FOSSIL SIGMODONTINE RODENTS OF NORTHWESTERN ARGENTINA: TAXONOMY AND PALEOENVIRONMENTAL MEANING

P. E. ORTIZ; J. P. JAYAT; U. PARDIÑAS

Cenozoic Geology of the Central Andes of Argentina

INSTITUTO DEL CENOZOICO, UN de Salta (J..A. Salfity y R.A. Marquillas, eds.)

Lugar: Salta; Año: 2009;

Cricetid rodents of the Subfamily Sigmodontinae constitute one of the most diverse groups of extant New World mammals. Their fossil record in South America is restricted to the Early Pliocene-Holocene intervale. Recent findings in Northwestern Argentina have expanded the paleontological knowledge for this group, through several new localities from Middle-Upper Pleistocene to Upper Holocene. These findings have allowed to reconstruct the Quaternary paleoenvironmetal conditions in this region, mainly for the Late Pleistocene-Late Holocene interval. In three fossiliferous localities (La Angostura, Las Juntas, and Tafí del Valle) the presence of species very below their present altitudinal range indicates the descent of vegetational belts in these mountainous areas during Middle-Late Pleistocene. In these Pleistocene small mammal communities the species would have gone up and down following shifts and contraction of the vegetation belts. The oldest fossiliferous association, from La Angostura, constitutes a non-analogue assemblage by the altitudinal mixture of species that living today at different vegetational belts. The evidences indicate that the modern sigmodontine assemblages were settling down at the end of Pleistocene and that, with minor modifications, all the genera and species were already present in the area. Holocene sigmodontine assemblages do not show substantial distributional changes but rather it indicates variations in the relative abundance. These changes in relative abundance appears to be more related to the impact of human activities than climatic oscillations of the last centuries. Shifts from natural environments to agroecosystems restructured the small mammal communities causing loss of specific diversity.