Current salmonids comprise three
lineages, taxonomically treated as subfamilies: whitefish (
Coregoninae), graylings (
Thymallinae), and the
trout, and salmons (Salmoninae). Generally, all three lineages are accepted to allocate a suite of derived traits indicating a
The Salmonidae first appear in the fossil record in the middle
Eocene with the
Eosalmo driftwoodensis, which was first described from fossils found at
Driftwood Creek, central
British Columbia. This genus shares traits found in the Salmoninae, whitefish, and grayling lineages. Hence, E. driftwoodensis is an archaic salmonid, representing an important stage in salmonid evolution.
A gap appears in the salmonine fossil record after E. driftwoodensis until about seven million years ago (mya), in the late
Miocene, when trout-like fossils appear in
Idaho, in the
Clarkia Lake beds.
 Several of these species appear to be
Oncorhynchus—the current genus for Pacific salmon and some trout. The presence of these species so far inland established that Oncorhynchus was not only present in the Pacific drainages before the beginning of the
Pliocene (~5–6 mya), but also that
cutthroat trout, and Pacific salmon lineages had diverged before the beginning of the Pliocene. Consequently, the split between Oncorhynchus and
Salmo (Atlantic salmon) must have occurred well before the Pliocene. Suggestions have gone back as far as the early Miocene (about 20 mya).