A New Marine Vertebrate Assemblage From the Wilson Grove Formation at Bloomfield Quarry (Late Miocene), Sonoma County, California

SMC Author

Douglas Long

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School of Science



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Journal of Vertebrate Paleontology


A relatively diverse assemblage of at least 17 vertebrates (three species of sharks, three genera of teleost fishes, nine marine mammals, and at least two species of bird) is reported from the basal Wilson Grove Formation in a small quarry just north of the town of Bloomfield in Sonoma County, California. The vertebrate, as well as associated invertebrate, assemblages suggest intertidal to shallow subtidal water depths and water temperatures interpreted from the fauna are consistent with the latitude of the fossil locality (37°N) during the late Miocene. A single Sr isotope age determination of 7.92 Ma is consistent with other age determinations bounding the deposits and with interpretations based on vertebrate and invertebrate biostratigraphic data. The age of these vertebrate remains facilitates comparisons with better-known Miocene vertebrate assemblages from other parts of western coastal North America. The ichthyofauna is indicative of the relatively recent northeastern Pacific assemblages that originated in the late Miocene, and each of the species of sharks (Hexanchus griseus, Cetorhinus maximus, Isurus oxyrhynchus) and genera of bony fishes (Sardinops, Merluccius, Sarda) collected at this site, are still found in California coastal waters. The marine mammals from this location include the most diverse walrus assemblage yet reported in the world, including Dusignathus santacruzensis, Gomphotaria pugnax, Imagotaria sp., cf. Pontolis, and Odobeninae indet. Indeterminate odontocetes, balaenopterid and herpetocetine mysticetes, and an indeterminate hydrodamaline sea cow are also reported. The marine mammal assemblage has affinities with those from the Capistrano, Purisima, and San Mateo formations of California. Bird remains are reported from the Wilson Grove Formation herein for the first time. There are at least two species of bird represented by five specimens from the Bloomfield Quarry location. These specimens have been referred to Aves indet., Pan-Alcidae indet., Mancallinae indet., and cf. Uria brodkorbi. The combination of precise chronological age and detailed knowledge of both vertebrate and invertebrate assemblages from Bloomfield Quarry provide a rare snapshot of the shallow marine ecosystem of northern California during the late Miocene.





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Original Citation

Smith, A.N., Boessenecker, R. J., Long, D. J., Powell II, C. “A new marine vertebrate assemblage from the Wilson Grove Formation at Bloomfield Quarry (late Miocene), Sonoma County, California.” Journal of Vertebrate Paleontology, 37,1 95. 2017.