Miocene whale-fall community from Hokkaido, northern Japan

Whale bones have been found in two large concretions in the uppermost part of the lower middle Miocene Chikubetsu Formation, northwestern Hokkaido, Japan. The bone surfaces are coated in pyrite, and some of the most exterior bone portions and associated bone chips are extensively bored by an unknown organism, possibly microbial. Closely associated with the whale bones is a fossil mollusc assemblage including the mytilid Adipicola chikubetsuensis (Amano), Solemya sp., Vesicomya ? sp. and Calyptogena sp. and the gastropod Provanna sp. These molluscs represent a chemosynthetic community dependent on the decaying whale bone-lipids for nutrition, and the mytilids, vesicomyids and solemyids almost certainly had symbiotic chemoautotrophic bacteria. Since the Oligocene, small mussels, such as Adipicola or Idas, and vesicomyid bivalves have been common elements of whale-fall communities in the Pacific; Provanna similarly since at least the Miocene. However, there are some important differences between modern and fossil whale-fall communities, not least that there appear to be no shared species.