DOI: 10.5061/dryad.3bk3j9kqh
title: Size and shape data of Globigerinoidesella fistulosa, Trilobatus sacculifer and intermediate specimens from ODP Site 1115

description: Planktonic foraminifera are extremely well-suited to study evolutionary
 processes in the fossil record due to their high-resolution deposits and
 global distribution. Species are typically conservative in their shell
 morphology with the same geometric shapes appearing repeatedly through
 iterative evolution, but the mechanisms behind the architectural limits on
 foraminiferal shell shape are still not well understood. To understand
 when and how these developmental constraints can be overcome, we study
 morphological change leading up to the origination of the unusually ornate
 species Globigerinoidesella fistulosa. Our results show that the
 origination of G. fistulosa from the Trilobatus sacculifer plexus involved
 an amalgamation of three different heterochronic expressions: addition of
 chambers (hypermorphosis), earlier onset of protuberances
 (pre-displacement), and steeper allometric slope (acceleration) as
 compared to its ancestor. We argue that the protuberances unique to G.
 fistulosa were necessary to sustain a surface-area: volume ratio that
 could host sufficient numbers of photosymbionts. Our work provides a case
 study of the complex combination of processes required to produce unusual
 shell shapes and highlights the importance of developmental processes in
 evolutionary origination. 
description: <em>Study species</em>.—<em>Globigerinoidesella</em>
 <em>fistulosa</em> is a short-ranging morphospecies with a
 distinct stratigraphic range (Fig. 3). Both its origination and extinction are used
 as markers in Neogene planktonic foraminiferal biostratigraphy
 (Wade et al.
 2011). <em>Globigerinoidesella
 fistulosa</em> evolved from the <em>Trilobatus
 sacculifer</em> plexus in the late Pliocene at 3.33 Ma
 (King et al. 2020; Raffi
 et al. 2020) and went
 extinct in the early Pleistocene at 1.88 Ma, marking the Base of Zone PT1a
 (Raffi et al.
 2020)
 (Fig.
 3). The phylogenetic
 relationships are well-constrained, and the two morphospecies <em>T.
 sacculifer </em>sensu stricto (s.s.) and <em>G. fistulosa
 </em>s.s. are morphologically disparate (Poole and Wade 2019), but intermediate specimens bridge the
 morphological evolution (Fig. 2) and remain as common as <em>G. fistulosa
 </em>s.s. throughout the stratigraphic range<em> </em>of
 <em>G. fistulosa </em>(Poole and Wade 2019). <em>Trilobatus sacculifer
 </em>persists throughout the stratigraphic range of <em>G.
 fistulosa </em> and is still alive today (Wade et al. 2011), occupying the mixed-layer in warm tropical
 oceans and harbouring algal photosymbionts (Kucera 2007). Geochemical data indicates that <em>G.
 fistulosa</em> had the same habitat as
 <em>Trilobatus</em> (Poole 2017)<em>.</em>
 <em>Material</em>. —Ocean Drilling Program (ODP) Site 1115 is
 located in the western Woodlark Basin, western Pacific (9º11.382’ S,
 151º34.437’ E) at a water depth of 1149 m (Fig. 4). Site 1115 was chosen primarily because the
 <em>G. fistulosa</em> specimens are abundant and
 well-developed. Eleven late Pliocene samples containing solely
 <em>T. sacculifer</em> plexus, i.e., before the first
 occurrence of <em>G. fistulosa </em>sensu stricto (s.s.), and
 three pooled closely-spaced samples following the speciation (i.e.,
 post-speciation samples) were analysed. Samples were dry sieved at the 250
 μm size fraction and picked for all <em>T. sacculifer
 </em>plexus and <em>G. fistulosa </em>tests, resulting
 in over 900 specimens. Specimens were positioned in umbilical view and
 imaged using a camera mounted on a light microscope. Images were analysed
 using the Image Pro Premier software (version 9.3).
   A
 magnetostratigraphy was previously developed at Site 1115
 (Takahashi et al.
 2001) and provides
 independent age control via the most recent geomagnetic polarity timescale
 (Gradstein et al.
 2020). The integrated
 stratigraphy for Site 1115 by Chuang et al. (2018) unfortunately ends slightly younger than our
 studied interval. We used biostratigraphy (this study) and
 magnetostratigraphy of Takahashi et al. (2001), to determine the age of the samples studied,
 extrapolating back in time from the tuned record of Chuang et al. (2018).   <em>Analysis.</em>—All specimens were analysed for total test area
 and curvature as measured from two-dimensional images
 (Fig.
 5). Test curvature is
 calculated as follows: C =
 (P<sup>2</sup>)/(4*pi*A)<br>
 Here
 <em>P </em>is test perimeter (μm) and <em>A
 </em>is test area (μm<sup>2</sup>). The equation divides
 specimen perimeter length by surface area, as measured from the umbilical
 side. Lengthier perimeters score higher curvature values, and thus
 specimens that are lobate with high numbers of protuberances such as
 <em>G. fistulosa </em>s.s. will have higher curvature values
 than specimens with a more rounded test periphery like <em>T.
 sacculifer </em>s.s.
description: Excel or Google Spreadsheets
description: # Size and shape data of Globigerinoidesella fistulosa, Trilobatus
 sacculifer and intermediate specimens from ODP Site 1115 ## Description of
 the Data and file structure The file titled
 number_of_chambers_per_specimen.xlsx contains the total number of chambers
 per specimen of ten individuals of T. sacculifer and intermediate
 specimens, and 14 specimens of G. fistulosa. Every row contains a single
 specimen. The file titled
 SizeShape_data_sacculifer-fistulosa_individuals.xlsx contains area and
 curvature data as obtained from 2D images. Every row contains a single
 specimen. ## Sharing/access Information Links to other publicly accessible
 locations of the data: none Was data derived from another source? - No If
 yes, list source(s): N/A **Version changes** 19-20 December 2024: added
 sample IDs and ages to the size and shape data of T. sacculifer, G.
 fistulosa and intermediate specimens. These can be found in the file
 titled
 '[SizeShape_data_sacculifer-fistulosa_individuals_with_sample_ID_and_age_updated_2024.xlsx'](https://datadryad.org/stash/downloads/file_stream/3739733 "SizeShape_data_sacculifer-fistulosa_individuals_with_sample_ID_and_age_updated_2024.xlsx")