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Mass extinctions in the Azores during the last glaciation: fact or myth?

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Abstract Aim 

The influence of the last glaciation on the shallow-water marine malacofauna of the Azores Islands is reviewed. We test, for this fauna, the ‘Pleistocene temperature theory’ of J.C. Briggs, which hypothesizes that a (supposed) lack of endemics in the older (Azorean endemic) fauna resulted from extinctions caused by a severe drop in sea surface temperatures during the Pleistocene. Location 

Santa Maria Island, Azores, Portugal. Methods 

We compare the fossil mollusc fauna of Prainha, Praia do Calhau and Lagoinhas Pleistocene outcrops with the recent mollusc fauna of the Azores Islands. We dated the fossil fauna, using shells of Patella aspera Röding, 1798, by standard U/Th methodology at the GEOTOP laboratory (Université du Québec à Montreal, Canada). Results 

Dating of the shells of P. aspera indicates that the deposition of the lower unit of the Prainha outcrop corresponded to Marine Oxygen Isotope Substage 5e (MISS 5e). Not a single endemic Azorean species of mollusc that is present in the Pleistocene fossil record has since become extinct, and we found no signs of ‘mass extinctions’ in the littoral marine molluscs of the Azores. The only species that were extirpated from these islands were thermophilic molluscs and littoral bivalves living in fine sand. Main conclusions 

Our results do not support Briggs’‘Pleistocene temperature theory’. Nor did we find evidence supporting the hypothesis that most of the marine organisms now present in the Azores recolonized the islands after the last glacial maximum.
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Keywords: Azores; Mollusca; Pleistocene; last glaciation; marine malacofauna; mass extinctions; oceanic islands

Document Type: Research Article

Affiliations: 1: MPB – Marine Palaeobiogeography Working Group of the University of the Azores, Azores, Portugal 2: Museo de la Naturaleza y el Hombre (Ciencias Naturales), Canary Islands, Spain 3: Departamento e Centro de Geologia, Faculdade de Ciências, Universidade de Lisboa, Lisboa, Portugal 4: GEOTOP – Université du Québec à Montréal (UQAM), Montréal, QC, Canada

Publication date: 2008-06-01

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