MAMMALS OF THE TARIJA VALLEY (SOUTHERN BOLIVIA): DIVERSITY, ENDEMISM AND THE PROBLEM WITH ITS ANTIQUITY

SOIBELZON, E.; RODRIGUEZ-BUALÓ, S.; AVILLA, L.; SOIBELZON, L; ZURITA, A. E

Las Vegas

Congreso; Annual Meeting of the SVP; 2011

SVP

The Tarija Valley is located in southern Bolivia, 140 km north of 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, the fossils 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 fossil remains collected during our field work) and analyze the diversity and probable age of the Tarija mammals. We proposed that: (1) with 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 that are distributed exclusively in the Ensenadan of the PR (Glyptodon munizi and Arctotherium angustidens) are also recorded at Tarija. According to recently published data, the fossiliferous levels are located at the upper part of the sequence, which was deposited during the Late Pleistocene, this implies a local survival of these species; (4) the lack of stratigraphic information for the previously collected fossils prevents us from assuming that every specimen comes from the upper levels of the Tarija sequence; and (5) some faunal elements (Hydrocheridae, Tapiridae) suggest a predominance of wet and warm environments, in contrast with that proposed for the PR. Finally, we took samples of volcanic ash and sediment (associated with well identified fossil remains) for dating.