Understanding proboscidean evolution: a formidable task.

A new approach to proboscidean evolution depicts taxa in three major radiations. This approach highlights general proboscidean evolutionary trends and origins more than the specific relationships among them. Data from more than 55 million years of evolution help to interpret how the integration of primitive and derived characters was essential to proboscidean success. Only two, or perhaps three, species remain of approximately 164 that lived in the past. Extinct forms were extremely cosmopolitan, occupying a variety of habitats, from deserts to mountain tops, on all continents except Australia and Antarctica. Challenges for future investigators include a better understanding of structure and function of infrasonic call production and perception, brain features, and reproductive biology in extinct proboscideans based on inferences from living forms.