The Fossil Mammal Fauna of South America

Of the three southern continents, South America was more isolated during the Tertiary than Africa, less isolated than Australia. Its record of Cenozoic mammalian life is better than that of either. This record suggests that around the beginning of the Cenozoic, South America received a few wait immigrants-marsupials, edentates, ungulates-that reached the continent across a water barrier. The source area was probably Central America, which formed a tropical North American peninsula until near the end of Tertiary time. A few later wait immigrants reached the continent across the water barrier-rodents in the later part of the Eocene, primates then or in the early Oligocene, and procyonids perhaps late in the Miocene. From the descendants of these few immigrants a balanced fauna evolved that was strikingly different in composition from those of other continents. The evolution of the various groups composing it is briefly presented and discussed. At the end of the Tertiary the isolation of the continent ended with the establishment of the Isthmus of Panama. Faunal interchange between North and South America then began and is still going on. Most of the northern participants in the interchange penetrated deeply into South America. The southern participants, advancing into a continent subjected to periodic continental glaciations, were less successful, the majority of them not penetrating beyond the tropical area. Competition and extinction during the faunal interchange went on mainly among the carnivores, the southern marsupials being replaced by the northern placentals. The spectacular extinctions, involving mainly large mammals of both northern and southern ancestry, came at the end of the Pleistocene; the arrival of man was probably a major factor.