This 8-foot-long ‘saber-toothed’ salmon wasn’t quite what we thought

When paleontologists announced the discovery of the largest salmon to have ever lived in 1972, they thought they had found the aquatic equivalent of the saber-toothed cats that roamed the landscape when this fish was alive between 12 and 5 million years ago.

The eight-foot-long fish was believed to have had two curved teeth jutting down from its upper jaw. But now, a new reconstruction has fundamentally altered the face of this iconic fish, proposing instead that its impressive teeth stuck out sideways from its snout—like a warthog.

In an April study published in PLOS ONE, experts present a new vision of the spike-toothed salmon, formally known as Oncorhynchus rastrosus. The changes to the salmon’s face reflect new knowledge about the fish gleaned from the fossil record. In 2016, paleontologists found that the ancient salmon’s distinctive teeth changed as the fish aged, growing as the salmon reached adulthood and transitioned from the sea to freshwater. 

This study, by Philadelphia College of Osteopathic Medicine paleoecologist Kerin Claeson and colleagues, now finds that the fish’s famous teeth stuck out sideways like tusks.

A bold new look

Refining what the fish looked like rested on both new fossil finds and a reanalysis of the first fossils to be described half a century ago. Among the earliest finds, the part of the jaws holding the prominent teeth were disarticulated from the rest of the skull. “Part of the reason why scientists didn’t recognize the position of the teeth at first was because they were all found in isolation,” Claeson says. A downward, saber-like position seemed reasonable given that no other known fish had such teeth. 

But in 2014, paleontologists searching a locality in Oregon found new fossil skulls of Oncorhynchus rastrosus that showed the prominent teeth still in articulation. Combined with CT scans of the original finds, the new fossils confirmed that different sexes of the spike-toothed salmon had the prominent teeth in adulthood.

Finding the spikes on different salmon sexes came as a surprise to the researchers. “When I talked to the collectors of the 2014 fossils, they kept finding fossils in close proximity in such a way they were likely breeding pairs, which both possessed the enormous spikes,” Claeson says. All spike-toothed salmon started to go through skull changes as they approached adulthood, each fish growing the iconic spikes.

“The new reconstruction is supported by very convincing evidence,” notes University of Alberta paleontologist Mark Wilson, who was not involved in the new study. The fact that the spikes were found as a species-wide trait, he noted, is especially remarkable.

Naturally, the unusual nature of the spikes has led paleontologists to wonder why such features evolved and what they were used for. Previous research indicated that some of the teeth in adult fish were blunted and worn, hinting that they were rubbing against hard surfaces. Perhaps the fish were using the teeth to scrape and move sediment in constructing nests, and could have also been helpful in defending those nests from other fish looking to dig their own divots in the riverbed.

Claeson and colleagues prefer a defensive function for the spikes. The prehistoric salmon, just like their living counterparts, swam with side-to-side motions of the body. Their strongest muscles were devoted to these movements, and also would have allowed the fish to take strong swings against predators or other rivals. Not all experts agree, though. Wilson notes that the fish could have been using the spikes to dig nesting areas, and males could have been using the spikes to intimidate competitors for mates during spawning season. 

Regardless of whether the fish were using the spikes for defense or in competition, the teeth were surely formidable. “Imagine a one-pound geology hammer, sharpened, and wielded by 200 pounds of lateral muscle,” Claeson says. The salmon is no longer a sabertooth, but its teeth were just as formidable.