Biodiversity change and extinction risk in Plio-Pleistocene Mediterranean bivalves: the families Veneridae, Pectinidae and Lucinidae Silvia Danise 1 * and Stefano Dominici 2 1 Dipartimento di Scienze della Terra, Università degli Studi di Firenze, Firenze 50121, Italy 2 Museo di Storia Naturale, Università degli Studi di Firenze, Firenze 50134, Italy *Correspondence: silvia.danise@unifi.it Abstract: Understanding species vulnerability to extinction is one of the goals of conservation. Here we ana- lyse a dataset of Plio-Pleistocene Mediterranean bivalve occurrences (families Veneridae, Pectinidae and Luci- nidae), to reconstruct biodiversity change through time, and to test whether species occurrence frequency, geographical range and habitat specialization explained species survival or extinction. We found that biodiver- sity loss started soon after the mid-Piacenzian warming Period, at c. 3.0 Ma, and continued as climate progres- sively cooled, up to the Gelasian. It was more gradual than expected, as some species found a temporary refugium in the warmer, eastern Mediterranean. Extinction was more intense for the epifaunal, mobile pectinids, compared to the infaunal, siphonate venerids and lucinids. Occurrence frequency, geographical range and hab- itat specialization were good predictors of species extinction for the Veneridae and the Lucinidae. For the Pec- tinidae habitat specialization was a good predictor of extinction, but not occurrence frequency and geographical range, as also some common and geographical widespread Pliocene species became extinct. In this family, extinction risk was better predicted by latitudinal range than geographical range. Habitat loss due to the frag- mentation of carbonate palaeoenvironments and high metabolic rates related to large body size also played a role in pectinid extinction. Supplementary material: Supplementary Figure, Tables and the analysed dataset are available at https://doi. org/10.6084/m9.figshare.c.6223137 More than 17 000 marine species have been reported from the Mediterranean Sea which, despite its small dimensions (0.82% of the ocean surface), hosts more than 7.5% of global marine known biodiversity (Bianchi and Morri 2000), and it is thus considered a biodiversity hotspot, characterized by elevated endemism (Coll et al. 2010). It is known to palaeon- tologists, however, that such biodiversity was higher than today in the early history of the basin (i.e. since the repopulation of the basin after the Messinian salinity crisis, around 5.3 million years ago, Ma), and this is known mainly thanks to the study of hard-shelled macro-invertebrates, especially mol- luscs (Monegatti and Raffi 2001). Molluscs are also the most species-rich phyla inhabiting Mediter- ranean waters today, from brackish lagoons to bath- yal depths, with more than 2000 molluscan species identified (Zenetos et al. 2002). As such, reconstruct- ing their diversity through time, and understanding causes of biodiversity loss, can give important insights on adaptation of marine species to climate and environmental change and their vulnerability to extinction. The Italian Peninsula has the most stratigraphi- cally extended and complete outcrops of Pliocene (Zanclean–Piacenzian, 5.33–2.58 Ma) and early Pleistocene (Gelasian–Calabrian, 2.58–0.77 Ma) marine sediments of the entire Mediterranean area, with sedimentary facies that span from shelf to bath- yal settings (Dominici et al. 2020b) exposed due to the elevated uplift rates of the main mountain ranges (e.g. Schiattarella et al. 2006; San Jose et al. 2020). The sediments are extremely fossiliferous, their mol- lusc content has been studied since the dawn of palaeobiology (e.g. Brocchi 1814; see Dominici and Scarponi 2020), and they have been the object of intense taxonomical and palaeoecological studies over the last two centuries. It is not surprising then, that the first attempts to quantify past changes in mollusc biodiversity in the Mediterranean Sea were based on the Italian fossil record (Raffi et al. 1985; Raffi and Monegatti 1993; Monegatti and Raffi 2001), and that the faunistic units established in these works (Mediterranean Pliocene Molluscan Units, MPMUs), and their chronostratigraphical sig- nificance, are still applied to the entire Mediterranean area and the neighbouring Atlantic (e.g. da Silva et al. 2010; Benyoucef et al. 2021). According to these studies, Mediterranean molluscs experienced a strong biodiversity loss since the Pliocene; detailed From: Nawrot, R., Dominici, S., Tomašových, A. and Zuschin, M. (eds) Conservation Palaeobiology of Marine Ecosystems. Geological Society, London, Special Publications, 529, https://doi.org/10.1144/SP529-2022-44 © 2022 The Author(s). Published by The Geological Society of London. All rights reserved. For permissions: http://www.geolsoc.org.uk/permissions. Publishing disclaimer: www.geolsoc.org.uk/pub_ethics Downloaded from https://www.lyellcollection.org by Silvia Danise on Dec 16, 2022