Phosphatized spherical microfossils from the Silurian (Motol Formation, Sheinwoodian, Wenlock) of the Barrandian area, Czech Republic.

 

Authors: Cholevová V, Mergl M

Published in: Bulletin of Geosciences, volume 101, issue 2; pages: 275 - 288; Received 10 October 2025; Accepted in revised form 3 March 2026; Online 28 June 2026

Keywords: Sheinwoodian, Silurian, phosphatization, Barrandian, algae, problematic microfossils,

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Abstract

Two phosphatized spherical fossils (approximately 2.5 mm in diameters) observed in limestone of Silurian age (Sheinwoodian, Wenlock) in Central Bohemia, Czech Republic, likely represent phosphatized remains of original organic object. Specimen A exhibits a suggested cellular pattern within a smooth external membrane. The phosphatization of the cell walls, polyhedral and hexagonal outline of the cells, phosphatization of the shrunken protoplast inside the cells, and the differentiation of central and peripheral cell layers presumably indicate the algal affinity of the fossil. Specimen B is larger and lacks the distinct cellular pattern. Below the external smooth membrane, columns of botryoid microcrystals are developed around radially arranged fibres. The central part of Specimen B is formed by a plexus of irregularly spaced fibres with aggregated microcrystalline coatings. A poorly defined break lies between the central region and the peripheral layer. This body is interpreted as a simply structured biological object affected by decay processes and simultaneous phosphatization. The taxonomic affinity of Specimen B is uncertain. It could be an animal egg with the phosphatized outer membrane (chorion). Although very rare in the locality, both spherical fossils indicate the similar taphonomic processes and the unique preservation in the Silurian. So far, a similar preservation was so far known only in the Ediacaran and the lower Cambrian of South China, Siberia, and north-western Canada.

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