TAPHONOMIC IMPLICATIONS OF LAND CRAB PREDATION OF SNAILS ON SAN SALVADOR ISLAND, BAHAMAS

Fossilized Cerion land snails of the West Indies can provide important paleoenvironmental and paleoecological information. Cerion body size and morphology vary considerably both spatially and temporally. Some published studies have explored environmental forcings such as coastal wind exposure as a potential driver of morphology. However, land snails do have predators, and the influence of predation on the fossil record of Cerion should not be overlooked. This work aims to explore 1) how prey selection among land crabs may influence the size of fossil Cerion, and 2) possible crab predation signatures that may be applied to analyses of fossil Cerion. Three species of Bahamian land crabs (Gercarcinus lateralis, Ucides cordates, Cardisoma guanhumi) were offered a choice of 5 snails (1 Hemitrochus variens, 2 small Cerion, 2 large Cerion) for 13 days under laboratory control. 195 kills and 6 failed attacks were recorded, and the remaining shell fragments were analyzed. Chi-squared analyses show that all crabs, regardless of their ability to kill large Cerion, killed smaller snails preferentially. Killed snail remains were characterized by high levels of fragmentation and rare preservation of crab predation traces. However, failed attacks had distinctive predatory signatures such as claw holes and lip removal. Moreover, the protoconch was more likely to be preserved after a successful crab attack than either the body chamber or the aperture. These findings indicate that land crab predation may be underestimated in the fossil record and that larger Cerion shells may be preferentially preserved. Furthermore, temporal and spatial fluctuations in Cerion size may partly be attributed to varying intensities of size selective predation by land crabs.