A two-million-year-old skull fragment comes from the earliest baboon ever found, a new study reports. The fossil was found in Malapa, a cave in South Africa and a Unesco World Heritage site where specimens of Australopithecus sediba, an early ancestor of modern humans, were discovered in 2010.

The ancient baboon, Papio angusticeps, is the first nonhominin primate found at the site.

The baboon bore a strong resemblance to its modern descendants, said Christopher C. Gilbert, an anthropologist at Hunter College in New York and an author of the study, published in PLOS One.

“You’d be hard pressed to figure out the difference between this fossil and a skull of a living baboon,” he said.

Little is known of the origins of modern baboons. Previous molecular studies suggested that baboons diverged from their closest ancestors about two million years ago, and the fossil skull seems to confirm that. The finding will help researchers to more accurately date fossil sites where remains of the ancient baboon are found, Dr. Gilbert said.