Late Pleistocene sigmodontines (Mammalia : Rodentia)from the Tafi valley (Tucuman, Argentina): Taxonomy, taphonomy and paleoenvironmental reconstruction

LATE PLEISTOCENE SIGMODONTINES (MAMMALIA: RODENTIA) FROM THE TAFI VALLEY (T UCUMAN, ARGENTINA): TAXONOMY, TAPHONOMY AND PALEOENVIRONMENTAL RECONSTRUCTI ON. An exceptionally rich rodent assemblage of Lujanian age (latest Pleisto cene) at La Angostura (26 degrees 55' 30" S, 65 degrees 41' 50" W, Tafi val ley, Tucuman province; 1900 m above sea level) provides the first evidence of sigmodontine rodents in the fossil record of northwestern Argentina. Ide ntified taxa are: Abrothrix illuteus Thomas, Akodon sp., Necromys cf. N. la ctens (Thomas), Oxymycterus cf. O, paramensis Thomas, Oligoryzomys cf. O. f lavescens (Waterhouse), Oligoryzomys cf. O. "longicaudatus" (Bennett), Andi nomys edax Thomas, Calomys cf. C. laucha C. musculinus, Neotomys ebriosus T homas, Phyllotis sp., Reithrodon auritus (Fischer), and dagger Tafimys powe lli Ortiz et al. These include the first fossils of the genera Neotomys Tho mas and Andinomys Thomas in Argentina. Taphonomic analysis indicates that t he assemblage is a fossil owl pellet accumulation. Consequently, it can be assumed to be a biased representation of the small mammal fauna of a relati vely small area over a relatively brief time span. This association has no modern analogue because today these species live at different altitudinal v egetation belts. The fauna indicates a community from the high-altitude gra ssland ecotone, with elements of the Yungas, Puna and High Andeans. Tempera tures may have been lower than today. Although the species composition is s imilar to the modem sigmodontine community in the area, quantitative variat ions in proportional representation can be attributed to Holocene climatic conditions and, probably, to the impact of human populations in historical times.