253-9 Late Desmoinesian to Missourian Platformed Species of Gondolella from the Type Region and Interval of Stauffer and Plummer (1932), Brazos River Valley, Texas

Session: Conodonts from North America and Beyond - Honoring the Career of Dr. James E. Barrick

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Abstract:

The taxonomy of Gondolella species has proven challenging over the decades. The typical addition of new species over time and two substantial revisions (Clark and Mosher, 1966; Merrill and von Bitter, 2007) have not improved the confidence in the species concept or existing taxonomic schemes. A detailed investigation of element characteristics and variation has enabled a new approach to species designation over the original stratigraphic interval of Stauffer & Plummer in type region of north-central Texas. Collections from the East Mountain Shale, Upper Salesville Shale, and the Posideon Shale have been used to catalog characteristics and evaluate Late Desmoinesian to Middle Missourian platformed Gondolella species. Gondolella magna, G. bella, and G. sublanceolata are present in the upper portion of the East Mountain Shale. All three species range into the Upper Salesville Shale. Gondolella elegantula is first recovered in the Posideon Shale, in Texas, where it occurs with both G. sublanceolata and G. bella. Gondolella sublanceolata increases in abundance from older to younger levels. Gondolella bella is most common in the East Mountain Shale and decreases to a few rare specimens in the Posideon Shale. Even at the greatest abundance of G. bella, the more characteristic crenulate species of G. magna and the later G. elegantula tend to dominate gondolellid faunas. Gondolella species fill three distinct morphological classes: narrow forms (G. bella, G. elegantula), lanceolate forms (G. sublanceolata), and broad forms (G. magna,). In this interval, the narrow forms undergo a replacement of the Late Desmoinesian G. bella with the Missourian G. elegantula. In the Late Desmoinesian, the beveling of platform margins is uncommon in most forms, typically only appearing in the largest specimens. Edge beveling becomes more common in all forms, even in smaller specimens, in the Missourian. Similarly, complex transverse ridge patterns, including bifurcation and intersecting ridges, become more frequent. Specimens may exhibit a secondary dorsal cusp adjacent to the primary cusp, rarely; a condition that exists in all Gondolella species of this interval.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9244

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