Final answer:
The Paleocene epoch is when the earliest known primate ancestor, Purgatorius, appeared, indicating the beginning of primate evolution.
Step-by-step explanation:
The Paleocene epoch had the appearance of the primate ancestor. The Paleocene began approximately 65 million years ago (MYA) and ended around 54 MYA. It's considered significant for primate evolution as it contains the first unequivocal record of the earliest primates. A notable discovery is of Purgatorius, the most primitive primate yet identified, found in a geological deposit dated to the earliest part of the Paleocene in Montana. Characteristics such as an elongated last lower molar and an enlarged upper central incisor, both traits found in current primates, suggest that Purgatorius may be the common ancestor of later primates.