An exceptionally well-preserved skull dug up in East Africa is thought to represent the last common ancestor of all living apes, from gibbons to humans. The remains are those of an infant animal that died 13 million years ago, and could shed light on the early emergence of the lineage that would eventually give rise to us.

The baby ape fossil, called Nyanzapithecus alesi, comes from a time that is critical in the timeline of ape evolution. Dating to 13 million years ago, the skull may have belonged to the last common ancestor of all apes, which includes all 23 surviving species grouped into gibbons, orangutans, gorillas, chimpanzees, and humans. It also confirms what many thought about the origin of apes.

The finding, published in Nature, is the most complete extinct ape skull ever known from the fossil record. Nicknamed Alesi by those who discovered it, the fossil has been preserved in such exquisite detail that 3D scans of the remains show not only the interior of the brain case, but even the unerupted adult teeth still within the jaw, which suggests that the animal was around one year and four months old when it died.

“Nyanzapithecus alesi was part of a group of primates that existed in Africa for over ten million years,” explains Isaiah Nengo of Stony Brook University in a statement. “What the discovery of Alesi shows is that this group was close to the origin of living apes and humans, and that this origin was African.”

The skull looks superficially quite a lot like that of a gibbon, with the short snout suggesting it might well have been a baby. “This gives the initial impression that it is an extinct gibbon,” says co-author Chris Gilbert. “However, our analyses show that this appearance is not exclusively found in gibbons, and evolved multiple times among extinct apes, monkeys, and their relatives.”

The detailed analyses of the skull, including scans that mapped the inside of the brain case, revealed that its lifestyle probably differed significantly from that of modern-day gibbons. The size and shape of the balance organ found within the inner ear suggests that this early relative would not have been as fast or agile as the gibbons that came later.

The skull finally proves that previous Nyanzapothecus teeth did indeed belong to apes, and firmly ties the origin of the group to this region of the African continent.