Cione et al: Late Cenozoic extinction Rev.in South Mus. America Argentino Cienc. Nat., n.s.1 5(1): 000, 2003 Buenos Aires. ISSN 1514-5158 The Broken Zig-Zag: Late Cenozoic large mammal and tortoise extinction in South America Alberto L. CIONE1, Eduardo P. TONNI1, 2 & Leopoldo SOIBELZON1 1Departamento Científico Paleontología de Vertebrados, 'acultad de Ciencias Naturales y Museo, Paseo del Bosque, 1900 La Plata, Argentina. 2Laboratorio de Tritio y Radiocarbono, LATYR. 'acultad de Ciencias Naturales y Museo, Paseo del Bosque, 1900 La Plata, Argentina. E-mail:
[email protected],
[email protected],
[email protected]. Corresponding author: Alberto L. CIONE Abstract: During the latest Pleistocene-earliest Holocene, South American terrestrial vertebrate faunas suffered one of the largest (and probably the youngest) extinction in the world for this lapse. Megamammals, most of the large mammals and a giant terrestrial tortoise became extinct in the continent, and several complete ecological guilds and their predators disappeared. This mammal extinction had been attributed mainly to overkill, climatic change or a combination of both. We agree with the idea that human overhunting was the main cause of the extinction in South America. However, according to our interpretation, the slaughtering of mammals was accom- plished in a particular climatic, ecological and biogeographical frame. During most of the middle and late Pleis- tocene, dry and cold climate and open areas predominated in South America. Nearly all of those megamammals and large mammals that became extinct were adapted to this kind of environments. The periodic, though rela- tively short, interglacial increases in temperature and humidity may have provoked the dramatic shrinking of open areas and extreme reduction of the biomass (albeit not in diversity) of mammals adapted to open habitats.