The mesogastropod Littorina littorea (Linné, 1758) in Iceland: palaeobiogeography and migration

At present, the periwinkle, Littorina littorea (Linné, 1758), is not found living in Iceland. The only confirmed occurrence of the species in Icelandic sediments is in the Middle Pleistocene upper littoral conglomerate at Búlandshöfdi, Snaefellsnes, West Iceland. These layers were deposited during an interglacial stage, slightly older than 1.1 Ma. The species apparently evolved from the Pacific L. squalida Broderip & Sowerby, 1829, after the trans-Arctic/North Atlantic migration from the Pacific, possibly in response to cooling and increasing environmental energy. The oldest fossil occurrence of L. littorea is in the British Red Crag Formation, between 2.55 and 2.4 Ma; it is unknown from the Pliocene Tjörnes deposits in N Iceland, older than 2.6 Ma. This indicates that the species separation postdates the deposition of the uppermost Serripes Zone of Tjörnes, after the tide of the migration wave passed Iceland, but before it reached the North Sea area and Britain, between 2.6 and 2.4 Ma. The taxonomic diversity and palaeobiogeography of North Atlantic molluscs were greatly affected by the major climatic changes that resulted in an extensive glaciation at about 2.5 Ma.