Internal pore measurements on macroperforate planktonic Foraminifera as an alternative morphometric approach

Abstract

Because of the lack of genetic control on extinct species, the morphologic approach remains the only way of identifying fossil Foraminifera. In addition to comparative description of gross shell morphology, morphometry became more important in recent years and was extended to encompass the ultrastructure of the shells. In particular, some studies focused on porosity, as determined by the pore diameters plotted against the number of pores per given surface. However, taking into account the poor preservation and recrystallization, which often affects and characterizes fossil specimens, and/or the deficiencies connected to the interpretation of scanning electron microscope images, pore measurements are often distorted, limited in number and lacking precision, and thus unreliable. We demonstrate that, by measuring the pores from inside the shell and individually, it is possible to obtain numerous and precise data either on an individual basis or for statistical purposes. This study also suggests that in the Early Miocene Globigerinoides, which is generally strongly susceptible for dissolution, the dissolution proceeds from the external towards the internal side of the shell.

Searching for Function: Reconstructing Adaptive Niche Changes Using Geochemical and Morphological Data in Planktonic Foraminifera

“…Other functional traits such as spines are not readily preserved in situ and require SEM images to identify. However, more complex morphological traits that are more tightly related to biogeochemical function (such as pore density) can now be easily measured through technological advances (Bé, 1968;Constandache et al, 2013;Burke et al, 2018). While gross morphology has been hypothesized to control buoyancy (Caromel et al, 2014), mathematical models suggest any potential relationship is weak at best (Caromel et al, 2017) and such features are variable even within a constant laboratory environment (Davis et al, 2020).…”

“…Some traits have obvious function such as spines for feeding (Hemleben et al, 1991) or the presence of symbionts (Bé et al, 1977(Bé et al, , 1981(Bé et al, , 1982Takagi et al, 2019). Recent studies, building on previous hypotheses, have shown that pores on foraminifera tests may be functionally linked to gas exchange (Bé, 1968;Baumfalk et al, 1987;Burke et al, 2018) but are only measured reliably from the inside of the test requiring scanning electron microscope (SEM) images or micro-CT scanning (Constandache et al, 2013;Burke et al, 2018). In contrast, traits such as test shape and size must have a function, but what those functions are remain highly debated (Renaud and Schmidt, 2003;Caromel et al, 2014;Burke and Hull, 2017).…”

The Influence of Geochemical Variation Among Globigerinoides ruber Individuals on Paleoceanographic Reconstructions

“…We suggest that future morphological studies should focus on final chamber traits as well as investigating morphological differences in the 3D space using μ-CT scanning. Furthermore, we also suggest that future studies measure traits that have a known functional role and can be linked to the environment such as pore size which is linked to gas exchange (Bé, 1968;Burke et al, 2018;Constandache et al, 2013;Kearns et al, 2021).…”

Factors influencing test porosity in planktonic foraminifera

“…2). We quantified porosity from the inner wall of the penultimate chamber in order to avoid known irregularities in the porosity of the final chambers (Bé et al, 1980;Constandache et al, 2013). In Orbulina universa, the only exception, we measured the final chamber, as preceding chambers are typically dissolved in sedimentary remains of this species.…”