ABSTRACT
The ancient mammalian stock of South America is known from fossiliferous localities of different geological ages: Laguna Umayo for the latest Cretaceous; Rio Chico and Itaborai for the late Paleocene; Casamayor and Musters and maybe Chiococa, Tama and Gualanday for Eocene. This chapter considers the mammalian exchanges that may have occurred have occurred between the austral continents whose paleontological documentation is richest, that is to say, South America and Africa. The classical systematic arrangements led very naturally to a search for an African origin for the Caviomorpha and the Platyrrhina, since Africa was the place where the nearest forms morphologically, were found. In order to support hypothesis, workers have approached this problem in two ways: by searching in North America for possible ancestors of the Caviomorpha and the Platyrrhina; by trying to discover some anatomical criteria allowing a demonstration of the phylogenetic independence of both neotropical groups with respect to the Old World ones.
