Bay Area professor leads landmark discovery of baby ape skull

A routine day of digging for fossilized tooth fragments in northern Kenya was coming to an end for Isaiah Nengo when the Bay Area anthropologist stumbled onto the kind of find that defines a career — a breakthrough discovery that could help solve the enduring mystery of where humans come from.

On a rocky outcropping beneath a hot summer sun, the De Anza College professor and his research team unearthed the skull of what they say was a baby ape that lived in the forests of East Africa some 13 million years ago.

The spectacularly preserved skull, described in a landmark report to be published Thursday in the journal Nature, was about the size of a lemon and in better shape than any specimen of its kind. Moreover, it offered a rare look at what is believed to be a shared ancestor of today’s apes and humans.

The cranium is that of a young primate that had ears, a nose and a jaw with human similarities but more closely resembled a monkey or gibbon.

The skull of a 13-million year old baby ape, dubbed Alesi, is partially excavated after careful removal of loose sand and rocks with dental picks and brushes in northern Kenya. The skull of a 13-million year old baby ape, dubbed Alesi, is partially excavated after careful removal of loose sand and rocks with dental picks and brushes in northern Kenya. Photo: Isaiah Nengo / Isaiah Nengo Photo: Isaiah Nengo / Isaiah Nengo Image 1 of / 12 Caption Close Bay Area professor leads landmark discovery of baby ape skull 1 / 12 Back to Gallery

“We were walking back to our field vehicle to drive back to our camp,” Nengo, a 55-year-old Marin County resident, recounted in an email to The Chronicle as he flew home from Kenya on Wednesday. “One of the field assistants started to roll a tobacco cigarette and we chased him away. As he walked ahead of us, we saw him milling around this one spot and realized he had found something.

“We got there,” he said, “and brushed away the sediment to reveal the dome of the skull (and) we instantly recognized it was the skull of a primate.”

The discovery helps piece together the evolutionary puzzle of how and where the human lineage emerged before it split with gorillas, orangutans and chimpanzees. While scientists have learned a great deal about recent human evolution through such famed fossil finds as Lucy, the 3.2 million-year-old human-like skeleton, and younger Neanderthals, the distant past remains a big unknown.

Unlike previous clues into this murky period, which are limited to small fragments of jaws and teeth, Nengo’s discovery, dubbed Alesi, introduces an entire skull to the fossil record.

“It’s hard to imagine how something like that could be preserved and not just fall apart,” said John Fleagle, an anthropologist at Stony Brook University in New York who worked with Nengo and co-authored this week’s publication. “This gives us a huge insight into a group of fossil apes that was only known from bits and pieces.”

Nengo and his team excavated the skull from ash that had spewed long ago from a volcano in the dry Napudet Hills, west of Kenya’s Lake Turkana. The eruption helped preserve the cranium, which, like other relics of the era, might have withered in what was then lush jungle.

While the area has been a hotbed of fossils, most of the region had been picked through before Nengo arrived five years ago. Nengo said he was looking primarily for ape teeth when the fully intact skull emerged.

With help from the European Synchronton Radiation Facility in Grenoble, France, which took powerful X-ray scans of the skull, Alesi was found to be a year and four months old when he or she died. The ape’s gender is not known, nor is the cause of death.

While similar in appearance to a baby gibbon, the ape had features that signaled an indisputable link to more modern apes and humans, such as bony ear tubes, a wide nasal passage and teeth in certain positions, as well as a larger brain cavity than other primates of the period, the researchers said.

The skull continues to be studied, but already the distant human ancestor has been deemed a new species of ancient ape, named Nyanzapithecus alesi.

“We get a much clearer look at what came before humans arrived on the scene,” Nengo said.

Scientists believe the human lineage made the extraordinary leap from that of other apes about 6 or 7 million years ago, sharing its last kinship with a type of chimpanzee.

The common relative of apes and humans, which are known collectively as hominoids, gave rise to many of today’s human traits. The shared ancestors lived in complex social groups in forests, but what they looked like, where exactly they lived and how they evolved are continuing subjects of inquiry.

Nengo, who was born in Kenya and lives in Ross, has spent the past five summers in northern Kenya trying to answer these and other evolutionary questions. He’s currently on leave from De Anza in Cupertino, where he has taught for 14 years, and works as a research professor at Kenya’s Turkana Basin Institute. But his team includes several students from the South Bay community college.

Nengo’s work was supported by the Leakey Foundation, the Foothill-De Anza Foundation, the Fulbright Scholars Program, the National Geographic Society, the European Synchrotron Radiation Facility and the Max Planck Society.

“A lot of times we don’t pay a lot of attention to our older ancestors, but to be able to go back 13 million years, it’s quite exciting,” said Sharal Camisa, executive director of the Leakey Foundation in San Francisco, which funds research into human origins. “It’s remarkable to think that this is part of our story.”