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Keywords:

  • Azores;
  • last glaciation;
  • marine malacofauna;
  • mass extinctions;
  • Mollusca;
  • oceanic islands;
  • Pleistocene

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.