Current salmonids comprise three main
clades taxonomically treated as
subfamilies:
Coregoninae (
freshwater whitefishes),
Thymallinae (
graylings), and
Salmoninae (
trout,
salmon,
char,
taimens and
lenoks). Generally, all three
lineages are accepted to allocate a suite of derived traits indicating a
monophyletic group. The suborder Salmonoidei, containing only Salmonidae, is one of two extant clades within the order Salmoniformes, which first appeared during the
Santonian and
Campanian stages of the
Late Cretaceous. The other is the
Esocoidei, which contains the
pikes and
mudminnows. However, as recent phylogenetic studies have affirmed the relationship between the Salmonoidei and Esocoidei, the latter have returned to being considered a suborder of Salmoniformes.
fossilKlondike Mountain FormationIt is thought that salmon and pike diverged from one another during the Cretaceous, but until 2025, there was no fossil evidence of salmonids occurring during this time period. In 2025, the earliest known fossil salmonid, Sivulliusalmo alaskensis, was described from the early Maastrichtian-aged Prince Creek Formation of Alaska, with indeterminate remains of this genus also being identified from the older Campanian-aged Dinosaur Park Formation of Alberta. The occurrence of Sivulliusalmo'' in these northern habitats suggests that the modern salmonid preference for cool, high-latitude waters is an ancient, conserved trait. Prior to the description of
Sivulliusalmo, the earliest record of salmonids was the
Early Eocene-aged
Eosalmo driftwoodensis, a stem-
salmonine, which was first described from fossils found at
Driftwood Creek, central
British Columbia, and has been recovered from most sites in the
Eocene Okanagan Highlands. This genus shares traits found in all three subfamily 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 7 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 Pacific 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
rainbow and
cutthroat trout, and Pacific salmon lineages had diverged before the beginning of the Pliocene. Consequently, the split between
Oncorhynchus and
Salmo (Atlantic salmon and European trout) must have occurred well before the Pliocene. Suggestions have gone back as far as the
Early Miocene (about 20 mya).
Genetics '' maturing from eggs. Based on the most current evidence, salmonids diverged from the rest of
teleost fish no later than 88 million years ago, during the late
Cretaceous. This divergence was marked by a
whole-genome duplication event in the ancestral salmonid, where the diploid ancestor became
tetraploid. This duplication is the fourth of its kind to happen in the evolutionary lineage of the salmonids, with two having occurred commonly to all bony vertebrates, and another specifically in the teleost fishes. The earliest presumed
crown-group salmonid fish (
E. driftwoodensis) does not appear until the middle Eocene. This fossil already displays traits associated with extant salmonids, but as the genome of E.
driftwoodensis cannot be sequenced, it cannot be confirmed if polyploidy was present in this animal at this point in time. Given a lack of earlier transition fossils, and the inability to extract genomic data from specimens other than extant species, the dating of the whole-genome duplication event in salmonids was historically a very broad categorization of times, ranging from 25 to 100 million years in age. New advances in
calibrated relaxed molecular clock analyses have allowed for a closer examination of the salmonid genome, and has allowed for a more precise dating of the whole-genome duplication of the group, that places the latest possible date for the event at 88 million years ago. This more precise dating and examination of the salmonid whole-genome duplication event has allowed more speculation on the radiation of species within the group. Historically, the whole-genome duplication event was thought to be the reason for the variation within Salmonidae. Current evidence done with molecular clock analyses revealed that much of the speciation of the group occurred during periods of intense climate change associated with the last ice ages, with especially high speciation rates being observed in salmonids that developed an anadromous lifestyle. == Classification ==