Fossil sigmodontine rodents of Northwestern Argentina: Taxonomy and paleoenvironmental meaning

ORTIZ, P.; JAYAT, P.; PARDIÑAS, U.F.J.

Cenozoic Geology of the Central Andes of Argentina

SCS Publisher

Año: 2011; p. 301 - 315

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 interval. Recent findings in northwestern Argentina have expanded the paleontological knowledge of this group through several new localities from middle-late Pleistocene to late Holocene. These findings have allowed reconstruction of 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 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 species would have gone up and down following shifts and contraction of the vegetation belts. The oldest fossiliferous association -La Angostura- constitutes a non-analogue assemblage due to the altitudinal mixture of species living today at different vegetational belts. Evidence indicates that the modern sigmodontine assemblages were settling down at the end of Pleistocene and that all the genera and species were already present in the area with minor modifications. Holocene sigmodontine assemblages do not show substantial distributional changes but rather indicate variations in relative abundance. Changes in relative abundance appear to be related more 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.