The skull of a 29 million-year-old monkey has been found in Saudi Arabia.
Researchers are hoping that it could provide vital clues on how apes and humans evolved millions and millions of years ago.
The monkey, called Saadanius hijazensis, had things in common with monkeys and apes, and humans, today.
It would have looked a bit like a capuchin monkey, and would have used all four of its limbs to run around in the trees.
Scientists think it probably laid down in the trees when it wanted to rest, rather than sitting on the floor like most modern monkeys.
One of the scientists said the ancient skull was an "extraordinary find".