Encrustation patterns on post-extinction early Famennian (Late Devonian) brachiopods from Russia

Abstract

A study of patterns of episkeletobiont encrustation on the shells of two early Famennian brachiopods, Cyrtospirifer zadonicus and Ripidiorhynchus huotinus from Russia, revealed assemblages comprising seven skeletonised encruster taxa. The assemblages are dominated by spirorbiform microconchids, followed by cornulitids. Features such as shell malformations, frequent encruster growth towards the commissure of the shells, and encruster distribution in the areas adjacent to zones of possible water intake by the brachiopods indicate that these may have been colonised syn vivo. The lack of differences in encruster abundance between the two valves in C. zadonicus indicates that this species may have lived with both valves inclined at a high angle to the substrate. The significantly higher abundance of episkeletobionts on the brachial valves of R. huotinus may indicate that shells of this species were oriented with the brachial valve at a lower angle to the substrate, providing sheltered sites for coelobiotic larvae. Compared with pre-Famennian brachiopod-hosted encruster communities, this early Famennian community is impoverished in species richness and is dominated by microconchids. It is proposed that the epibionts witnessed a regression-related Frasnian–Famennian extinction event. During the recovery interval, opportunistic microconchids may have been among the first encrusters to colonise the pioneering brachiopods.

Keywords:

• encrusters
• brachiopods
• Devonian
• paleoecology
• mass extinction

Acknowledgements

The first author thanks his friends Elena Sokiran (VNIGRI, Saint Petersburg, Russia), who led the field trip to the Central Devonian Field, and Wojtek Krawczyński (Faculty of Earth Sciences, Sosnowiec, Poland), who made the brachiopods available for study and took some of the photographs. We are also indebted to Piotr Kukliński and Piotr Bałazy (Institute of Oceanology, Sopot, Poland), who helped with statistical analyses. Mark Wilson (College of Wooster, OH, USA), Olev Vinn (University of Tartu, Estonia), Paul Taylor (Natural History Museum, London, UK) and Dave Bond (University of Leeds, UK) are acknowledged for providing important publications. Alexandru Tomescu (Humboldt State University, Arcata, CA, USA) kindly improved the language, which is greatly appreciated. This work was supported by the University of Silesia grant BW-43/2002. The manuscript much benefited from the constructive comments, useful remarks and further linguistic corrections provided by two journal referees.

Notes

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Additional information

Notes on contributors

Tomasz Borszcz

1