FIRST SMALL MAMMALS ASSEMBLAGE (DIDELPHIMORPHIA AND RODENTIA) FROM UPPER PLIOCENE IN NORTHWESTERN ARGENTINA

P. E. ORTIZ; M. J. BABOT; P. JAYAT; U. F. J. PARDIÑAS; D. GARCÍA LÓPEZ

Mendoza

Congreso; Xth International Mammalogical Congress; 2009

Sociedad Argentina para el Estudio de los Mamíferos

Small mammals record for Pliocene in Northwestern Argentina is scarce. In this region, the period is mainly represented by the Uquía Formation, mostly characterized by medium and large mammals (e.g., Gomphotheriidae, Equidae, Tayassuidae, Megatheriidae, Glyptodontidae, and Dasypodidae) that document the GABI. We describe the first fossil assemblage of small mammals for Pliocene times in Northwestern Argentina. The remains were found in the middle unit of Uquía Formation (ca. between 3.0 and 2.5 Ma), corresponding to the Marplatan stage, in San Roque, near Humahuaca, Jujuy province. The assemblage is constituted by 32 individuals belonging to 9 species: didelphimorph marsupials (Thylamys sp. and Didelphimorphia indet.), sigmodontine rodents (Akodon cf. A. albiventer, Necromys cf. N. amoenus, Auliscomys cf. A. sublimis, Auliscomys sp., and an innominate Phyllotini), and caviomorph rodents (Octodontidae indet. and Ctenomys sp.). The sample is dominated by the undescribed phyllotine, represented by many mandibles and fragments of maxillae with molar series, constituting more than 90% of the recorded specimens. These specimens show morphological affinities with the nowadays widespread Calomys and Eligmodontia, but some cranial (short incisive foramina), mandibular (short masseteric crest) and dental characters (conspicuous second minor fold in M1-M2) indicate that they pertain to a new genus. Akodon albiventer, Necromys amoenus and Auliscomys sublimis are today conspicuous elements of the small mammals communities in high altitude Andean region of northwestern Argentina and southwestern Bolivia. These species characterize open environments with rocky outcrops in Puna and High Andean eco-regions. Moreover, the record of the Octodontidae indet. supports the idea of an arid or semiarid environment. This report constitutes the first mention in the fossil record for taxa assignable to N. amoenus, and the oldest record for specimens that can be referred to A. sublimis and A. albiventer.