Los Alisos, a new fossiliferous locality for Guanaco Formation (late Miocene) in Jujuy (Argentina), and a first approach of its paleoecological and biochronology implications

摘要

Very scarce information is available about the extinct Neogene communities of the Subandean valleys of Jujuy province, Northwestern Argentina. A new vertebrate fossiliferous locality (Los Alisos), and the first mammalian assemblage from Guanaco Formation, is described. The taxa recorded include mainly caviomorph rodents (Hystricognathi) represented by Orthomyctera sp., Lagostomus sp., and an Octodontoidea and cingulates (Xenarthra) represented by the armadillos aff. Stenotatus, Dasypus sp. nov., two Euphractinae, and a Glyptodontidae. A single remain of a turtle (Testudines) is also described. The composition of the faunistic record has similitude with Andalhuala, Chiquimil and Salicas formations, but some taxa differ from all other late Miocene Northwestern Argentina localities. The most outstanding feature of Los Alisos paleocommunity is the presence of Dasypus, which confirms the existence of the genus in times as old as the late Miocene. The presence of a tuff with known age (5.9-6.4 Ma) immediately below to the fossiliferous level gives a lower temporal constraint for the association, and this absolute age as well as the biochrons of the identified taxa are compatible with an Huayquerian stage. The integrative analysis of the mammals of Los Alisos allowed preliminary paleoecological and paleoenvironmental inferences for Guanaco Formation, indicating a landscape composed by open areas, whether extensive or arranged in patches, including grasslands, under warm and seasonal climatic conditions.