Final answer:
The Oligocene epoch is significant for the emergence of the Parapithecoidea and Propliopithecoidea, indicating the early evolutionary stages of New World and Old World monkeys.
Step-by-step explanation:
The Oligocene epoch saw the emergence of two major groups in haplorhine evolution: the Parapithecoidea and the Propliopithecoidea. These primates are critical in understanding the early stages of New World and Old World monkeys. The Fayum site in Egypt, dating back to the Oligocene, provided fossil evidence which suggests that the Parapithecoidea may represent the earliest ancestors of New World monkeys based on their distinctive third premolar, while the Propliopithecoidea, which possesses a dental formula of 2.1.2.3 similar to catarrhine primates, may represent the earliest Old World monkeys.