Resumen

VOGLINO, Damián  y  PARDINAS, Ulyses F. J.. Sigmodontine rodents (Mammalia: Rodentia: Cricetidae) and other micromammals from northern Buenos Aires province (Argentina): paleoenvironmental reconstruction for the uppermost Ensenadan. Ameghiniana [online]. 2005, vol.42, n.1, pp.143-158. ISSN 1851-8044.

We studied taxonomical and paleoenvironmental aspects of a micromammal assemblage recovered from Pleistocene sediments in Ramallo (33° 29' S, 60° 01' W, Ramallo county, Buenos Aires province). The bearing sediments can be referred to the uppermost part of the Ensenada Formation (Ensenadan Stage, Biozone of Tolypeutes pampaeus ) aged little younger than 0.78 Ma. The following sigmodontine rodents were recorded: Akodon cf. A. azarae (Fisch.), Necromys cf. N. benefactus (Thos.), Scapteromys cf. S. aquaticus - S. tumidus , Oligoryzomys cf. O. flavescens (Waterh.), Calomys cf. C. laucha - C. musculinus , Graomys cf. G. griseoflavus (Waterh.), Reithrodon auritus (Fisch.), and an unidentified genus. The Ramallo assemblage supports the hypothesis that the specific structure of modern sigmodontine fauna in Buenos Aires province was settled during the Ensenadan. An integral analysis including all the biotic evidences collected in the Ramallo section (rodents, marsupials, plant macrofossils, mollusks, and insects) indicates a transition from wet and warm conditions to dry and cold ones. The former conditions are suggested by the development of a Celtis tala Gill. ex Planch. wood, similar to those presently occurring in Ramallo area. The latter conditions are evidenced by the record of extralocal Central-Patagonian marmosines and rodents ( e.g. , Lestodelphys sp., Microcavia sp.) and the absence of C . tala . This environmental and climatic change took place above the Matuyama-Brunhes boundary, at the end of the Ensenadan stage, indicating a delay between the paleomagnetic reversion and the environmental deterioration in northeastern Buenos Aires province.

Palabras clave : Argentina; Pleistocene; Límite Matuyama-Brunhes; Sigmodontinae; Taxonomy; Paleoenvironments.