Final answer:
The earliest platyrrhines in South America are not observed in the Eocene epoch, and their exact arrival epoch is unspecified, but they have origins dating back to the Oligocene epoch in Africa.
Step-by-step explanation:
The earliest platyrrhines, or New World monkeys, are not observed in the geological record of South America until after the Eocene epoch. The presence of a third premolar, a trait found in all New World monkeys, suggests that they have distant origins in the Fayum primates of the Oligocene epoch (approximately 34 MYA to about 22 MYA). Since there are no known fossil primates from the Eocene in South America, and given that the long geographical isolation of South America ended roughly 3 million years ago, which is well after the Oligocene, it can be inferred that platyrrhines arrived in South America sometime after the Eocene. However, the exact epoch in which they first appear in South America is not provided in the referenced materials. Therefore, while the beginnings of the group originate in the Oligocene in Africa, the epoch of their earliest appearance in South America remains unspecified with the given information.