Through-water and underwater photogrammetry for fossil exposure survey in shallow waters

Subaqueous fossiliferous outcrops constitute valuable yet poorly documented paleontological archives, particularly in fluvial environments where accessibility, hydrodynamic reworking, and rapid surface degradation hinder systematic investigation. This study introduces an application of through-water (multimedia) and underwater photogrammetry for the in situ documentation of fossil exposures in optically shallow water (OSW) settings. The approach is applied to a permanently submerged fossiliferous pavement of the Permian Irati Formation exposed on the riverbed of the Passa Cinco River, southeastern Brazil, which preserves exceptionally well-preserved remains of the aquatic reptile Mesosaurus . Drone-based through-water photogrammetry was used to generate high-resolution orthophotos and refraction-corrected digital elevation models at the outcrop scale, enabling detailed spatial mapping of fossil occurrences and geological features. In parallel, close-range underwater photogrammetry acquired through a wading-based workflow provided high-resolution three-dimensional reconstructions of selected specimens, preserving fine-scale morphological and taphonomic attributes. The results demonstrate that the combined workflow enables qualitative and semi-quantitative, non-invasive paleontological investigations in shallow aquatic environments and highlights the potential of integrated photogrammetry for the long-term conservation and reproducibility of submerged fossil records. Furthermore, the proposed workflow enabled effective taphonomic analysis and digital preservation of fragile and dynamically exposed fossiliferous surfaces. All orthophoto datasets and dense point cloud data generated in this study are openly available in a public repository, ensuring data accessibility, reproducibility, and long-term reuse.