2018/04/20 by Zofia Dubicka, Krzysztof Owocki, Michał Gloc · 1 citation
Earth and Planetary Sciences · #Geological and Geochemical Analysis #Geology and Paleoclimatology Research #Paleontology and Stratigraphy of Fossils
paper · doi:10.2113/gsjfr.48.2.142
openalex publication_date 2018/04/20 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/22
Abstract The test structures of Lagenida, Rotaliida, and Miliolida (Foraminifera) are described at an unprecedented scale of resolution. Observations using conventional and field-emission scanning electron microscopy revealed distinct micro- and nanoscale differences in the textural compositions of these three main groups of calcifying foraminifers, consistent with recent molecular phylogenetic reconstructions and a higher-level taxonomic system. The rotaliid test is entirely composed of roughly spherical primary carbonate nanograins, up to 100 nm in diameter, which merge into micrometer-sized irregular aggregates. The miliolid test is made up of two morphologically different primary crystallites. Arbitrarily arranged needle-shaped elements (up to 1 µm in length and 200 nm in width) make up the bulk of the test, including the inside of the wall (porcelain) and mineralized inner surface (intrados) (ca. 100 nm in thickness). Roughly spherical nanograins (up to 50 nm in diameter) form more or less regularly arranged polygons of an outer lamina (extrados), which is ca. 200 nm in thickness. By contrast, the lagenid test texture is characterized by much larger crystals than in other calcifying foraminifers. At moderate magnification, lagenid tests display a fibrous texture composed of fiber bundles (tens of μm in length and several μm in width) that are oriented perpendicular to test surfaces and taper towards the ends when in contact with another lamina. At higher magnification, each bundle constitutes a single calcite crystal with an inner pore extending along the entire length of the crystal/fiber. We measured test hardness using the nanoindentation method. This is the first application of this technique in microfossils. We found that Cretaceous Lagenida tests were more resistant to mechanical stress than Rotaliida tests. These comparative strengths may be linked to internal test microstructure and play a role in determining habitats in which these taxa can live.