A WHALE SKELETON-BIVALVE COMMUNITY FROM THE LATE MIOCENE OF CALIFORNIA

We report an apparent fossil whale-fall locality from the late Miocene of Año Nuevo Island, San Mateo County, California. Whale-fall communities were unknown until 20 years ago when a modern community was discovered off the California coast. Since then, a few fossil examples have been described from the Miocene of Japan and the Oligocene of Washington state. Modern and fossil whale-fall communities include many invertebrate taxa, such as Calyptogena, that also occur at hydrothermal vent and cold seeps and are known to harbor chemosymbionts. We describe a partial, but articulated, skeleton of a cetotheriid-grade baleen whale (Cetacea: Mysticeti), recovered from the top of the upper Monterey Formation and below Pleistocene terrace deposits, associated with numerous (>10) silicified fossil Calyptogena? sp. (Mollusca:Bivalvia). These bivalves are small (<1cm in length), occur in clumps, and are predominately preserved in fissures and crevices on the skull, with very few found elsewhere on the skeleton. These bivalves occur in life position and their association with the mysticete skeleton does not appear to be the result of transport and deposition by currents. We interpret this locality as an example of a chemosynthetic whale-fall community based on the preservation of the mysticete skeleton in the same position as modern whale-fall skeletons, the presence of invertebrate taxa whose modern representatives harbor symbionts, and the presence of the bivalves deep within crevices on the skull, a mode of living shared by modern symbiotic mussels. This is the first described fossil whale-fall community from California.