The Sabertooth Salmon, Oncorhynchus rastrosus, gets a facelift.
Oncorhynchus (†Smilodonichthys) rastrosus was first named for its incredible premaxillary dentition. Each premaxilla bears an enormous conical tooth, originally reconstructed as canine-like and ventrally directed. However, this giant prehistoric salmon was mistakenly identified as saber-toothed. New, exceptionally preserved specimens from an unnamed latest Miocene or earliest Pliocene deposit in Central Oregon indicate that the premaxillary bones and their enormous dentition were directed laterally rather than ventrally; a feature never observed in any other salmonid. The result is a configuration akin to horns rather than fangs. Here we describe new observations on these additional fossils and contrast them to other Miocene specimens, as well as to modern Eastern Pacific species of Oncorhynchus. Newly discovered morphology includes the presence of accessory dentition on the premaxilla, posterior to the massive premaxillary horn, which is significantly smaller. There is no visible kype on the dentary. On the dentaries, the only teeth are minute, laterally directed and at the mesial ends. These observations, plus the inland freshwater locality and their skeletal maturity imply that these were upstream migratory fishes preparing to spawn. Yet it appears that the metamorphosed spawning morphology observed in modern species is not present. It is probable that some tooth resorption occurred given the paucity of teeth along the dentary, but the lack of outward evidence of a kype may imply a different strategy for indicating mate dominance. The elaborate premaxillary horns may have aided in fights for space or improved the ability to shovel gravel while making redd nests. Alternatively, the lateral teeth may have improved substrate contact allowing the fish to maintain position in stream environments.
Claeson, Kerin M.; Davis, E. B.; Sidlauskas, B. L.; and Prescott, Z. M., "The Sabertooth Salmon, Oncorhynchus rastrosus, gets a facelift." (2016). PCOM Scholarly Papers. 1638.
Abstract of a presentation at the Society for Integrative and Comparative Biology: 2016 Annual Meeting.