Final answer:
The first modern primates appeared approximately 55 million years ago during the Eocene epoch. They resembled present-day prosimians like lemurs and evolved to have larger brains and eyes, and smaller muzzles.
Step-by-step explanation:
The first modern primates appeared during the Eocene epoch, which occurred approximately 55 million years ago (MYA). These early primates were found in North America, Europe, Asia, and Africa and resembled present-day prosimians like lemurs. Over time, they evolved to have larger brains and eyes, and smaller muzzles. By the end of the Eocene epoch, many of the early prosimian species went extinct due to cooler temperatures or competition from the first monkeys. The order Primates is divided into two groups: prosimians and anthropoids.
Prosimians include bush babies, lemurs, and tarsiers, while anthropoids include monkeys and apes. Prosimians tend to be nocturnal, smaller in size, and have relatively smaller brains compared to anthropoids. The first fossil monkeys appeared during the Oligocene epoch, which started around 34 MYA. The earliest haplorrhine fossils were found at the Fayum in Egypt and are believed to be the earliest New World and Old World monkeys. These monkeys can be identified based on their dental formula, which indicates the number of each type of teeth they have.