Micro-CT morphometric insights into the ecology and taphonomy of triserial planktic foraminifera

Triserial planktic foraminifera recur across the Late Cretaceous-Cenozoic fossil record and have been frequently linked to environmental instability and opportunistic ecological strategies. The 3D test architecture of triserial forms and how it may functionally from other coeval morphologies remains poorly quantified. This study applies micro-CT derived 3D morphometrics to compare common Late Cretaceous (Maastrichtian) planktic morphogroups, and triserial Guembelitria , Jenkinsina , and Neogallitellia spanning the Cretaceous, Paleogene and Recent. The analysed triserial genera exhibit higher size-normalized external test surface area to volume ratios (SA:V s,t > 0.2) and lower net buoyant masses than the analysed Cretaceous morphotypes, characteristics consistent with enhanced suspension efficiency and their inferred surface to shallow mixed-layer habitats. In contrast, biserial and trochospiral taxa display greater volumetric displacement and higher net buoyant masses. These characteristics quantitatively distinguish the test architecture of the analysed triserial forms, and provide a functional basis for their ecological distribution. Taphonomically, high post-mortem total surface area (external and internal chamber wall) to test volume ratios (SA total / V s > 0.4) and low robustness index (RI, a proposed measure of carbonate volume supported per unit surface area) suggest greater susceptibility of triserial forms to dissolution and fragmentation. This case study demonstrates the potential of micro-CT derived 3D test architecture for investigating the functional, ecological and taphonomic significance of microfossil morphology.