Faunistic changes between the Middle/Late Pleistocene and the Holocene on the Atlantic coast of Tierra del Fuego: molluscan evidence

The marine terraces located on the atlantic coast of Tierra del Fuego (Argentina) were previously assigned to different sea-level highstands from the Middle Pleistocene to the Holocene. This study is focused on the analysis of the mollusc assemblages recovered from those terraces. When comparing Middle/Late Pleistocene mollusc assemblages with adjacent Holocene/modern ones, ecological changes in the fauna were recognized. The Pleistocene assemblages are less diverse and are dominated by infaunal bivalves, whereas Holocene and modern assemblages are more diverse and are dominated by epifaunal taxa, with a higher presence of gastropods. However, on a biogeographic scale, the fact that Pleistocene taxa (with the probable exception of Retrotapes sp.) are living today in the region is attributed to the location of the study sites, at the centre of the Magellan biogeographic unit, with species far away from the edges of their ranges of distribution. Regional faunistic changes and the local disappearance of Retrotapes in post-glacial benthic communities in the area are therefore interpreted on the basis of regional and local causes, most probably associated to substrate changes, and not on a global trend related to large-scale patterns.