Redescribed and reinterpreted here is a partial skeleton of the oldest Antarctic penguin, Crossvallia unienwillia from the late Paleocene of Marambio (Seymour) Island. A thorough morphological analysis of limb bones (humerus, femur and tibiotarsus) allowed us to report both an amended reconstruction of type specimens and a revised taxonomic diagnosis of this large-sized early penguin. Moreover, an additional skeletal element, a single thoracic vertebra, is described for the first time. C. unienwillia is characterized by a mixture of features typical of both geologically older and younger penguins, supplemented by characters that are obviously unique. The above-mentioned findings shed new light on the very beginning of penguin evolution.

FAUNAL RECORD AND PALEOENVIRONMENTS OF THE LATE QUATERNARY, LA PAMPA PROVINCE, ARGENTINA. Fossil mammals from the Eastern sector of the Pampean Region (Argentina) provided the basis for the chronological and biostratigraphical continental scheme of the South American late Cenozoic. A new faunal assemblage from the Western area of the region (Santa Rosa, La Pampa Province) is presented along with the analysis of its sedimentary and stratigraphic context, and a paleoenvironmental reconstruction. The mammalian faunal assemblage is the largest and more diverse reported from a single locality in La Pampa province and is composed by Glyptodon clavipes Owen, Doedicurus sp. (Xenarthra, Cingulata), Megatherium americanum Cuvier, Glossotherium robustum (Owen), Scelidotherium sp. (Xenarthra, Folivora), Toxodon sp., (Notoungulata, Toxodontidae), Lama sp. (Artiodactyla, Camelidae), Equus (Amerhippus) sp. and Hippidion sp. (Perissodactyla, Equidae). The fossil bearing levels represent a fluvial-like channel environment that drained the rain water excess towards a nearby topographic depression (Laguna Don Tomás). According to the relative stratigraphic position in the sequence and the correlation with other localities of the region, the fossil bearing levels would have accumulated during the Late Pleistocene. Among taxa recovered at Sitio 1, Glyptodon clavipes, Megatherium americanum and Glossotherium robustum are characteristic species of the Bonaerian and Lujanian Stages-Ages, while Equus (Amerhippus) is an exclusive taxon of the Lujanian. Consequently, this new faunal assemblage is assignable to the Lujanian Stage-Age (Late Pleistocene-Early Holocene). Its presence in the analyzed deposits confirms the chronology proposed from the bearing levels.

TAPHONOMY OF THE THEROPOD DINOSAUR ANIKSOSAURUS DARWINI, BAJO BARREAL FORMATION, LATE CRETACEOUS OF PATAGONIA (ARGENTINA). Aniksosaurus darwini is a coelurosaurian theropod from the Bajo Barreal Formation (Upper Cretaceous), south of Chubut Province, Patagonia, Argentina. The fossils include postcranial remains of 5 individuals and they were preserved in a overbank mantle deposit associated to a low-sinuosity fluvial system. A detailed analysis on the biostratinomic, fossildiagenetic, and paleoenvironmental aspects of the site of occurrence of Aniksosaurus allows us to recognize two meteorization stages and their possible association with the origin of accumulation of the skeletons. Moreover, tooth marks in one of the femora are preliminarily assigned to a small crocodyliform. The taphonomic study adds new anatomic evidence related to soft tissues. The holotype, MDT-Pv 1/48, is represented by an articulated right hindlimb including, femur, tibia, metatarsals and phalanges. The subaerial weathering and abrasion of the femur due to transport strongly contrast with the preservation of the rest of the hindlimb bones, suggesting the presence of a protecting soft tissue resembling the podoteca seen in extant birds. The presence of this soft tissue in Aniksosaurus, could support the early occurrence of this feature in basal coelurosaurians.