Persististrombus coronatus (Mollusca: Strombidae) in the lower Pliocene of Santa Maria Island (Azores, NE Atlantic): Paleoecology, paleoclimatology and paleobiogeographic implications

Abstract

The family Strombidae is one of the twenty-three families and subfamilies of gastropods associated with tropical environmental conditions, and therefore useful as a biogeographical and paleoclimatic proxy. Today, the strombid genus Persististrombus is represented in the NE Atlantic by a single species restricted to the tropical Mauritanian–Senegalese Province. This work reports the occurrence of Persististrombus coronatus from the lower Pliocene of Santa Maria Island in the Azores Archipelago. Based on this occurrence, and on the Mio-Pliocene fossil record of the NE Atlantic oceanic islands, paleoclimatological considerations are discussed, which allow, for the first time, to include the Azores and the other Macaronesian islands in a wider context of the NE Atlantic paleobiogeographical molluscan provinces. Late Miocene to present day molluscan biogeographic units, ranging in latitude from 60°N down to 17°S, are here defined and the boundaries of the proposed climatic zones are outlined. We suggest that during the upper Miocene–lower Pliocene, the paleoclimate at Santa Maria Island was drastically different from that seen at those latitudes today, with mean annual sea surface temperatures (SSTs) about 3.7°C to 6.3°C higher than the present-day 20.6°C, and with mean monthly SSTs ranging from 20°C to 28°C, with six months with mean SSTs over 24°C, conditions typical of a tropical setting.