Molecular Palaeontology Prospects From Exceptionally Preserved Eocene Brackish‐Water Bivalve <i>Batissa sitakaraensis</i> (Venerida: Corbiculidae) From Hokkaido, Japan

ABSTRACT Unravelling Earth's life history at the molecular level is a long‐standing goal of molecular palaeontology, but the discovery of fossils with preserved ancient biomolecules remains limited. Reports of organic molecules surviving for tens of millions of years are particularly rare. This study investigates the exceptional preservation of a fossilised brackish‐water bivalve, Batissa sitakaraensis (Venerida: Corbiculidae), from the middle Eocene Yubetsu Formation (Urahoro Group, East Hokkaido, Japan), dated to approximately 38 million years ago. Detailed analyses using scanning electron microscopy (SEM) and x‐ray diffraction (XRD) confirmed that the original aragonitic shell microstructure was preserved without significant alteration. Furthermore, the infrared absorption spectra revealed that β ‐chitin, a major component of the periostracum, was retained. Notably, proteinaceous material was detected in a crude extract, and comparisons with the host rock matrix and the closely related extant species B. violacea support the presence of endogenous molecular remnants in the fossil. These findings collectively suggest a unique taphonomic pathway that allowed for the remarkable preservation of both inorganic and organic components in this Eocene brackish‐water bivalve fossil. This fossil represents a promising material for molecular palaeontology, especially in the study of ancient proteins, and offers significant insights into the processes of fossilisation and the mechanisms of molecular preservation.