Eothynnus salmonens is an extinct species of prehistoric jackfish that lived during the lower Eocene of what is now the Isle of Sheppey (as a part of the London Clay Lagerstatten. It is known exclusively from some preserved skulls. It was originally thought to be a tuna or mackerel, hence the generic name translating as "dawn" or "Eocene tuna." Later, it was reappraised to be a jackfish, related to Teratichthys and Eastmanalepes (syn. "Caranx primaevus").