A new record of gastropods in the Miocene of South Bohemia (České Budějovice Basin)

 

Eva Kadlecová, Vladimír Kocura

Geoscience Research Reports 49, 2016, pages 191–194
Map sheets: Bechyně (22-42)

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Published online: 30 September 2016

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Abstract

Mostly fragmentary fossil material of the freshwater gastropods was found in the exposure of the Mydlovary Formation (Neogene, Miocene, upper Burdigalian - lower Serravallian) near Týn nad Vltavou, on the northern periphery of the České Budějovice Basin (Southern Bohemia) north of Bohunice nad Vltavou. The four species of the Family Planorbidae - Gyraulus sp. and Gyraulus dealbatus (Braun in Walchner), Planorbarius sp. and Planorbarius cornu (Brongniart) and the four species of the Family Lymnaeidae - Radix sp., Radix subovata (von Zieten) and Radix vel Stagnicola sp. and Stagnicola subpalustris (Thomä) were recognized. Composition of the poor association indicates fluviatile or lacustrine conditions and its size distribution probably reflects unfavourable taphonomic processes (a destruction of small shells both by their dissolution and crushing during the sandy sediment compaction). Only several specimens of undeterminable terrestrial (helicid) gastropods were gathered from this exclusively freshwater association. This gastropod association is somewhat unique within the České Budějovice Basin. The only comparable fauna composition was found in the nearby Třeboň Basin by Čtyroký and Fejfar (1962). In the newly described fauna from Bohunice, the mostly slack-water taxa are present: representatives of the genus Stagnicola are typical for floodplains and peaty temporary small lakes. Genus Radix prefers waters with muddy or stony ground, near banks of river or small lakes. The most abundant taxa among this association are planorbids, genera Gyraulus and Planorbarius. Representatives of these two genera could live in both lentic and locid waters; Gyraulus could withstand short drought. It is probable, that the fossil- rich sands were deposited in the area of floodplain meadow and/or temporarily flooded area alongside the river banks.