An evaluation of morphometrical trends in a population of Woodringina hornerstownensis Olsson, 1960 (Foraminifera) reveals the role of intraspecific variations for paleoceanographical studies

The foraminiferal species Woodringina hornerstownensis is stratigraphically limited between the stages Danian and Selandian and was adapted to inhabit the mixed layer water column. We present a case study based on morphometry of W. hornerstownensis recovered in upper Danian strata (biozone P2) in the Pernambuco-Paraiba Basin at the Poty quarry. The morphometric data, associated with abundance and geochemical indicators, point to (i) an increase in size towards the top of the studied interval, associated with the shallowing-upward trend of the Maria Farinha Formation, and (ii) an increase in size directly related to the increase in abundance. By integrating and incorporating a specific variation of W. hornerstownensis into abundance parameters, we conclude that the shell increase appears to be consistent. Our results suggest that the increase in size responds to environmental optimum conditions for the species W. hornerstownensis. In a broader context, our work demonstrates the usefulness of morphometric indicators and the significance of intraspecific variation when interpreting macroecological patterns. Keywords: planktic foraminifera, paleoceanography, intraspecific variation, upper Danian, South Atlantic Ocean.