What Fossils Are Telling Us (And What We're Missing)

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What Fossils Are Telling Us (And What We're Missing) About the History of Salmons, Trouts and Chars in Western North America During the Past 20 Million Years

Salmonine fishes comprise our familiar trouts, chars and salmons as well as some more unfamiliar fishes like lenok and huchen in eastern Asia. Prior to marine fish-farming, salmonines were native to the northern hemisphere only. They have high metabolic oxygen requirements, which restrict them to cold water habitats. We will look at the utility and the limitations of the fossil record of salmonine fishes over the history of western North America, primarily during the past 20 million years. The earliest discovered salmonine fossil comes from isolated small lake deposits in the Pacific Northwest, during the Eocene, at time of global warmth. Global climate cooled stepwise during the past 30 million years. Over that interval, the present NE Pacific ocean current system took shape. Simultaneously, our current tectonic plate motion dynamic was initiated, leading to the ongoing disassembly of the Cordilleran orogenic belt—an incredibly wide mountain belt that had been constructed over a time span of +100 million years. With the cooling of climate, changing ocean current dynamics, and the changing nature of drainage connections, salmonines penetrated further south along the Pacific coast of North America and into many environments in the Middle and Southern Rockies, the Great Basin, and the ancestral Snake River. A large Pliocene lake the size of current Lake Erie in southwestern Idaho exhibits a phenomenal diversity of salmonine fishes. We will look at many elegant salmonine fossils and what they are telling us about the evolving biodiversity of salmonines, necessarily coupled to tectonic influences on drainage basins and the cooling of marine and fresh waters.

Presenter: Ralph Stearley, Calvin University

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