1. Introduction

During most of the Cenozoic, South America was an “island continent,” sporadically connected with other landmasses. This feature resulted in the development of a peculiar biota in which endemic South American taxa were mixed with immigrants from other continents. The mammalian taxonomic diversity of South America was mainly composed of two groups: Metatheria and Eutheria. In this scenario, the carnivorous adaptive zone in South America was represented principally by metatherians (Sparassodonta). However starting in the late Miocene, this guild began to be occupied by placental carnivores (Eutheria, Carnivora), which, by the start of the Pleistocene, had become the dominant terrestrial predators. The changes in the ecosystems during the late Neogene were related to sparassodont extinction and subsequent placental immigration, in the context of the Great American Biotic Interchange. This book summarizes paleontological information about the origin, systematics, phylogeny, paleoecology, and evolution of the Sparassodonta and Carnivora, the two mammalian carnivorous groups in South America, including hypotheses about the interaction between these clades.