One of the most intriguing paleobiogeographical phenomena involving the origins and gradual sundering of Gondwana concerns the close similarities and, in most cases, inferred sister-group relationships of a number of terrestrial and freshwater vertebrate taxa, e.g., dinosaurs, flying birds, mammals, etc., recovered from uppermost Cretaceous/ Paleogene deposits of West Antarctica, South America, and NewZealand/Australia. For some twenty five extensive and productive investigations in the field of vertebrate paleontology has been carried out in latest Cretaceous and Paleogene deposits in the James Ross Basin, northeast of the Antarctic Peninsula (AP), West Antarctica, on the exposed sequences on James Ross, Vega, Seymour (=Marambio) and Snow Hill islands respectively. The available geological, geophysical and marine faunistic evidence indicates that the peninsular (AP) part of West Antarctica and the western part of the tip of South America (Magallanic Region, southern Chile) were positioned very close in the latest Cretaceous and early Paleogene favoring the "Overlapping" model of South America-Antarctic Peninsula paleogeographic reconstruction. Late Cretaceous deposits from Vega, James Ross, Seymour and Snow Hill islands have produced a discrete number of dinosaur taxa and a number of advanced birds together with four mosasaur and three plesiosaur taxa, and a few shark and teleostean taxa.

This book summarizes major aspects of the evolution of South American metatherians, including their epistemologic, phylogenetic, biogeographic, faunal, tectonic, paleoclimatic, and metabolic contexts. A brief overview of the evolution of each major South American lineage ("Ameridelphia", Sparassodonta, Didelphimorphia, Paucituberculata, Microbiotheria, and Polydolopimorphia) is provided. It is argued that due to physiological constraints, metatherian evolution closely followed the conditions imposed by global temperatures. In general terms, during the Paleocene and the early Eocene multiple radiations of metatherian lineages occurred, with many adaptive types exploiting insectivorous, frugivorous, and omnivorous adaptive zones. In turn, a mixture of generalized and specialized types, the latter mainly exploiting carnivorous and granivorous-folivorous adaptive zones, characterized the second half of the Cenozoic. In both periods, climate was the critical driver of their radiation and turnovers.