During the Miocene and Pliocene epochs, the Pacific coast of North America was home to the saber-toothed salmon, Oncorhynchus rastrosus. It is the largest species of salmon known to have existed, a giant that inhabited an ancient ocean shared with other massive creatures. First appearing in the late Miocene, this prehistoric salmonid carved out a niche for itself in the Pacific ecosystem before its eventual disappearance.
Physical Description
The size of Oncorhynchus rastrosus sets it apart from any salmon living today. Fossil evidence indicates these fish could reach lengths of up to nine feet and weigh nearly 400 pounds, making them a giant member of the salmon family. The discovery of their remains, primarily partial skulls, has allowed paleontologists to piece together a picture of this formidable creature.
The most distinctive feature of this salmon was its “saber teeth.” Initially, scientists believed these large teeth pointed downward from the snout, which led to its common name. However, more complete fossil discoveries revealed a different orientation. The teeth, more accurately described as spikes or tusks, projected sideways from the snout.
These spiked teeth were present in both males and females, though they were larger in males. The fish’s scientific name, Oncorhynchus rastrosus, translates to “spike-nosed salmon.” The teeth themselves could measure between two and three centimeters long. This physical trait developed as the salmon matured, particularly as it prepared for its migration into freshwater.
Habitat and Diet
The saber-toothed salmon had a broad geographic range, with fossils discovered along the Pacific coast from California to Washington, and even in Japan. Like their modern relatives, these fish were anadromous. This means they spent most of their adult lives in the saltwater of the Pacific Ocean before migrating into freshwater rivers to spawn. They navigated ancient river systems in what is now California.
Despite its fearsome name and prominent teeth, evidence points to a surprising diet. Oncorhynchus rastrosus was a filter-feeder, subsisting primarily on plankton. This conclusion is based on the discovery of numerous, finely-built gill rakers in fossilized remains. These structures are used to strain small organisms from the water, and the salmon’s were much larger and more numerous compared to most modern, predatory salmon species.
The abundance of plankton in Miocene oceans supported the salmon’s massive size. A filter-feeding lifestyle conserved energy that could be directed toward growth. This dietary strategy is not entirely unique, as the modern sockeye salmon, Oncorhynchus nerka, also feeds on plankton as an adult.
The Purpose of the Saber Teeth
The presence of large, spiked teeth on a plankton-eating fish presents a biological puzzle. Scientific hypotheses focus on social functions related to their life cycle. The leading theory suggests the teeth were used for combat and display, particularly between males competing for mates or defending territory during the spawning season.
Fossil evidence supports this idea, showing that teeth from freshwater deposits are larger and show more wear than those from marine environments. This suggests the teeth grew and were used most actively after the salmon entered rivers to breed. The powerful side-to-side motion salmon use for swimming could have been adapted to swing these spikes against rivals.
Another possibility is that the salmon used their tusks to help dig out nests, known as redds, in the gravel of riverbeds. Modern salmon use their tails for this purpose, but the addition of tusks could have been an effective tool. The use of the teeth for fighting, display, or nest-building are the most plausible explanations.
Extinction and Modern Relatives
The saber-toothed salmon became extinct several million years ago, around the transition from the Pliocene to the Pleistocene epoch. The most widely accepted cause for its extinction is significant environmental change. A period of global cooling led to the expansion of glaciers, which would have drastically altered both the ocean currents and the freshwater river habitats that the species depended on for spawning.
Oncorhynchus rastrosus belongs to the same genus, Oncorhynchus, as all modern Pacific salmon and trout. This classification makes them relatives, but the saber-toothed salmon represents a distinct, extinct branch of the family tree. It is not a direct ancestor to any salmon species that exists today.