By Sergio Martínez, Claudia J. del Río, Alejandra Rojas
The Quaternary contains a short time within the Earth’s heritage, and except a number of exceptions, molluscan assemblages recovered from exposures alongside the coast of Southwestern South the USA (Southern Brazil, Uruguay, Argentina) are basically an analogous than those who inhabit the quarter at the present time, resulting in the idea that no vital swap within the distribution of the faunas considering the fact that Pleistocene occasions has happened. notwithstanding, the great taxonomic and temporal solution reached within the final years, allowed us to notice a few biogeographic adjustments, even if conventional biogeographic devices stay a similar (i.e. Magellanic and Argentinean Provinces). those differences contain almost always diversifications within the taxonomic composition of the assemblages and within the southern obstacles of a few species distributions (extralimital species), at the present time retracted northwards. those adjustments are regarding southward shifts of the nice and cozy waters of the Brazilian present, correlated with worldwide hot peaks. This phenomenon was once extra severe within the overdue Pleistocene (MIS 5e) and within the Holocene among ca. 6500-3500 14C 12 months.
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According to the present geographical ranges of the studied species, temperatures were warmer during the Quaternary than during Recent times, but no significant temperature differences are recorded between the Pleistocene and Holocene assemblages. More fine-tuning works are needed to elucidate whether the paleoclimatic information provided by molluskan faunas reflects the same results that could be reached through the studies of other taxonomic groups or using different methodologies. There is an important verification: the areas located in the extremes of the geographical distribution of species have not extralimital species.
Although there are some methodological problems for testing this latitudinal richness variation during the Quaternary of the Southwestern Atlantic region, the multivariate analyses carried out show a latitudinal control both for the Pleistocene and Holocene assemblages, grouping the areas according to their geographical location. Richness and taxonomic diversity do not fully confirm this pattern in the region during Quaternary times and, even when Tierra del Fuego shows the lowest richness, it must be kept in mind that this southern region of the Southwestern Atlantic is one of the less studied, and that future findings could substantially increase the number of recorded taxa.
Biogeography of the Quaternary Molluscs of the Southwestern Atlantic Ocean by Sergio Martínez, Claudia J. del Río, Alejandra Rojas