Almost everyone has heard about sabretooth cats, mostly thanks to the incredibly fun Ice Age movie series with the cool cat, Diego. But it wasn’t the only sabre toothed beastie of the Pleistocene. There was of course, the more unfamiliar British sabretooth, Homotherium. But there was something else….lurking in the waters…. something really, really big. I present to you one of the real oddities of the Pleistocene, Oncorhynchus rastrosus (synomyn Smilodonichthys rastrosus) – the sabre toothed salmon.

Yes, you read that correctly.

Salmon.

Sabre toothed.

And they were really large. This is no fish-tale. O. rastrosus was around 2m long; although, according to fossil evidence, many grew well beyond 3m in length. The teeth are the main feature of this huge fish – the synomyn species name is derived from the huge protruding canine teeth jutting from its top jaw, resembling the fangs of Smilodon. Now, all male salmon have these little upper teeth, mostly used to see off other males during the spawning season but nothing comparable to the fangs of the giant sabre tooth salmon. Appearance-wise, this giant of the Pacific northwest rivers resembled the modern sock-eye salmon; genetically they’re not terribly far removed from each other. There’s some debate about just how close the genetic links are: Oncorhyncus rastrosus and Smilodonichthys rastrosus are pretty much the same critter, with Oncorhyncus being the more ‘correct’ nomenclature, though as I was told by one of its fans, S. rastrosus is much cooler!

Not the greatest of images of the sabretooth salmon ever, but it shows the size of those big teeth. Although they are depicted here as pretty ferocious fish, they actually fed on the tiny little organisms that float in the water, the plankton.

They are creatures whose lives are shrouded in mystery. Despite the first fossil skulls being found in 1917 in Oregon, we know very little about their habits, or even an accurate date of extinction.  It’s commonly believed they migrated from the deep freshwater rivers of Oregon and California out to the Pacific to feed on microscopic marine organisms. As this is one of the ‘original’ salmonids, palaeontologists – and palaeoichthyologists for that matter! –  have been keen to try and work out if the taxa began as freshwater or marine creatures, to try and understand the dramatic spawning migration patterns and paths which our modern day salmon still perform. There’s been palaeomagnetic analysis carried out on lake sediments where O. rastrosus once lived, as of course, migration is influenced by magnetoception ( the ability to use earth’s magnetic fields to locate the region where spawned themselves) – if a wobble or change in that field occurs, migration will be a bit messed up. As we know there have been several magnetic ‘ wobbles’ over deep prehistory, lake sediment analysis can hopefully create a  more solid chronology of when this giant salmon ruled the rivers of northwest America. If anyone has ever watched the event of salmon sprinting and splashing up rivers, they’ll know it’s an amazing, and quite awe-inspiring thing to witness. Now imagine how majestic and exciting it would be to see a fish up to 3 metres long, leaping from the waters of deep, fast rivers, making its way back to its place of birth, to start the cycle of reproduction all over again.

In truth, we aren’t even quite sure of the exact period of the Pleistocene in which the sabre tooth salmon became extinct, but it is suspected that its demise is linked to climate change, which makes it a pretty important story to compare to our own world today. There’s been surprisingly little modern research on this amazing fish, despite the modern interest in all things pertaining to climate change and sea level changes.  One of the more recent papers, however, by Stearley and Smith in 1993, suggests that this enormous fish was indeed a migratory (or anadromous) species, which makes it likely that its demise during the Pleistocene was caused by changes in sea-temperatures and subsequent declining micro-organisms to feed off.  The sabre tooth salmon started off as a Miocene creature, perhaps 12 million or more years ago, and landscapes were different; more importantly, climate was different. The stomping grounds (or splashing grounds?) of this giant salmon were deep lakes and rivers created by seismic activity of deep prehistory. By the very end of the Miocene period, the northern hemisphere was getting colder. The Pleistocene saw the beginnings of further climate fluctuations, which of course would create the glaciation event we call the Ice Age.  Colder seas and rivers meant less available plankton for O. rastrosus.  There were also sea level changes and alterations to inland waterway hydrology systems, especially as glaciation encroached across North America. We know from Smith et al’s paper of 2007 there were still specimens swimming around Oregon around 700,000 years ago, but the fact is, we just don’t know exactly how long into the Quaternary O. rastrosus survived.

Palaeoenvironmentally, this fish is the one that got away. We’ve no idea if any human ever set eyes on this massive fish leaping from the clear waters. It is one of the few creatures where we can probably state that humankind was not involved in some way in its extinction. Yet there is so much we still have to learn about this plankton eating gentle giant of the Pleistocene, and it does seem to be a fabulous PhD or postdoctoral study just waiting for someone to come along and take the bait! Because it’s likely S.rastrosus required similar environmental conditions to modern salmon, its story could hold huge implications for extant species in the light of our changing environment and climate.

Addendum: A huge thanks to @smilodonichthys who checked this for the most up-to-date facts over in Oregon!  We’re hoping to persuade  our Twitter pal to blog the discovery of fully fanged skulls on one of their expeditions! Meantime, there’s @smilodonichthys ‘ s dad’s blog here to check out fishy fossily frolics in the gorgeous northwest of the US!  http://bernietheichthyosaur.blogspot.com/

Written by Rena Maguire (@JustRena)

Further Reading:

Brown, B, (1995), Mountain in the clouds: a search for the wild salmon. Washington: University of Washington Press. [Book]

Casteel, R. W, (1974), ‘Use of Pacific salmon otoliths for estimating fish size, with a note on the size of late Pleistocene and Pliocene salmonids’. Northwest Science. 48.3: 175-179. [Full article]

Casteel, R. W., & Hutchison, J. H. 1973. ‘ Orthodon (Actinopterygii, Cyprinidae) from the Pliocene and Pleistocene of California’. Copeia 358-361. [Full article]

Cavender, T.M., and Miller, R.R. (1972), ‘Smilodonichthys rastrosus: A new Pliocene salmonid fish from western United States’. Museum of Natural History, University of Oregon, Bulletin 18:1-44. [Full article]

D.J. Easterbrook, J.L. Roland, R.J. Carson, N.D. Naeser. (1988) ‘Application of paleomagnetism, fission-track dating, and tephra correlation to Lower Pleistocene sediments in the Puget Lowland, Washington’ in Easterbrook, D.J (Ed.) Dating Quaternary Sediments, Geological Society of America Special Paper. 227:139–165. [Abstract only]

McDowall, R. M. (2001), ‘The origin of the salmonid fishes: marine, freshwater… or neither?’ Reviews in Fish Biology and Fisheries.  11. 3: 171-179. [Abstract only]

Smith, G.R; Morgan, N and. Gustafson, E. 2000. ‘Fishes of the Mio-Pliocene Ringold Formation, Washington: Pliocene Capture of the Snake River by the Columbia River’ University of Michigan Museum of Paleontology Paper. 32: 1–47. [Full article]

Smith, G. R; Montgomery, D. R; Peterson, N & Crowley, B. (2007), ‘Spawning sockeye salmon fossils in Pleistocene lake beds of Skokomish Valley, Washington’. Quaternary Research 68.2: 227-238. [Full article]

Stearley, R.F and Smith, G.R. (1993), ‘Phylogeny of the Pacific trout and salmon (Oncorhynchus) and genera of the family Salmonideae’. Transactions of the American Fish Society. 122: 1-33. [Full article]

Maher, J. C., Trollman, W. M., & Denman, J. M. (1973). Geological Literature on the San Joaquin Valley of California. USGS. [Book]