TAPHONOMIC TRENDS IN LIVE, DEAD, AND FOSSIL GASTROPOD ASSEMBLAGES FROM FLORIDA SPRINGS AND RIVERS

Florida freshwater springs and rivers are increasingly threatened by anthropogenic and climate-related threats including introduced species, rising sea levels, and habitat destruction. In these springs and rivers, molluscan shell accumulations provide a record of ecological, environmental, and biological changes. However, taphonomic processes, which form and shape these assemblages, are relatively understudied in rivers and springs, limiting our understanding of their informative value for paleontological and conservation research. Our study explores the taphonomic processes affecting live (living gastropods), death (loose, surficial shell accumulations), and fossil (late Pleistocene–early Holocene in situ sediments) molluscan assemblages, sampled from the Silver, Ocklawaha, and Wakulla Rivers in Florida. The taphonomic condition of six traits (aperture damage, body damage, external color, abrasion, juvenile spire condition, and exterior luster) were recorded in 2,731 specimens of four gastropod species: Pomacea paludosa (n=409), Callinina georgiana (n=899), Planorbella trivolvis (n=593), and Planorbella duryi (n=830). Taphonomic trait values were combined into a Total Taphonomic Score (TTS) for each specimen.

Death assemblage specimens show, on average, the highest TTS (1.13), reflecting greater taphonomic alteration than fossil (0.07) and live (-8.64) specimens. They also show the greatest range in scores (-9.06 to 7.48) compared to their fossil (-8.78 to 7.48) and live (-11.62 to -7.01) counterparts. These results agree with previous research suggesting that death assemblages are likely formed by a combination of inputs from recently dead and reworked fossil material, though the species in this study may undergo additional alteration when reintroduced to death assemblages. Scores of fossil specimens from the Wakulla and Silver Rivers show similar means and ranges, but specimens from the Ocklawaha River lack the low to moderately altered individuals seen in the other two rivers. Additionally, fossil specimens of all species show similar scores, suggesting similar taphonomic pathways for all examined taxa. These results indicate death assemblages are complex in origin, and their taphonomic histories must be considered before using them to assess long-term ecological change.