Trends in Proboscidean Diversity in the African Cenozoic

The evolution of the Order Proboscidea has been proposed as a series of adaptive shifts in response to changing environments and evolutionary trends in skull and dentition that were linked to increasing dietary specialization. The assumption that climate and environmental change are the driving forces behind evolution is prevalent in studies of adaptation and diversification. However, there are other forces at work that may be equally responsible for evolutionary change, those involving biotic interaction and competition. In this paper, a summary of the African proboscidean record is presented as a means to examine overall trends in diversity and adaptation. Specimens from 175 localities in East, Central, and Southern Africa were entered into a locality database. Proboscideans from these localities comprise 11 families, 27 genera, and 53 species. First Appearance Datum (FAD) and Last Appearance Datum (LAD) for each species were plotted in 1-million-year intervals. Three periods of diversification were noted, the first in the Oligocene, the second in the early-middle Miocene, and the last in the Pliocene. Three ecomorphological categories based on dental functional morphology were identified in each of the three periods, suggesting that these are stable categories through time. As a result, it is proposed that biotic competition (resulting in resource partitioning) played a more prominent role in proboscidean evolutionary change and diversity than previously thought.