189-24 Skulls by the Seashore: New Specimens of Cynomys with Insights into the Taphonomy of Late Pleistocene Fossils Found on McFaddin Beach, Texas.

Session: Paleontology, Paleoecology/Taphonomy (Posters)

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Abstract:

Fossils from McFaddin Beach, Texas, document a diverse vertebrate fauna that inhabited a broad continental shelf and adjacent marine environments during the Late Pleistocene. The fossils that accumulate along 32 km of McFaddin Beach in Jefferson County, Texas, are hypothesized to originate from intact, terrestrial deposits on the now submerged continental shelf. The fossils are often significantly modified by taphonomic processes. Those processes favor dense, durable elements including megafauna teeth, influencing our perspective of Late Pleistocene biodiversity on the continental shelf. Smaller, more fragile elements are rarely preserved, but include two skulls of rodents described here. Both skulls are filled and encased or covered with a dense, fine-grained rock matrix. Polished, rounded, and abraded surfaces on both specimens suggest a history of transport by ocean currents. SHSU-1-948 is a largely complete skull missing the parietals, supraoccipital, and the anterior portions of the nasals and premaxilla. SHSU-1-1048 is an incomplete skull preserved in rock matrix with only portions of the dentition and orbits visible externally. High-resolution CT imaging of SHSU-1-1048 revealed the posterior portions of the premaxilla, maxilla with teeth, and portions of the palatine and presphenoid. Both skulls are three-dimensionally preserved with delicate and taxonomically informative structures still present. The overall morphology of SHSU-1-948 is intact, with the outline of the orbits, portions of the masseteric tubercle, and the crowns of multiple cheek teeth. The roots of P4-M3 are preserved in SHSU-1-1048, as is the left optic canal, choanae, posterior maxillary foramina, and even a portion of the cribiform plate of the ethmoid. The size and form of the cheek tooth crowns and roots, combined with other structures, support the assignment of both specimens to the prairie dog genus Cynomys. The preservation suggests a sequence of taphonomic events beginning with post-mortem burial, followed by lithification within intact submerged Pleistocene deposits, and, eventually, exhumation. Transport by ocean currents may be prolonged, potentially involving intermediate episodes of re-deposition before reaching the shore. Accordingly, the prairie dog fossils highlight that the geochemical processes behind lithification and cementation occurring in the Gulf of Mexico are likely critical to the preservation and discovery of fossils from McFaddin Beach.

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

doi: 10.1130/abs/2025AM-10926

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