Changes in the ranges of malacofauna elements in the territory of the Russian part of Eurasia in the Neopleistocene and Holocene under the influence of climatic factors
O.K. KLISHKO
Institute of Natural Resources, Ecology and Cryology, Siberian Branch, Russian Academy of Sciences, Chita, Russia
Keywords: Transbaikalia, Far East, mollusk shells, climatogenic succession, Pleistocene deposits
Abstract
The article presents information on the finds of shells of mollusks of the genera Monodacna, Unio, Lanceolaria, Planorbis, and Amuropaludina in the Pleistocene and Holocene deposits in Transbaikalia. Their shells are morphologically similar to those of modern species inhabiting regions of Russia that are geographically remote from Transbaikalia. Their ranges in the past were much more extensive than at present. The history of the existence and extinction of the species under discussion in Transbaikalia is reconstructed based on fossil finds and modern collections of mollusks. The ranges of the European species of the genera Monodacna, Unio, Planorbis, and the Far Eastern species of the genera Lanceolaria and Amuropaludina changed during the time period from the Pleistocene to the Holocene under the influence of climatic factors during the Ice Age. When comparing the absolute age of fossil shell finds or their host sediments with periods of warming and cooling on the regional geochronological scale, geochronological markers of the existence and extinction of the species under discussion in Transbaikalia were revealed. Thermophilic European species, widespread in the Pleistocene, became extinct in Eastern Siberia and Transbaikalia during the Ice Age, their ranges were interrupted and limited to the main part in Europe. The same scenario developed for the Far Eastern stenothermic species, which became extinct in Transbaikalia during the cold period of the Holocene. About 2-1,5 thousand years ago, their range, covering the entire Amur basin, was interrupted and limited to the main part in the Far East. The fact of habitation of local populations of European species of the common and wedge-shaped pearl mussel (Unio pictorum and U. tumidus) and the Far Eastern species of the Kian amuranodont (Amuranodonta kijaensis) in the refugium lakes of Transbaikalia has been noted. Changes associated with the natural cycles of cooling and warming in the Pleistocene and Holocene can be considered as a manifestation of climatogenic succession, during which the extinction of stenothermic species at the regional level and the rupture of ranges at the global level occurred.
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