ABSTRACT
The early history of placental mammals is still too poorly known for anyone to be able to state when the initial radiation of the Order Primates actually occurred. These earliest well known primates come from only a tiny fraction of the Holarctic region as it was then constituted. It is entirely possible that many more genera and species of Order Primates had differentiated by that time but remain undiscovered. It is equally possible to interpret the considerable variety of Eocene primates as having derived from two or more stocks that have separated from other primate lineages at the same time as the middle Paleocene radiation. It is now well demonstrated that both primates and rodents were deployed in the two southern continents of Africa and South America by the early Oligocene. Hominoids, ceboids, and cercopithecoids are more closely related to each other than any is to the prosimian primates.
