Compositional variability of Pleistocene land snail assemblages preserved in a cinder cone volcano from Tenerife, Canary Islands

A Pleistocene land snail rich scoria sequence was studied to determine if it was influenced by taphonomic bias, climate change, or both, using a multifaceted approach that combines taphonomic, ecological, body size, and stable isotope data. Shell assemblages were sampled from two layers (Units A and B) in a cinder cone volcano of southern Tenerife (Canary Islands), dated to the glacial interval MIS 8 (~ 299-302 ka). The two units differed in taphonomy, species composition, and abundance, with the upper Unit B showing higher diversity, abundance, and lower alteration than the lower Unit A. Larger bodied species dominated Unit A and were better preserved than smaller species. These mismatches likely resulted from physical differences in the sediment matrix surrounding fossils, with larger scoria grains of Unit A enhancing destruction rates and thus favoring preservation of larger (more durable) taxa than smaller scoria grains of Unit B. Comparisons with modern assemblages from the coastal scrub, the plant biome in which the Pleistocene site currently resides, indicates that no modern analogue exists for these fossil assemblages within this biome. Shell oxygen isotope values reveal that the local climate was colder/wetter during MIS 8 than at present, which also may explain variations in species composition through time. These data suggest that both taphonomic and climatic factors appear to have induced temporal variations in taxonomic composition, but it is difficult to determine which of these has more significantly influenced the observed results.