PATTERNS OF MAMMALIAN COMMUNITY EVOLUTION IN SOUTH AMERICA AND AFRICA DURING THE LATE NEOGENE IN RELATION TO CLIMATIC AND ENVIRONMENTAL CHANGE

Patterns of mammalian evolution in relation to climatic and environmental change provide crucial evidence for the assessment of processes that drive macroevolutionary trends in the fossil record. Here we test the hypothesis that if global climate change plays a major role in influencing the evolution of terrestrial communities, then similar or parallel pattern of faunal change may be recorded in different parts of the world. We focus on the late Neogene, a time of major climatic and environmental variation registered in marine records. The main faunal variables under consideration are diversity, turnover, and relative taxonomic abundance. The South American data derive from the Pampean region of Argentina, with a well-known and rich record of mammalian evolution. The African data derive from the newly built Turkana Basin Paleontology Database, which includes records from several geological formations that span the late Miocene to Pleistocene of northern Kenya and southern Ethiopia. Our results indicate that late Neogene Turkana Basin mammalian diversity fluctuated in cycles of approximately 1 million years. There were several episodes of high faunal turnover, especially at around 3.5, 2.7, 2.3, and 1.9 million years ago (Ma). Mammals indicative open and seasonally arid environments show a significant increase in relative abundance at the close of the Neogene, shortly after 2 Ma. In South America, cursorial and grazing mammals dominated land mammal communities. As in Africa, South American mammals also show several episodes of high faunal turnover, with peaks around 3.2, 2.2 and 0.8 Ma. The 3.2 Ma peak is correlated with a diastrophic Andean phase; the peak at 2.2 Ma with a strong fall of temperature; and the 0.8 Ma peak with a change from wet and temperate climatic conditions to a brief span of dry and probably cold climatic conditions. Also, the 2.2 to 0.8 million-year span was characterized by the alternation of dry-cold and warm-wet climatic conditions. Although climate appears to be a critical factor in driving the evolution of mammalian communities in both continents, regional tectonics modulate the signal derived from the paleontological record.