Abstract

MIQUEL, Sergio E.  and  BELLOSI, Eduardo S.. Middle eocene land Microgastropods (Charopidae) from Gran Barranca (Central Patagonia, Argentina). Ameghiniana [online]. 2007, vol.44, n.1, pp.121-131. ISSN 1851-8044.

New land microgastropods Charopidae were found in the Rosado carbonate paleosol (late Middle Eocene, Mustersan South American Land Mammal Age), of the Sarmiento Formation at the Gran Barranca locality (Chubut province, Argentina). The most ancient fossils of Rotadiscus and Lilloiconcha and the first Eocene record of Radiodiscus are described. Most of the fossil taxa are compared with extant species (Rotadiscus amancaezensis (Hidalgo), Stephadiscus celinae (Hylton Scott), Radiodiscus riochicoensis Crawford and Lilloiconcha gordurasensis (Thiele)), and hence they would be their first fossil record. The high diversity of the assemblage (7 species) is unusual for a single bed, and it is comparable to the more diverse recent South American microgastropod faunas. The gastropod assemblage of the Rosado paleosol is similar to present-day northwestern Patagonia association, and indicates a humid and cold-temperate climate. Such conditions would have change during the late pedogenesis stage (Late Eocene) towards a dry climate. The abundance of the specimens and the preservation of their delicate sculptures reflect appropriate conditions for preservation related to soil carbonate cementation.

Keywords : Microgastropods; Charopidae; Eocene; Patagonia; Gran Barranca; Sarmiento Formation.