Ecological fidelity of Pleistocene-Holocene land snail shell assemblages preserved in carbonate-rich paleosols

Studies that assess the ecological fidelity--preservation of the original community--of terrestrial shell accumulations are uncommon but essential to infer accurate changes in past ecosystems. When live-dead comparisons are unavailable, the taxonomic agreement between differing taphofacies may be used to evaluate the fidelity of ancient shelly assemblages. This approach was used to approximate the fidelity of Quaternary land snails preserved in carbonate-rich paleosols from the northeastern islets of the Canary Archipelago. Such macroscopic alteration as fragmentation, corrosion, carbonate coating, and color loss affected shells, however, microscopic analyses concluded substantial diagenetic alterations unlikely. The shell abundance negatively correlated with fragmentation, suggesting that a higher proportion of shells may be a consequence of higher shell input rate and lower shell destruction rate rather than lower sedimentation rate, as predicted by taphonomic models. Strongly and weakly altered taphofacies significantly differed in species abundances. Substantial taphonomic bias was improbable, however, because both taphofacies contained taxa with comparable durability. Temporal fluctuations in taphonomy and ecology suggest variable environmental conditions operated through time. The overall decline in shell abundance from the last glacial to interglacial paleosols may be explained by a decline in humidity and reduced island surface area resulting in lowered snail proliferation, and in turn, a decreased net shell input rate. This study emphasizes that the original community is preserved within the studied terrestrial shell accumulations regardless of the degree of taphonomic alteration. Measures of past taxonomic richness and diversity, therefore, may be used as a reliable measure of the original snail community.