Spine-like structures in Paleogene muricate planktonic foraminifera

Pearson, Paul N. ORCID: https://orcid.org/0000-0003-4628-9818, John, Eleanor, Wade, Bridget S., D'haenens, Simon and Lear, Caroline H. ORCID: https://orcid.org/0000-0002-7533-4430 2022. Spine-like structures in Paleogene muricate planktonic foraminifera. Journal of Micropalaeontology 41 (2) , pp. 107-127. 10.5194/jm-41-107-2022

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Abstract

Muricate planktonic foraminifera comprise an extinct clade that was diverse and abundant in the Paleogene oceans and are widely used in palaeoclimate research as geochemical proxy carriers for the upper oceans. Their characteristic wall texture has surface projections called “muricae” formed by upward deflection and mounding of successive layers of the test wall. The group is generally considered to have lacked “true spines”: that is, acicular calcite crystals embedded in and projecting from the test surface such as occur in many modern and some Paleogene groups. Here we present evidence from polished sections, surface wall scanning electron microscope images and test dissections, showing that radially orientated crystalline spine-like structures occur in the centre of muricae in various species of Acarinina and Morozovella and projected from the test wall in life. Their morphology and placement in the wall suggest that they evolved independently of true spines. Nevertheless, they may have served a similar range of functions as spines in modern species, including aiding buoyancy and predation and especially harbouring algal photosymbionts, the function for which we suggest they probably first evolved. Our observations strengthen the analogy between Paleogene mixed-layer-dwelling planktonic foraminifera and their modern spinose counterparts.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Earth and Environmental Sciences
Publisher:	Copernicus Publications
ISSN:	2041-4978
Funders:	NERC
Date of First Compliant Deposit:	20 September 2022
Date of Acceptance:	1 July 2022
Last Modified:	06 Jul 2023 19:14
URI:	https://orca.cardiff.ac.uk/id/eprint/152756

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