FOSSIL RECORD OF PACIFIC SALMON, ONCORHYNCHUS

Pacific salmon and trout are represented by excellent specimens from mid-Miocene to Pleistocene sediments in Washington, Oregon, California, and Idaho. The salmon are related to chum, pink, and sockeye. The age of the group raises interesting evolutionary problems--molecular biologists describe the evolution of Pacific salmon as Pleistocene examples of rapid evolution, but the fossil record documents extremely slow rates of evolution, probably as a consequence of unstable environments. Excellent specimens of the giant saber-tooth salmon, 6-14 Ma, the landlocked dwarf sabertooth, and the Idaho sockeye, 6 Ma, are among the most morphologically advanced salmon. Trout and a species similar to chum salmon are known from 6 Ma sediments in E Oregon and W Idaho. Remarkable specimens from the middle Pleistocene of the Olympic Peninsula are large sockeyes that share some features with pink salmon. Stable isotopes in bone suggest migratory and landlocked life history traits that evolved in rivers and lakes of the active plate margins around the Pacific Rim.