Paleobiodiversity and Paleoecology Insights from a New MIS 5e Highstand Deposit on Santa Maria Island (Azores Archipelago, Portugal)

During the last two decades, the Macaronesian archipelagos have been the focus of multiple studies targeting the abundant and diversified fossil record from late Neogene and Quaternary deposits. This record of past biota, ecosystems and climates is crucial for understanding the impact of glacial–interglacial cycles on Atlantic littoral marine organisms. Coupled with ongoing studies on the factors responsible for global climate change and associated sea-level variations, they contributed decisively towards the development of the modern marine island biogeography theory. Our current knowledge of the evolutionary and biogeographic history of the past and extant, shallow-water marine organisms from the Macaronesian geographic region relies on detailed analysis of many individual fossiliferous outcrops by means of quantitative and qualitative methodologies. Here, we focus on the fossil record of a newly studied MIS 5e outcrop at Pedra-que-pica (PQP), on Santa Maria Island (Azores Archipelago, Portugal). This multidisciplinary work integrates geology, paleontology and biology, providing the first detailed description of the sedimentary facies and stratigraphic framework of the PQP MIS 5e sequence that, coupled with the documentation of the biodiversity and ecological composition of PQP molluscan assemblages, allows us to produce a paleoecological reconstruction and to compare PQP with other last interglacial outcrops from Santa Maria Island. Our results increase the number of the Azorean MIS 5e marine molluscs to 140 taxa (116 Gastropoda and 24 Bivalvia). <i>Ervilia castanea</i> (Montagu, 1803) is the most abundant bivalve, while <i>Bittium nanum</i> (Mayer, 1864) and <i>Melarhaphe neritoides</i> (Linnaeus, 1758) are the most abundant gastropod species. In addition, this work emphasizes the crucial importance of complementing quantitative collecting with qualitative surveys of the fossiliferous outcrops, because nearly 42% of the bivalve species and 28% of the gastropod taxa would be missed if only quantitative samples were used. Derivation of Hill numbers and rarefaction curves both indicate that the sampling effort should be increased at PQP. Thus, although Santa Maria Island is recognized by the scientific community as one of the best-studied islands regarding the last interglacial fossil record, this study emphasizes the need to continue with similar efforts in less known outcrops on the island.