Paleoecology and evolution of Jurassic–Cretaceous corbiculoids from Japan

Corbiculoids are a group of benthic bivalves found in brackish-water environments. Abundant fossil corbiculoids from the Jurassic–Cretaceous strata of Japan are important for interpreting corbiculoid evolution. Most paleontological studies have been concerned with their taxonomy or phylogeny. This study addresses their paleoecology and adaptive strategies to better understand their evolution. Through analyses of fossil assemblages and shell functional morphology, representative corbiculoid species (i.e., Eomiodon lunulatus, E. vulgaris, Costocyrena otsukai, C. radiatostriata, Crenotrapezium kurumense, C. kitakamiense, Myrene tetoriensis, Isodomella shiroiensis, Filosina jusanhamensis, Tetoria sanchuensis, T. yokoyamai, Hayamina naumanni, and H. matsukawai) are interpreted to have been rapid but shallow burrowers, and suspension feeders. This paleoecological interpretation indicates that corbiculoid species were adapted to brackish-water environments. However, to maintain an ecological niche in the environment, organisms must be able to respond to environmental instability. Thus, temporal changes in the stratigraphic and spatial distributions of 23 well-studied corbiculoid species during the Jurassic and Cretaceous were examined. As a result, it is clarified that some corbiculoid species avoided relatively small environmental changes by migration to refugia. On the basis of the occurrence pattern of the corbiculoid species, it is also argued that corbiculoids are polyphyletic, with multiple speciations enabling them to persist from the Jurassic to recent.