Early primate evolution in Afro-Arabia.

The peculiar mammalian fauna that inhabited Afro-Arabia during the Paleogene first came to the attention of the scientific community in the early part of the twentieth century, when Andrews1 and Schlosser2 published their landmark descriptions of fossil mammals from the Fayum Depression in northern Egypt. Their studies revealed a highly endemic assemblage of land mammals that included the first known Paleogene records of hyraxes, proboscideans, and anthropoid primates, but which lacked ancestors of many iconic mammalian lineages that are found in Africa today, such as rhinos, zebras, bovids, giraffes, and cats. Over the course of the last century, the Afro-Arabian Paleogene has yielded fossil remains of several other endemic mammalian lineages,3 as well as a diversity of prosimian primates,4 but we are only just beginning to understand how the continent's faunal composition came to be, through ancient processes such as the movement of tectonic plates, changes in climate and sea level, and early phylogenetic splits among the major groups of placental mammals. These processes, in turn, made possible chance dispersal events that were critical in determining the competitive landscape--and, indeed, the survival--of our earliest anthropoid ancestors. Newly discovered fossils indicate that the persistence and later diversification of Anthropoidea was not an inevitable result of the clade's competitive isolation or adaptive superiority, as has often been assumed, but rather was as much due to the combined influences of serendipitous geographic conditions, global cooling, and competition with a group of distantly related extinct strepsirrhines with anthropoid-like adaptations known as adapiforms. Many of the important details of this story would not be known, and could never have been predicted, without the fossil evidence that has recently been unearthed by field paleontologists.