Eothynnus salmonens is an extinct species of prehistoric jackfish

Carangidae

Carangidae is a family of fish which includes the jacks, pompanos, jack mackerels, and scads.They are marine fish found in the Atlantic, Indian and Pacific Oceans...

 that lived during the lower Eocene

Eocene

The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...

 of what is now the Isle of Sheppey

Isle of Sheppey

The Isle of Sheppey is an island off the northern coast of Kent, England in the Thames Estuary, some to the east of London. It has an area of . The island forms part of the local government district of Swale...

 (as a part of the London Clay

London Clay

The London Clay Formation is a marine geological formation of Ypresian age which crops out in the southeast of England. The London Clay is well known for the fossils it contains. The fossils from the Lower Eocene indicate a moderately warm climate, the flora being tropical or subtropical...

 Lagerstatten. It is known exclusively from some preserved skulls.

It was originally thought to be a tuna

Tuna

Tuna is a salt water fish from the family Scombridae, mostly in the genus Thunnus. Tuna are fast swimmers, and some species are capable of speeds of . Unlike most fish, which have white flesh, the muscle tissue of tuna ranges from pink to dark red. The red coloration derives from myoglobin, an...

 or mackerel

Mackerel

Mackerel is a common name applied to a number of different species of fish, mostly, but not exclusively, from the family Scombridae. They may be found in all tropical and temperate seas. Most live offshore in the oceanic environment but a few, like the Spanish mackerel , enter bays and can be...

, hence the generic name translating as "dawn" or "Eocene tuna." Later, it was reappraised to be a jackfish, related to Teratichthys and Eastmanalepes

Eastmanalepes

Eastmanalepes primaevus is an extinct species of prehistoric jack fish that lived from the Lutetian epoch, of what is now Monte Bolca, Italy. It was originally described as a species of the jackfish genus Caranx, of which it has a superficially similar outline to...

(syn. "Caranx

Caranx

Caranx is a genus of tropical to subtropical marine fish in the jack family Carangidae, commonly known as jacks, trevallies and kingfishes. They are moderate to large sized, deep bodied fishes which are distinguished from other carangid genera by specific gill raker, fin ray and dentition...

 primaevus").

See also

• Prehistoric fish
  Prehistoric fish
  Prehistoric fish refers to early fish that are known only from fossil records. They are the earliest known vertebrates, and include the first and extinct fish that lived through the Cambrian to the Tertiary. The study of prehistoric fish is called paleoichthyology...
  
  
• List of prehistoric bony fish