Temporal range: Middle Eocene 
|Eosalmo driftwoodensis, Klondike Mountain Formation, Washington, USA|
The genus was first described in 1977 from fossils found in lacustrine deposits in Driftwood Canyon Provincial Park, near Smithers, British Columbia, Canada, leading to the specific epithet E. driftwoodensis. Fossils from this genus have also been found at sites in Princeton, British Columbia, the McAbee Fossil Beds in B.C., and Republic, Washington, USA.
When first described the genus was thought to be intermediate in form to the living salmon subfamilies Salmoninae (trout and salmon) and Thymallinae (graylings). More recent review of the genus has placed Eosalmo as the most primitive member of the Salmoninae subfamily. Fossils found in Driftwood Canyon Provincial Park display a full range of individuals from young juveniles through adults. This range indicates that the genus was completely freshwater dwelling and did not spend time in saltwater.
Several unique characters found in Eosalmo separate the genus from extant salmonids. The subopercle exhibits an anetrodorsal process which meets the edge of the subopercle at approximately a 60° angle. Also unique is the basihyal tooth plate, which is broad, flat, thin, and lacking any teeth along the edges. Modern salmonids possess stout teeth along the edge of the basiyal. The morphology suggests Eosalmo represents an intermediate between the modern Salmoninae and Thymallinae subfamilies and evolved from a grayling like ancestor.
- Sepkoski, J (2002). "A compendium of fossil marine animal genera". Bulletins of American Paleontology. 364: 560. Archived from the original on 2011-07-23. Retrieved 2009-02-27.
- Wilson, MVH (1977). "Middle Eocene freshwater fishes from British Columbia". Life Sciences Contributions, Royal Ontario Museum. 113: 1–66.
- Wilson, MVH; Li, Guo-Qing (1999). "Osteology and systematic position of the Eocene salmonid †Eosalmo driftwoodensis Wilson from western North America" (PDF). Zoological Journal of the Linnean Society. 99 (125): 279–311. doi:10.1111/j.1096-3642.1999.tb00594.x. Retrieved 2010-01-01.
- Burke Museum Eosalmo page
- "Geological Survey of Canada". nrcan.gc.ca. Retrieved 11 April 2018.
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