First computer-assisted 3D-reconstruction of calpionellid tests (Protozoa incertae sedis) and corresponding section restoration

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Calpionellids are widespread protozoans of Late Jurassic-Early Cretaceous age, typically found in Tethyan pelagic domains and related paleobiogeographic provinces. Their abundance and rapid evolution make them excellent biochronological markers as they are considered by the Berriasian Working Group of the ICS's International Subcommission on Cretaceous Stratigraphy as primary tools for fixing a GSSP to the base of the Berriasian stage (Jurassic-Cretaceous boundary). Regarding the calpionellid entire morphology studies, attempts of their chemical extraction from carbonated matrix are very scarce and, therefore, available 3-D morphologies are very limited. Hence, these microfossils are mostly studied in thin sections where they are randomly cut, leading to apparent variations among representatives of an individual taxon. Therefore, their taxonomy, phylogeny and related biozonations are still subject to divergent interpretations. This work proposes a first Computer-Assisted method for 3D-reconstruction of calpionellid loricae based on published axial sections. It also allows the simulation of all possible random cuts and to visualize corresponding apparent sections. Parametric 3D designs and restored sections can be defined (and stored) in Cartesian coordinate systems that respect the natural proportions of the studied tests. This leads to a more objective systematic paleontology of calpionellid section, a preliminary guide towards updating calpionellid phyletic relationships and biozonation schemes. Beyond calpionellids, our methodology may generate further ideas and alternative digital tools for micropaleontologists and paleontologists working on thin sections, leading to improvements in fossil determinations and taxonomical studies. • New Computer-aided methodology for 3D reconstruction of calpionellid tests • Simulation of calpionellid sections • This helps: 1) approaching a more objective systematic paleontology of calpionellid sections; 2) updating biostratigraphy and phylogeny • The proposed methodology may generate further ideas for micropaleontologists to improve some fossil section taxonomical studies.