Ancient saber-tusked salmon with fang-like teeth
An extinct species of giant salmon called Oncorhynchus rastrosus had a pair of front teeth that protruded from the sides of its mouth like tusks, according to new research.
The Oncorhynchus rastrosus lived along the Pacific coast of North America (California, Oregon and Washington) between 11 and 5 million years ago. This extinct species was first described in the 1970s from fossils found in the freshwater Gateway locality of the Madras Formation, near the town of Gateway, Jefferson County, Oregon.
The fish is estimated to reached a length of 2.4 to 2.7 meters and a weight of nearly 177 kg making it the largest member of the Salmonidae family never existed.
This species migrated from the Pacific Ocean to inland rivers to spawn, as salmon do today. Furthermore, it was a planktontivore, thanks to numerous gills and a few small teeth.
But Oncorhynchus rastrosus also had two upper teeth 2-3 cm (0.8-1.2 in) long.
Initially, paleontologists thought that these oversized teeth pointed backwards into the mouth like tusks, largely because fossils of the teeth were found separated from the rest of the skull. This has led to the common name “saber-toothed salmon”.
But thanks to new CT scans and analysis of various Oncorhynchus rastrosus fossils collected over the years, Professor Kerin Claeson of the Philadelphia College of Osteopathic Medicine and her colleagues were able to confirm that the teeth actually pointed sideways out of the fish's mouth, similar to a warthog.
“Consequently, the species should be renamed 'snaketooth salmon, '” the paleontologists said.
“While it's not clear what exactly these teeth were for, we think they were probably used for fighting – against other needle-toothed salmon or to defend themselves from predators – or as a tool for digging nests.”
“It is also possible that the teeth were used for multiple purposes,” they added.
“But it is likely that the teeth were not used to capture prey, as Oncorhynchus rastrosus is believed to have been a filter-feeding animal that fed on plankton.”
“We have known for decades that these extinct Central Oregon salmon were the largest ever to exist. Discoveries like ours show that they were probably not gentle giants,” Professor Claeson said.
“These massive spikes at the tip of the snout would have been useful for defending against predators, competing with other salmon and ultimately building nests to incubate the eggs.”
“I am pleased that we were able to put a new face on the giant bucktooth salmon by bringing the knowledge we gained in the field in Oregon to the world,” said Dr. Edward Davis, University of Oregon researcher and director of the Condon Collection at the University of Oregon Museum of Natural and Cultural History.
“We also point out that both females and males possessed enormous tusk-like teeth. Therefore, both sexes were equally fearsome,” said Professor Brian Sidlauskas, curator of fishes at Oregon State University.
The team's findings were published in the journal PLoS ONE (https://doi.org/10.1371/journal.pone.0300252)
