAN is Professor of Palaeobiology in the Department of Animal and, Plant Sciences of the University of Sheffield, UK. He received a B.Sc. from the University of Southampton in 1987 and a Ph.D. from Cardiff University in 1991 (A NERC CASE award with the Natural History Museum, London). Charles’ Ph.D. research involved a study of early land plant microfossils from Scottish Silurian-Devonian ‘Lower Old Red Sandstone’ deposits. Subsequently Charles’ research has diversified to investigate various aspects of the colonisation of the land, including work on both fossil and living plants, and a consideration of what lived on the land before the land plants.

Thomas Servais

THOMAS SERVAIS is a research director at the French Centre of Scientific Research (CNRS). He was trained as a geologist at the universities of Namur and Liege in Belgium, and received a PhD on Ordovician acritarchs in 1993. After postdoctoral studies in Belgium, Germany and the United Kingdom, Thomas was recruited as a CNRS research associate at the University of Lille in 1997. His research is focused on Lower Palaeozoic microphytoplankton. Thomas is currently vice-chairman of the International Subcommission of Ordovician Stratigraphy (ISOS) and co-leader of the International Geoscience Programme (IGCP) 653 ‘The onset of the Great Ordovician Biodiversification Event’ (2016-2020).