What are the monkeys called with big heads?

There isn't a specific type of monkey called "big head monkeys". Monkeys are a diverse group with many different sizes and shapes.

However, some monkeys known for their large heads or faces include:

* Mandrills: These are among the largest monkeys and are easily recognizable by their vibrant colors and large, prominent muzzles.

* Proboscis Monkeys: These monkeys have very long noses that hang down, giving them a distinctive, "big head" appearance.

* Hamadryas Baboons: These baboons have large, dog-like heads with prominent muzzles and thick manes of hair.

If you can give me more information about the specific monkey you are thinking of (like where you saw it or what other characteristics it had), I might be able to give you a more specific answer!