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Minimum radiocarbon ages of marine Pleistocene molluscs from Uruguay range from 29,500±600 to 35,500±1900 14C yr B.P. Because knowledge of the marine Quaternary stratigraphy of Uruguay remains inadequate, no attempt is made to correlate between these deposits and recognized lithostratigraphic units. Analysis of the temperature and salinity ranges of the various molluscs suggests the establishment of a poly-euhaline fauna that inhabited waters warmer than present at the same latitude. This is supported by a northward retreat in the recent distribution of Chrysallida cf. C. gemmulosa, Nioche subrostrata, and probably Anomalocardia brasiliana. These marine Pleistocene deposits can probably be correlated with the last interglaciation (oxygen-isotopic substage 5e). At that time the fluvial-marine front of the Rio de la Plata was displaced much further northwestward than previously supposed. Chrysallida cf. C. gemmulosa and Limaria sp. are recorded in Uruguayan Quaternary deposits for the first time.

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RESUMO -É apresentada a descrição das estruturas bioerosivas registradas em conchas de moluscos marinhos da Formação Villa Soriano (Pleistoceno superior-Holoceno), Uruguai, bem como a análise dos parâmetros paleoecológicos dominantes durante a deposição. É verificada a preferência dos gastrópodos predadores por determinados sítios de perfuração nas conchas dos bivalvos. Foram identificados três icnogêneros: Entobia Bronn, 1838, Caulostrepsis Clarke, 1908 e Oichnus Bromley, 1981. Entobia indica a presença de esponjas cliônidas e Caulostrepsis a ocorrência de poliquetos perfuradores. Entobia indica, ainda, águas límpidas livres de sedimentos em suspensão. Por outro lado, Oichnus indica a predação por parte de gastrópodos sobre bivalvos e outros gastrópodos. O centro da concha de Ostrea equestris é o sítio preferido pelos predadores. Devido à posição de vida da espécie, a valva direita é a mais perfurada. Os gastrópodos mais prováveis como predadores de bivalvos de fundos duros são: Urosalpinx cala, U. haneti e Thais haemastoma. Já o predador mais provável dos bivalvos de fundos moles é Natica isabelleana. ABSTRACT -BIOEROSION STRUCTURES ON MARINE MOLLUSCS FROM THE VILLA SORIANO FORMATION (LATE PLEISTOCENE-HOLOCENE) OF URUGUAY. Bioerosion structures found on marinemolluscs of the Villa Soriano Formation (late Pleistocene-Holocene) of Uruguay are described, and the main paleoenvironmental parameters dominant during the depositional events are analyzed. The preference of the drilling site on the shell of the prey bivalves by predator gastropods is verified. Three ichnogenera were found: Entobia Bronn, 1838, Caulostrepsis Clarke, 1908 and Oichnus Bromley, 1981. Entobia records the presence of clionid sponges and Caulostrepsis the presence of boring polychaetes. Entobia is also an indicator of clean waters. On the other hand, Oichnus records the predation of gastropods on bivalves and other gastropods. The preferred site of the shell of Ostrea equestris by the predators is the center of the shell, and drills are more common on right valves, due to the life position of this species. Probable species of predators are Urosalpinx cala, U. haneti and Thais haemastoma on hard substrate prey species and Natica isabelleana on soft substrate prey species.