What era did the monkey evolve?

It's not accurate to say monkeys evolved in a single era. Here's why:

* Evolution is a gradual process: Monkeys didn't suddenly appear in a specific time period. Their evolution has been ongoing for millions of years.

* Different monkey lineages: There are many different types of monkeys, and they each have their own evolutionary history.

* Shared ancestry: Monkeys share a common ancestor with humans and other primates. This ancestor lived many millions of years ago.

Here's a simplified timeline:

* 55 million years ago: The earliest primates, the ancestors of monkeys, apes, and humans, appeared.

* 30 million years ago: The first true monkeys likely emerged, diverging into the New World monkeys (platyrrhines) and Old World monkeys (catarrhines).

* 25 million years ago: Old World monkeys further diversified into different groups, including baboons, macaques, and colobus monkeys.

* Present: Monkeys continue to evolve and adapt to their environments.

So, instead of talking about a specific era, it's more accurate to talk about the evolutionary history of different monkey lineages, which extends over many millions of years.