219-7 A DIVERSE ASSEMBLAGE OF OPHIUROIDS FROM THE EARLY MISSISSIPPIAN (TOURNASIAN) MEADVILLE SHALE MB. OF THE CUYAHOGA FM., OH.

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

Presenting Author:

Authors:

Abstract:

Ophiuroids have the greatest number of species among the five extant echinoderm clades and are found in all of the world’s oceans. However, their skeletal elements (plates) are loosely articulated by soft tissues, resulting in a very low preservation potential for articulated specimens. However, our current understanding of Paleozoic brittle stars is based on these rarely preserved fossils, and their poor preservation potential has limited our ability to explore their past diversity, where taxonomy has traditionally relied on whole-specimen data. These fossils often occur in small numbers, suggesting that diversity estimates are biased and underestimate true diversity.

Emerging methodologies utilizing disarticulated plates—specifically lateral arm plates (LAPs)—have begun to reveal previously unknown levels of Paleozoic ophiuroid diversity. Here, we explore and compare ophiuroid diversity of both articulated and LAP sample sets from the Lower Mississippian (Tournasian) Meadville Shale Member of the Cuyahoga Formation, Lodi, Medina Co., OH, which has previously produced echinoderm fossils with excellent preservation. Articulated brittle star fossils are rare at the locality, and a suite of 20 articulated specimens was collected over several years. Microfossil samples were processed from the locality by soaking fossiliferous shale in hydrogen peroxide and wetting agents to disaggregate the shale, washing out the clay fraction and sieving the fossil residues through a 0.125 mm screen. Specimens were picked under a microscope and recovered LAPs were identified using a JEOL JCM-7000 scanning electron microscope. Among the articulated specimens, we identified three genera: Strataster sp., n = 9 Furcaster sp. n = 6, Aganaster sp., n= 4, and indet = 1. In contrast, the microfossil (LAP) samples yielded seven genera: Umeriphora sp., rare, Strataster sp.,uncommon, Schonaster sp., common, Eugasterella sp., abundant, Vandelooaster sp., rare, Furcaster sp., rare, and Aganaster sp., common. The striking difference in diversity between the articulated specimens and the microfossil fraction suggests that a significant portion of ophiuroid diversity has been historically overlooked in the Paleozoic fossil record. We suggest that differences in relative abundances result from the much larger sample size in the LAP data.

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

doi: 10.1130/abs/2025AM-10124

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