Megalodon
Marine mammals were regular prey targets for megalodon. Many whale bones have been found with clear signs of large bite marks (deep gashes) made by teeth that match those of megalodon, and various excavations have revealed megalodon teeth lying close to the chewed remains of whales, and sometimes in direct association with them. Fossil evidence of interactions between megalodon and pinnipeds also exist. In one interesting observation, a  megalodon tooth was found lying very close to a bitten earbone of a sea lion.