oa Steroidal Composition of Fossil Whale Bone and Marine Mammal Bones (Desmostylia) from the Oligocene of Hokkaido, Japan

This study analyses the steroidal composition of a whale bone and two marine mammal bones of the extinct order Desmostylia from the Oligocene of eastern Hokkaido, Japan. While the desmostylian bones displayed a series of C27-C29 steranes and diasteranes, as well as pregnane (C21 sterane), the whale bone displayed only C27 steranes (cholestane and its isomer coprostane). The desmostylian bones also displayed polyaromatic hydrocardbons (PAHs) that could be indicative of further advanced stages of diagenetic alteration, while such PAHs were not present in the whale bone, which on the other hand displayed several aromatic steroids. These include a secocholestatriene, a noranthracholestene derivative, cholestadiene, and a series of cholestenes. Such aromatic steroids are more associated with intermediary products of diagenesis. We interpret that the diagenetic pathway for the whale bone has progressed only to early-mid diagenetic stages, as opposed to the desmostylian bones, and we opine that fossil bone is possibly a unique medium which warrants further study into mechanisms of lipid diagenesis.