Final answer:
During the earliest part of primate evolution, several significant changes occurred globally. The first true primates appeared around 55 million years ago in the Eocene epoch. Over time, these early primates underwent evolutionary changes and eventually gave rise to monkeys.
Step-by-step explanation:
During the earliest part of primate evolution, several significant changes occurred globally. The first true primates appeared around 55 million years ago in the Eocene epoch. These early primates resembled present-day prosimians like lemurs, but over time, they underwent evolutionary changes such as larger brains and eyes, and smaller muzzles. By the end of the Eocene epoch, many of these early prosimian species went extinct due to cooler temperatures or competition from the first monkeys.
In the Oligocene epoch, which started around 34 million years ago, the first fossil monkeys appeared. The earliest haplorrhine fossils were found in Egypt and are believed to be the earliest New World and Old World monkeys. These primates had dental formulas that indicated the number and type of teeth they had. The Oligocene epoch marked an important stage in primate evolution.
The Paleocene epoch, which began around 65 million years ago, is also significant in primate evolution because it offers the first unequivocal record of the earliest primates. The most primitive primate identified so far is Purgatorius, which was found in Montana, USA. Purgatorius shares characteristics with extinct and living primates, suggesting that it may be the common ancestor of later primates. These discoveries provide valuable insights into the early stages of primate evolution globally.