Which primate is the closest relative to the common ancestor of all primates?

The last common ancestor between Homo sapiens and their closest relatives among other apes (Chimpanzees) occurred around 6 to 8 million years ago. Because this field is such a new one, and because the information is so limited, as of yet it is difficult to assign a specific species to the common ancestor. Right now the closest we have come is Sahelanthropus tchadensis.