DOI: 10.5061/dryad.cjsxksnbm
title: Morphometric data of the late middle Eocene to early Oligocene (~40 - 31 Ma) Coccolithophore Reticulofenestra (Order Isochrysidales)

description: The first size reduction (FSR) in the
 Reticulofenestra-Gephyrocapsa-Emiliania (RGE) lineage (Order
 Isochrysidales) which occurred in the early Oligocene (~ 32 Ma), is of
 great significance for understanding the lilliput effect that has affected
 the coccolithophore communities from late Eocene to this day. We conducted
 a morphologic analysis on the coccoliths of Reticulofenestra species that
 lived during the late middle Eocene to early Oligocene (~40-31 Ma), using
 marine sediments from the South Atlantic Ocean. Our data show increasing
 size and decreasing abundance of the large species during the late Eocene,
 leading to their disappearance at the FSR, and a concurrent decrease in
 the size variability of the small-medium-sized coccoliths whose diameter
 of the central opening had become very reduced. Although the cosmopolitan
 late Paleogene through Neogene size decrease in coccolithophores has been
 linked to the concomitant long-term decline in global pCO2, we suggest
 here that the FSR was the result of environmental destabilization caused
 by the expansion of eutrophic environments following the late Eocene
 establishment of overturning circulation associated with ice build-up on
 Antarctica. This study also leads us to propose a hypothetical model that
 links coccolith morphology of species of the RGE lineage and trophic
 resources in the upper ocean: the small- to medium-sized, r-selected
 coccolithophores with smaller coccolith central opening live in
 nutrient-rich waters where they rely mostly on photosynthesis and little
 on mixotrophy; whereas the larger, K-selected species with larger
 coccolith central opening live in oligotrophic waters where they are more
 dependent on mixotrophy.
description: Morphometric measurements were
 performed by randomly taking photographs in bright field of 10 to 15
 fields of view per smear slide at 1000x magnification. A field of view
 typically contained 5 to 10 <em>Reticulofenestra</em>
 placoliths. For each sample, one hundred (100) specimens were measured. To
 avoid distortion caused by different orientations of the coccoliths as
 seen in light microscopy, only specimens horizontally oriented with the
 microscope stage were measured.<br>Measurements were conducted
 manually using the biometric analysis software Fiji version 1.52 P by
 dragging ellipses over the contours of each placolith in order to measure
 its length and width. The long and short diameters of the central opening
 were likewise measured. Our procedure has resulted in a database of 6400
 measurements for the whole study.<br>We undertook a morphometric
 analysis with the double objective of quantifying the morphological
 features of the placoliths at any stratigraphic level and analyzing their
 change through time. Three characters yield meaningful biological and
 physiological information: 1. Length of coccolith.<br>2. Central
 opening/coccolith length ratio:<br>Length ratio=  (length of the
 central opening/length of the distal shild)*100%.<br>3. Circularity
 of coccolith:<br>Circularity = width of coccolith/length of
 coccolith.<br>Higher circularity means a more circular shape, while
 lower circularity means a more elliptical shape of
 coccoliths. 
description: This file includes the raw data and supplementary descriptions
 that required in the research. The supplementary material includes 1.
 coccolith assemblage, 2. data reproducibility evaluation, 3 estimated cell
 and coccosphere sizes that were mentioned in the manuscript and 4. our
 biostratigraphic interpretation.<br>In the data file, we delineate
 coccolith morphology by two major structures, the distal shield and the
 central opening. Then the length and width of both are given in
 microns.<br>One hundred specimens are measured in each sample, in
 which the sample IDs are present in the first specimens. The ages are
 estimated based on our biostratigraphic interpretation, which is
 introduced in the supplementary text.