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Microfossils Reveal New Biomineralization Styles.
20 June 2013
Calcareous microplankton shells form the dominant components of ancient and modern pelagic sea-floor carbonates are widely used in palaeoenvironmental reconstructions.
Microscopic remains of minute marine plankton are present in their billions in the rocks beneath our feet. However, the small size and fragility of these objects often results in imperfect fossil records, but, very rarely, we find rocks containing unaltered remains that provide windows onto long-gone biology, ecosystems and environments. In a paper just published in Nature Communications, Prof Paul Bown and Dr Jens Wendler (Bremen) report on new biomineral structures of previously unsuspected complexity in the calcite shells of extinct marine algae (dinoflagellates) from Tanzanian sediments that are 92 million year old. These Cretaceous ‘calcisphere’ fossils have previously been considered biomineralogically unremarkable but our new observations show that the true nature of these shells has been masked by recrystallization. Such transformation can completely mask original fabrics and has kept these particular structures hidden from scientists despite a century of research on these fossils. The pristine Tanzanian fossils are constructed from sub-micron-sized, fiber-like, calcite crystallites that are complexly intergrown to form multilayered, weave-like shell walls. The shells also have clear openings (called archeopyles) and corresponding plate-like coverings (called opercula) from which new cells escaped during the reproductive cycle of these algae. Such features demonstrate that these extinct fossils (called pithonellids) are related to living dinoflagellate algae, a link which has long been uncertain. These algae lived in the sunlit upper layers of the ocean and their elaborate shells provided the optimum balance of strength, flexibility and weight needed to give protection but prevent rapid sinking into deeper water.
This work was carried out as part of the Tanzanian Drilling Project
(TDP) which is an international palaeoclimate research programme that aims to
better understand the way Earth’s climate and biosphere has functioned during
times of much warmer climate.