14 Lost Oceans, Shifting Continents: Interdisciplinary Records of Paleo-Pacific Plate Histories in the American Cordilleras

This session integrates tectonics, petrology, geochronology, stratigraphy, and paleontology to illuminate how Paleo-Pacific plates drove subduction dynamics, crustal evolution, and paleogeographic reconstructions across the complex geological architecture of the American Cordilleras.

Wednesday, 22 April 2026
1:30 PM - 4:00 PM
LMH, Meeting Room

A new occurrence of Oncorhynchus rastrosus (the spike-toothed salmon) in coastal Oregon

Paper number: 14-6
Program: Technical Sessions
Time: 3:30 PM – 3:50 PM

Authors

Abstract

The largest salmon to ever live, Oncorhynchus rastrosus, inhabited the eastern Pacific ranging into the freshwater rivers of Western North America. Despite being the largest member of salmonids, with length estimates of 2.4-2.7 m in length, fossils of this giant salmon are relatively poorly known. Published occurrences are limited to Oregon and California from late Miocene through Pliocene deposits. All but one formation, the San Mateo Fm near San Diego, are inferred to be freshwater sedimentary deposits, backed up by both lithological analyses and isotopic geochemistry. This indicates, like many closely related extant salmon, these giant fish were anadromous, hatching in freshwater before journeying to the ocean for the majority of their lives before returning to freshwater to spawn and die. We herein present a new locality producing multiple fossil vertebrae of the spike-toothed salmon in the Empire Fm at Fossil Point, Coos Bay, Oregon. Fossil Point has produced fossils from at least 1865, the oldest use of the name, with the LACM, UCMP, UO, & CAS museum collections holding significant amounts. Most fossils are marine invertebrates, with bivalves, gastropods, echinoderms, and crustaceans common, but the site is also well known for marine mammals including pinnipeds and cetaceans. Lithology, geochemistry, and paleontology of the site indicate a wholly marine setting, unlike even the estuarine setting of the San Mateo. We utilize clastic analysis coupled with XRF geochemical analyses to estimate water depth and other marine parameters to further support the palaeoecological interpretation of this site. We are also extracting lipids from sediments surrounding fossil material that could help to illuminate the depositional setting. While the spike-toothed salmon material is currently limited to vertebral elements, identifying its presence at the site expands of understanding of the ecology of this taxon, will hopefully facilitate the identification of this charismatic fish in more localities with similarly limited material, and even shed insight into nutrient cycling in the Mio-Pliocene of Western North America.

Geological Society of America Abstracts with Programs. Vol. 58, No. 3

doi: 10.1130/abs/2026CD-411029

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