Final answer:
Purgatorius was an early primate that lived during the Paleocene epoch, as evidenced by geological deposits dated around 63 million years ago.
Step-by-step explanation:
Purgatorius was an early primate in Montana that lived during the Paleocene epoch. This period began approximately 65 million years ago (MYA) and ended about 54 MYA. Purgatorius is known to have existed in geological deposits that are dated to the earliest part of the Paleocene, around 63 million years ago, suggesting that this creature could be the common ancestor of later primates, due to key dental features shared with living primate species. Characteristics such as an elongated last lower molar and an enlarged upper central incisor are indicative of its primitive primate lineage.