Bizarre sea mammals related to dolphins - but more closely related to Narwhals. These animals we up to 3 metres long, and they dwelt in thick kelp forests off the coast of Peru. They were the prey of juvenile Megalodon sharks. The males sported two tusks - one 30 cm or so in length, and oddly the other 4 feet in length. The purpose of such weird tusks is not fully understood, though it is suggested most likely that males 'jousted' with each other, using them to lock together in battles over females. They were however generally gentle marine bottom feeders, sucking up molluscs from the seabed. They lived in the Pliocene Epoch, 6-3 Million Years Ago.