Mammals of the Tarija Valley (Southern Bolivia): diversity, endemism and the problem with its antiquity

SOIBELZON, E.; RODRIGUES BUALÓ, S.; AVILLA, L.; SOIBELZON, L.H.; ZURITA, A.

Las Vegas

Congreso; 71st Annual Meeting SVP; 2011

Tarija Valley is located in southern Bolivia, 140 km north from the border with Argentina. During the last 400 years, several paleontological expeditions worked there but, unfortunately, most of the collected fossils lack precise stratigraphic and geographic provenance. However they were used to establish chronologies and correlations with the Pampean Region (?PR?, Argentina). The fossiliferous units were referred either to Early and/or Middle Pleistocene (Ensenadan and Bonaerian PR stages respectively), and to the Late Pleistocene-Early Holocene (Lujanian PR stage). More than 90 taxa were reported, many of them considered as endemic. We present here the preliminary results of a taxonomic revision (including new fossils remains collected during our field work) and analyze the diversity and probably age of Tarija mammals. We proposed that: 1-respect to the endemic species published, at least four are not endemic (Megatherium tarijense, Scelidodon tarijense, Arctotherium tarijense, A. wingei), since they are registered in the PR too; 2-in Tarija there is a high frequency of pampatherids, gomphotherids, equids, hydrochoerids and tapirs, and a low taxonomic diversity of glyptodonts and tayassuids, compared with the PR; 3-two species are distributed exclusively in the Ensenadan of the PR (Glyptodon munizi and Arctotherium angustidens), were recorded at Tarija. According to recent published data, the fossiliferous levels are located at the upper part of the sequence, which were deposited during Late Pleistocene, this implies a local survival of these species; 4-the lack of stratigraphic information of the previously collected fossils, prevent us to assume that every remain comes from the upper levels of the Tarija sequence; 5-some faunal elements (Hydrocheridae, Tapiridae) suggest a predominance of wet and warm environment, in contrast with that proposed for the PR. Finally, we took samples of volcanic ash and sediment (associated with well identified fossil remains) to dating. This study is part of a cooperation project between ?Museo Nacional Paleontológico-Arqueológico de Tarija? (Bolivia) and the ?Universidad Nacional de La Plata? (Argentina).