54-10 Elements of the modern molluscan fauna in the Plio-Pleistocene of the southeastern United States: Taxonomic practice or persistence?

Session: New Approaches to Old Fossil Collections

Presenting Author:

Authors:

Abstract:

For over 200 years, paleontologists have applied the names of extant molluscan species to geologically young fossil material from the southeastern United States. This study system provides critical data about the evolutionary history of the modern gastropod and bivalve fauna of this region, which is today represented by over 2000 species based on a new analysis of GBIF data. While some extant species have long durations that extend back millions of years into the Pliocene and even Miocene, it is also likely that some names of extant taxa have been applied to fossil material in lieu of comprehensive monographic treatments of individual stratigraphic units. We explore the fossil record of extant species in this system using a taxonomically standardized, specimen-based dataset derived from the collections of the Florida Museum of Natural History. The complete fossil dataset contains nearly 123,000 occurrence records for almost 2,700 species of marine bivalves and gastropods, approximately a third of which are purportedly extant. Using a subset of these data, we compare Lyellian percentages for successively younger stratigraphic units in Virginia and North Carolina versus comparable units in southern Florida. Predictably, Lyellian percentages increase in successively younger units in both sequences but are higher in Late Pliocene and Early Pleistocene units in southern Florida than in the north. We ascribe this result in part to workers sometimes applying names of extant species to fossil material when monographs are not otherwise available. However, another possibility is that the southern end of the fauna was less impacted by Plio-Pleistocene climatic changes and had lower rates of extinction. This study informs our understanding of the timing and sequence of the modernization of the modern western Atlantic molluscan fauna and emphasizes that museum collections are critical to this research. This material is based upon work supported by the National Science Foundation under grant numbers 2525946 and 2225013.

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

doi: 10.1130/abs/2025AM-7368

© Copyright 2025 The Geological Society of America (GSA), all rights reserved.