TAPHONOMIC SIGNATURES IN DEAD SHELLS OF THE INVASIVE GASTROPOD RAPANA VENOSA (VALENCIENNES, 1846) AFTER TWO DECADES IN THE RÍO DE LA PLATA, URUGUAY

ABSTRACT: Rapana venosa (Valenciennes, 1846) is an invasive gastropod, the arrival of which in the Río de La Plata estuary 22 years ago is well-documented. Rapana venosa shells were collected during two sampling events from four beaches with different substrate types and wave energy regimes to compare the taphonomic attributes under different environmental conditions. We analyzed the samples by comparing frequencies of taphonomic attributes. Our results show that intermediate-reflective beaches with rocky substrates were dominated by intermediate- to highly fragmented specimens, with high corrasion, intermediate to high bioerosion, low bioencrustation, and medium to large sizes. In contrast, intermediate-dissipative beaches with sandy substrate, mobile stones, and occasional consolidated sediments were dominated by less fragmented shells, high to intermediate corrasion, scarcer bioerosion, low bioencrustation, and small- to medium-sized specimens. Results suggest that significant taphonomic differences arise within two decades under natural conditions. These findings imply that paleoenvironmental signals derived from the taphonomic attributes of fossil assemblages emerge much faster than the potential duration of time averaging of shelly fossils in shallow marine settings.