219-6 Implications of a diverse ophiuroid fauna from the Late Mississippian Pitkin Fm., Oklahoma

Session: Paleontology, Diversity, Extinction, Origination (Posters)

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Abstract:

The Upper Mississippian (Viséan) preserves an ophiuroid fauna transition from faunas dominated by archaic species to ones dominated by members of the modern fauna (Metophiurida). New approaches applied to Carboniferous ophiuroids have transformed our understanding of the timing of the emergence of the modern brittle star fauna. Rather than relying on the identification of rarely preserved articulated specimens, new methods utilize lateral arm plates (LAPs) in a similar manner to how distinctive conodont elements are used. The use of LAPs facilitates the identification of multiple species and genera in the Pitkin fauna. The fauna includes two stenuroid species, Umerophiura n. sp. characterized by paddle-shaped LAPs and Antiquaster sp. with elongate boot shaped LAPs. Protasterids include two Schoenaster species that differ in the plate outline and the vertebral articulations on the interior surfaces, and a newly identified spineless protasterid sp. Three furcasterid species, including a broad, paddle-shaped LAP characteristic of Cholaster sp., Furcaster sp. 1 which consists of narrow, triangular LAPs with complex spine articulations with scalloped distal margins, and Furcaster sp. 2 that has triangular shaped LAPs with large, weakly developed distal spine bases. Two cheiroptasterids species include Vandelooaster sp. with elongate triangular LAPs and Loriolaster sp. bearing rounded L-shaped LAPs. Three metophiurids species include Archaeophiomusium n. sp. with thick, arched and tumid LAPs, Sulphaster sp. with small, thin, arched LAPs with well-developed spine bases, and Suchaster sp. with thick rectangular LAPs with three spine bases. The Pitkin assemblage marks the shift from faunas numerically dominated by archaic taxa to those dominated by metophiurids. While older faunas include metophiurid species, they are always outnumbered by archaic taxa. The Pitkin Fauna includes eight archaic species and three metophiurid species. In terms of species abundance, however, the metophiurids dominate LAP counts with Archaeophiomusium being especially abundant, comprising 94.1 percent of LAPs in the >2 phi size range. Furthermore, metophiurids are nearly the only LAPs recovered in the 3 phi size fraction. This metophiurid dominance trend continues through at least the early Permian.

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

doi: 10.1130/abs/2025AM-9120

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