Evolutionary patterns of the mammals of the “Age of the Austral Plains” (Late Miocene–Early Pleistocene) from the southern cone of South America

Abstract

The “Age of the Austral Plains” fauna of South America evolved between the Middle Miocene and the Pleistocene, a time with important environmental changes and biogeographic events. Evolutionary and recent studies of this fauna are very limited. Our aim is to analyze an expanded database of Late Miocene–Early Pleistocene mammals of southern South America, using the fossil record but controlling for preservation and sampling biases, in order to assess the quality of the fossil record and study the evolutionary history of this fauna in terms of species longevity distribution, diversity, and evolutionary rates. Results indicate that the fossil record of the “Age of the Austral Plains” fauna is far from complete and more fieldwork and chronological constraints are needed. Longevities obtained are comparable with the calculated for other mammals on other continents, but the use of different approaches impacts the results. The distribution of the longevity in different diet or body size classes showed that generalists and intermediate body size classes have larger median values, but the pattern is weak and there is a wide overlap between groups. Age-dependent extinction (ADE) analysis found that the “Age of the Austral Plains” fauna has a negative pattern between longevity and extinction rate, but the explanation of this pattern is not clear, and the impact of singletons should be further evaluated. The diversification, turnover, and demise of this fauna were probably related to environmental changes (global climates, tectonics), but the role of North American immigrants in its decline should be further explored.