Extinction of a gomphothere population from Southeastern Brazil: Taphonomic, paleoecological and chronological remarks

摘要

During the Quaternary in South America, the gomphotheres were one of the most common elements in the mammal megafauna. They went extinct in an evolutionary event known as the Late-Pleistocene Megafaunal Extinction, of which climate changes and human hunting are commonly claimed as the main possible causes. Most of the Brazilian Pleistocene fossil mammals did not preserve collagen, so alternative dating techniques are needed. In this case, the only option for dating such fossils is via Electron Spin Resonance (ESR) dating. The aim of this paper is (ⅰ) to place the Quaternary Aguas de Araxa's Notiomastodon platensis population in a chronological context through ESR dating and, (ⅱ) to investigate its paleoenvironmental context and extinction causes. The ESR analysis was made on both crushed tooth enamel and sediment from the study area. They were subjected to Neutron Activation Analysis to determine the concentration of U, Th and K. The ESR dating indicated an age somewhere between 60,000 and 55,000 a for this N. platensis population (Lujanian, the last age of the Late Pleistocene South American Land Mammal Ages - SALMA). The date found for these gomphotheres is included in the Middle Pleniglacial, which is characterized by a cold and arid climate. Previous paleodiet studies suggest that the feeding habits of those individuals were basically opportunistic/generalist herbivores (C_3 grasses and woody plants). Taphonomically, it was observed that the gomphotheres carcasses were transported by a high-energy water stream, typical of fluvial systems, and that the large amount of individuals in the fossil record is due to a mass death event related to a dry period. Based on taphonomical, paleoecological and chronological evidence, it is possible to assume that the gomphothere population from the Quaternary of Aguas de Araxa is probably an example of individuals that suffered from climate changes during the Late Pleistocene in South America.