Final answer:
The presence of Purgatorius in the Paleocene period reflects an early stage in primate evolution, potentially indicative of a common ancestor to modern primates due to shared dental features that have persisted over time.
Step-by-step explanation:
In the Paleocene period (66-56 million years ago), the presence of Plesiadapiformes, such as Purgatorius, signifies a pivotal stage in primate evolution and development. As the most primitive primate-like creatures, with characteristics like an elongated last lower molar and an enlarged upper central incisor, they are thought to possibly represent an early stage in the evolution of the common ancestor of later primates. These features are shared by all living primates today, suggesting a continuity in certain dental adaptations from this ancient time to our current era. By the end of the Paleocene, Purgatorius disappeared, and during the subsequent Eocene epoch, primates showing features closer to modern-day primates emerged. Evolution in primates progressed remarkably in the Eocene, with adaptations suited to arboreal life, such as the bone-enclosed postorbital bar, becoming evident. Comparatively, no fossil primates from the Eocene have been found in South America or Antarctica, but they are widespread in other regions.