Some 5 to 11 million years ago, the waters of the Pacific Ocean held salmon that topped out at about 9 feet long ("only" three feet for the shorter ones). What's more, they sported inch-long teeth that were wide at the base and shaped like sharpened spikes.
That's according to scientists from California State University, who spoke about the ancient fish at a meeting of the Society of Vertebrate Paleontology.
"These giant, spike-toothed salmon were amazing fish," said Julia Sankey, who led a team of researchers in a study of the extinct creatures. "You can picture them getting scooped out of the proto-Tuolumne River [near Modesto in central Calif.] by large bears 5 million years ago."
And that scooping must have been a tricky task. Even large bears would likely have had their paws full: The super-salmon could weigh up to 400 pounds.
RELATED: Genetically Modified Salmon Safe to Eat, Says U.S.
The unusual teeth of the giant fish were the focus of the team's work. The researchers think it's likely the fish was a filter feeder, just like modern sockeye Pacific salmon, which open wide and take in plankton as they move.
If not for dining, what, then, was the purpose of the teeth?
To find out, Sankey and her colleagues compared dozens of tooth fossils from the animal that were found in freshwater and saltwater environments. The freshwater teeth were longer and more sharply curved, with clear evidence of wear, while those from saltwater sites were consistently smaller and lacked the worn-down look, indicating there was a change in the teeth before spawning.
That difference told the researchers that the large, spiky teeth were likely used for displaying and fighting among the giant salmon during spawning season. The finding dovetailed nicely with the behavior of most modern salmon species. Born in freshwater rivers and streams, they head out to salt water to live much of their lives, before moving back upstream to fresh water to spawn, after which all Pacific salmon and many other species die in a matter of weeks.
Before they migrate, though, salmon undergo physical changes, particularly to their skulls, the researchers noted. And modern males will fight with each other in defense of eggs they have fertilized. The ancient giant salmon, then, had particularly rough-house weapons at its disposal.
WATCH VIDEO: Should You Avoid Farmed Fish?