A Million Year Old Salmon
The original fossil of this fish, Oncorhynchus nerka, was found in sediments of an ancient lake bed along with several other adult fish. The discovery was made locally on the east side of the Olympic Peninsula.
The fish may have been on their way to spawning grounds when a dramatic event blocked their passage and quickly covered their bodies, preserving them for one million years. Scientists at the University of Washington are studying these fossils and the sedimentary materials in which they were found to better understand salmon and their evolutionary history.
Originally, there may have been just one stock of salmon, located in the Atlantic Ocean. Current fossil evidence suggests that connections across the Arctic Sea allowed ancient Atlantic salmon to migrate west more than 14 million years ago, permitting the Pacific salmon stock to evolve.
Paleontologists believe that salmon originally were exclusively freshwater fish. As oceans cooled during the last 25 million years, their waters contained a greater abundance and variety of food. To take advantage of this food resource, salmon developed the ability to move from rivers to the vast, rich pastures of ocean.
The fossil on exhibit is an ancient example of Oncorhynchus nerka, or sockeye salmon. Today we recognize five different species of Pacific salmon: chinook, chum, coho, sockeye, and pink. Within the same genus, we also find steelhead and cutthroat. These different species appear to have diverged from each other six million years ago.
During recent times of glaciation (2 million- 15,000 years ago), salmon not only survived major episodes of advancing and retreating ice that made many rivers inaccessible, but catastrophic floods that dramatically changed entire landscapes.
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"To fully appreciate the salmon's resilience, we must understand their evolutionary history and the episodes of cataclysmic environmental change they have survived."
Jim Lichatowich
Salmon Without Rivers