THE VALUE OF CINGULATA IN SOUTH AMERICAN PALEOGENE BIOSTRATIGRAPHY

A. A. CARLINI, M. R. CIANCIO, G. J. SCILLATO-YANÉ AND R. H. MADDEN

Rio de Janeiro, Brasil

Congreso; II Congreso Latinoamericano de Paleontología de Vertebrados; 2005

Heretofore, most biostratigraphic sequences have been proposed or substantiated on the basis of southern ungulate and/or marsupial evolutionary stage and diversity. Recent large samples of microfossils collected in Patagonia, Argentina, permit an evaluation of the value of cingulate assemblages for biostratigraphy. The Sarmiento Formation at Gran Barranca yields uniquely complete stratigraphic sampling of Cingulata, starting from Cifelli’s “Barrancan” at the base up to a Pansantacrucian level at the top of the composite section. Throughout this sequence, the composition of cingulate assemblages appears to respond with expectations based on temperature trends as estimated by the Southern Ocean δ18O record. On the Eocene, while the Dasypodinae Astegotheriini decrease in diversity (while temperatures decresing), the Dasypodinae Stegotheriini and Euphractinae appear and become dominant and diverse. Among “glyptodontoids”, different lineages are represented by very primitive patterns of surface sculpture, but these lineages become reduced dramatically after the Eocene-Oligocene Transition, giving rise to new lineages that were dominant during the rest of the Paleogene. The cingulate record indicates that between “Barrancan” and Mustersan levels there occurs a distinct and new faunal assemblage intermediate in composition that may represent a new Subage. Elsewhere in Patagonia, we recognize another new intermediate Paleogene assemblage in the basal part of Sarmiento Fm that is more primitive than Cifelli’s ‘Vacan’ but more advanced than the Riochican. During this interval of the Paleogene (Riochican-Vacan) marine temperatures increase as does diversity among Dasypodidae