North American Pennsylvania Conodont Biostratigraphy

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Abstract
Investigations in the southern Midcontinent, the southwestern United States, and the central Appalachians demonstrate the potential biostratigraphic value of North American Pennsylvanian conodonts. Morrowan conodonts from the Boston and Arbuckle Mountains in the southern Midcontinent reveal four biostratigraphic units characterized, in ascending order, by Spathognathodus muricatus, Idiognathoides noduliferus, Gnathodus bassleri symmetricus, and Gnathodus bassleri bassleri. The first occurrence of Idiognathoides noduliferus (⇌ Streptognathodus noduliferus and Gnathodus noduliferus of authors) indicates basal Morrowan. In addition, Idiognathodus dominates in the upper Morrowan. In the Great Basin, the first occurrence of Streptognathodus noduliferus is immediately above the Mississippian-Pennsylvanian boundary. The Streptognathodus noduliferus-Idiognathoides convexus Assemblage Zone characterizes most of the Morrowan, and its lower part corresponds to the I. noduliferus unit in the southern Midcontinent. Gnathodus bassleri does not occur above the Atokan, and Gnathodus roundyi ranges from Desmoinesian through Virgilian. In the central Appalachians, the Pennsylvanian Gnathodus lineage begins with Gnathodus noduliferus and reaches its maximum morphologic complexity in G. bassleri bassleri (upper Pottsville). Subsequently, the group gradually simplifies by loss of ornamentation to Gnathodus dilatus in the upper Allegheny. Streptognathodus seems to have been both successor and ancestor of Idiognathodus several times. Biostratigraphic subdivision of the Conemaugh Group is based on the evolution within Streptognathodus because Idiognathodus rarely occurs in the upper Conemaugh where Streptognathodus attains its maximum development.

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