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Quantifying foraminiferal growth with high-resolution X-ray computed tomography: New opportunities in foraminiferal ontogeny, phylogeny, and paleoceanographic applications

¹ Department of Earth and Environmental Sciences, K.U. Leuven, B-3001, Leuven, Belgium
² Department of Subatomic and Radiation Physics, Centre for X-ray Tomography (UGCT), Ghent University, B-9000, Ghent, Belgium
³ Department of Subatomic and Radiation Physics, Centre for X-ray Tomography (UGCT), and Department of Geology and Soil Science, Ghent University, B-9000, Ghent, Belgium

The latest generation of high-resolution X-ray computed tomography (HRXCT), with a submicron resolution, enables for the first time three-dimensional (3D) imaging and biometric quantification of foraminiferal interiors. Here we exemplify the basic possibilities and opportunities of this new technique by means of an analysis on a fossil specimen of Pseudouvigerina sp. from the basal Paleocene of the Brazos River, Texas. The total scan consists of 1200 X-ray radiographs generated during stepwise rotation (0.3°) of the specimen. These radiographs were processed and reconstructed to build cross-sectional images of the object. After 3D rendering of the data, the specimens' chambers could be segmented, showing an exponential ontogenetic growth rate. From the second chamber onward (i.e., after the megalospheric proloculus with a volume of 10⁴ µm³), the size of the chambers steadily increases by a factor of ~1.5. Various other dimensions can also be calculated from the scan, such as the total volume of shell calcite or the size of the foramen. The technological improvements with HRXCT could open up a new era in fundamental biometric-evolutionary research and provide a means of morphologic evaluation of phylogenies based on molecular data. Eventually, the accuracy of paleoceanographic and paleoclimatic reconstructions could also benefit from the possibility of morphological differentiation between cryptic planktic species.

Keywords: foraminifera • X-ray analysis • computed tomography • biometry • phylogeny • pale-oceanography