13-million-year-old infant skull sheds light on ape ancestry

A Kenyan discovery of a remarkably complete fossil ape skull reveals what the common ancestor of all living great apes – including humans – may have looked like.

The fossil skull of Alesi, a 16-month-old infant of the ape species Nyanzapithecus alesi who died 13-million years ago
The fossil skull of Alesi, a 16-month-old infant of the ape species Nyanzapithecus alesi who died 13-million years ago. (Image: Christopher Kiarie, © Isaiah Nengo, via the Leakey Foundation)

Mary Alexander

Scientifically, human beings are part of a family – called the hominidae, or great apes – that includes chimpanzees, gorillas and orangutans. We are related by a common ancestor that lived millions of years ago. A new fossil found in Kenya shows what that ancestor might have looked like.

Research on the fossil, published in the journal Nature on 10 August, was done by an international team led by Dr Isaiah Nengo of Kenya’s Turkana Basin Institute.

Nicknamed Alesi by its discoverers, the fossil comes from a critical period in the African past. It was spotted by Kenyan fossil hunter John Ekusi in 13-million-year-old rock layers in the Napudet area, west of Lake Turkana in northern Kenya, in 2014.

Dr Isaiah Nengo with Alesi fossil
Fieldworkers Akai Ekes and John Ekusi watch Dr Isaiah Nengo lift the sandstone block containing the Alesi fossil after six hours of excavation. (Photo © Isaiah Nengo, via the Leakey Foundation)

“The Napudet locality offers us a rare glimpse of an African landscape 13-million years ago,” says Craig Feibel of the US’s Rutgers University.

“A nearby volcano buried the forest where the baby ape lived, preserving the fossil and countless trees. It also provided us with the critical volcanic minerals by which we were able to date the fossil.”

The fossil specimen is the skull of an infant that died at the age of about 16 months. The skull is roughly the size of a lemon.

Among the great apes, humanity’s closest relative is the chimpanzee. Our common ancestor with chimpanzees lived in Africa 6- to 7-million years ago, and many spectacular fossil finds have revealed how humans evolved since then.

But little is known about the common ancestors of all great apes, the evolutionary line from which humans, chimpanzees, gorillas and orangutans split more than 10-million years ago. The relevant fossils are scarce, made up of just a few teeth and partial jaw bones.

Until now, this lack of evidence has made it difficult to answer two important questions. Did the common ancestor of the great apes come from Africa? And what did our common ancestor look like?

A front view of the Alesi skull
A front view of the infant skull. (Image © Fred Spoor, via the Leakey Foundation)

The unerupted adult teeth inside the skull indicate that the specimen belonged to a new species, Nyanzapithecus alesi. The species name is taken from the Turkana word “ales”, meaning “ancestor”.

Nyanzapithecus alesi was part of a group of primates that existed in Africa for over 10 million years,” said Nengo. “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.”

Watch Dr Isaiah Nengo and his team of scientists working on the fossil:

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