EOCENE MAMMALS AND CONTINENTAL STRATA FROM PATAGONIA AND ANTARCTIC PENINSULA JAVIER N. GELFO 1 , MARCELO A. REGUERO 1 , GUILLERMO M. LÓPEZ 1 , ALFREDO A. CARLINI 1 , MARTÍN R. CIANCIO 1 , LAURA CHORNOGUBSKY 2 , MARIANO BOND 1 , FRANCISCO J. GOIN 1 , AND MARCELO TEJEDOR 3 1 División Paleontología Vertebrados, Museo de La Plata, Paseo del Bosque s/n, B1900FWA La Plata, Argentina, jgelfo@fcnym.unlp.edu.ar 2 Sección Paleontología de Vertebrados. Museo Argentino de Ciencias Naturales Bernardino Rivadavia. Av. Angel Gallardo 470 (C1405DJR) Buenos Aires, Argentina 3 LIEB (Laboratorio de Investigaciones en Evolución y Biodiversidad), Facultad de Ciencias Naturales, Sede Esquel, Universidad Nacional de la Patagonia “San Juan Bosco,” Sarmiento 849, 9200 Esquel, Provincia del Chubut, Argentina ABSTRACT—The mammalian faunal succession in South America is well documented throughout the Eocene from about 47 to 37 Ma. Most Eocene land mammal-bearing deposits occur in Patagonia and in basins of the Antarctic Peninsula, and these have been studied intensely over the last 20 years. The geology of the San Jorge (eastern Patagonia), “Volcanic-Pyroclastic Complex” (western Patagonia), and James Ross (Antarctic Peninsula) basins are here reviewed and their faunal content analyzed. The geochronology of Itaboraian and Riochican South American Land Mammals Ages (SALMAs), usually regarded as late Paleocene, is also discussed. In order to evaluate the similarity between Eocene faunas, a cluster analysis applying the Simpson coefficient was performed using a data matrix with 13 faunas and 228 taxa. The faunas represent both classic and new localities from Antarctica, Patagonia, Mendoza, and central Chile, and we analyzed three taxonomic categories (genus, family, and order) so that faunas lacking common genera could be compared. The analysis supports at least three major clusters. The first, which consists of faunas from western Patagonia (the Paso del Sapo localities) plus Antarctica, seems to fall biochronologically between the Riochican and Casamayoran SALMAs. The second cluster is divided between faunas related to the Casamayoran and those related to the younger Mustersan SALMA. The latest Eocene-earliest Oligocene faunas also group together and are represented by three Tinguirirican faunas plus a fourth younger fauna which seems to be pre-Deseadan (Oligocene). INTRODUCTION In the last two decades, the Paleogene deposits of Patagonia and the Antarctic Peninsula have been the focus of concentrated paleontological and geological fieldwork. Our knowledge of Paleogene mammalian faunas in these two regions has increased markedly since the 1980s. As an example, the biochronological sequence for the South American Paleogene underwent no relevant changes from 1948 through the middle 1980s (Simpson, 1948; Marshall et al., 1983; Pascual et al., 1965, Patterson and Pascual, 1972). Major progress and results have been achieved for the continental Eocene in these two areas of the Southern Hemisphere. Thus, the overview presented here focuses primarily on the taxonomy, biostratigraphy, biogeography, and geochronology of Eocene continental mammals, all of which have been substantially improved in recent years (e.g., Kay et al., 1999, 2001; Gelfo et al., 2009). For many years, significant Eocene mammal faunas were known primarily from Argentina, a situation that largely prevails today. In the original proposal of a biochronological subdivision for the Cenozoic of South America (Pascual et al., 1965), three South American Land Mammal Ages were defined for the Eocene. These were based on Ameghino’s (1906) and Simpson’s (1948) faunas, namely the Casamayoran, Mustersan, and Divisaderan, which were considered lower, middle, and upper Eocene, respectively (Pascual et al., 1965). Since then the original proposal has undergone many important changes, and subsequent taxonomic, geochronological, and biostratigraphic studies have greatly contributed to an improved understanding of the evolution and succession of the South American Cenozoic mammalian assemblages (Flynn and Swisher, 1995, and references therein; Pascual et al., 1996). Gelfo et al. Eocene mammals from Patagonia and Antarctica Museum of Northern Arizona Bulletin 65, Flagstaff, Arizona. Papers on Geology, Vertebrate Paleontology, and Biostratigraphy in Honor of Michael O. Woodburne.