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Late Middle Cambrian Faunas from Western Utah

Richard A. Robison
Journal of Paleontology
Vol. 38, No. 3 (May, 1964), pp. 510-566
Stable URL: http://www.jstor.org/stable/1301528
Page Count: 71
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Late Middle Cambrian Faunas from Western Utah
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Abstract

The Wheeler and Marjum Formations of western Utah contain from 1400 to 1800 feet of limestone and shale in one of the thickest, best exposed, and most fossiliferous successions of upper Middle Cambrian strata in North America. During the present study, seven stratigraphic sections were measured in the House Range and Drum Mountains, fossils were systematically collected, and the stratigraphic positions of all collections were recorded. From the fossils that were collected, 43 species of trilobites, eight species of brachiopods, four species of molluscs, and two species of porifera are described. Three genera and 21 species of trilobites are new. The new trilobite genera are Trymataspis, Utagnostus, and Utaspis, and the new trilobite species are Baltagnostus eurpyx, Bathyuriscus fimbriatus, Bolaspidella contracta, Bolaspidella drumensis, Brachyaspidion sulcatum, Cotalagnostus laevus, Elrathia alapyge, Elrathia marjumi, Hemirhodon amplipyge, Homagnostus incertus, Lejopyge calva, Linguagnostus perplexus, Modocia brevispina, Modocia laevinucha, Modocia nuchaspina, Peronopsis segmenta, Ptychagnostus akanthodes, Trymataspis depressa, Trymataspis lomaleie, Trymataspis pristina, and Utagnostus trispinulus. Abundant silicified specimens have provided new information concerning the morphology and ontogeny of agnostid trilobites. Trilobites from the Wheeler and Marjum Formations belong to the Bolaspidella Assemblage Zone of the "standard" Cambrian biostratigraphic column for North America. Three local assemblage subzones are defined, which from oldest to youngest are named for the index species Bathyuriscus fimbriatus, Bolaspidella contracta, and Lejopyge calva.

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