By Kari Mutu

The recent find of a fossilised skull of a 13-million-year-old primate has brought new understanding about the evolution of early humans. The skull belongs to an infant ape that lived in northern Kenya’s Turkana Basin.

The discovery happened the Napudet area of Turkana County during field excavations in led by Kenyan palaeontologist Isaiah Nengo. One late afternoon, a fossil finder in his team called John Ekusi was taking a cigarette break when he noticed something peeping out of the ground. Ekusi thought it was part of an elephant femur. Nengo, who specialises in primate and human evolution, immediately recognised it as the cranium of an ape.

The following day, and after several hours of careful digging, they extracted an almost intact specimen.  “People have been looking for this kind of fossil for 300 years and it’s the first time that we’ve come up with a skull this complete,” said Nengo, who is an associate director and research assistant professor at State University of New York at Stony Brook, United States.

Kenya is a renowned fossil hunting ground, but the pre-historic animals that have eluded scientist for many years are primates. Apes live in forests which are typically humid habitats where dead matter decomposes fairly quickly. This particular fossil, which is smaller than a tennis ball, survived because of a huge volcanic eruption that blanketed the area in ash. “Volcanic ash has calcium carbonate which is like cement. It percolates into the bone and preserves it really well. One of those accidents of nature,” said Nengo.

The semi-desert Napudet region west of Lake Turkana was once a tropical forest where scientists have found ancient tree stumps still standing as they were buried 13 million years ago. So Nengo knew the site had promise for other finds. But even after getting a grant from the Leaky Foundation, he had difficulty convincing other researchers to join him in the hot and hostile terrain. Undaunted, he gathered a crew of local fossil finders and travelled north. Working out of the Turkana Basin Institute (TBI), a research station that is supported by Stony Brook, they spent two weeks in the field before making the incredible discovery.

Nengo cut his teeth as a volunteer at the Nairobi National Museum under the tutelage of palaeoanthropologists Richard and Meave Leakey, before moving to the United States where he has lived and worked since the early 1990s. Now he has come back full circle to TBI which was founded by the Leakeys.

Further investigations were needed to determine the type of primate. After receiving permission from the Kenya government, Nengo took the specimen for intense X-ray scanning at the European Synchrotron Radiation Facility in Grenoble, France. The scans revealed the inner features of the brain cavity and that adult teeth were all in place. This enabled scientists put the age of the ape at 485 days, or 16 months. The infant is too young for the gender to be determined from the head alone.

At a laboratory at Rutgers University in New Jersey, USA, rock specimens were measured and dated to about 13 million years ago, which is in the Miocene period that ranges from 5 million to 25 million years ago.

From the shape of the snout, the ape was first thought to be related to gibbons that live in Asian forests. But the formation of sensory apparatus in its inner ear which, among other things, helps to maintain balance suggested a primate that moved carefully in the trees, unlike gibbons that move very nimbly.

The ape is also a new species and Nengo named it Nyanzapithecus alesi. The word ales means ‘ancestor’ in the Turkana language.

As a Miocene-period primate, Alesi fills in critical gaps in the human evolution story. The anatomy of the ear canal indicates a primate in the direct line of ancestry of humans and present-day apes. Palaeoanthropologists have long differed on whether the common ancestor of humans and apes evolved in Africa or Europe and Asia.  Nengo describes it as a subtle attempt at superiority in western science. “The notion that nothing as good as the human lineage can come out of Africa.”

Until now there was insufficient proof to support the Africa origins story. Fossil records from Turkana basin of the hominin Homo erectus go back 2 million years. The skeleton Australopithecus afarensis, commonly known as Lucy found in Ethiopia, is 3.5 million years old. The skull of Sahelanthropus tchadensis discovered in Chad is around 6 million years old. “If we push past 7 million years you don’t get much in Africa,” says Nengo who has a doctorate degree in Biological Anthropology from Harvard University.

But in Europe, fossil skulls have been found in Spain that date between 8 and 11 million years. Now at 13 million years, Nengo is certain Alesi provides the evidence that the common ancestor of humans and apes evolved in Africa.

The findings were officially published in science journal, Nature, in August 2017 and the fossil is housed at the Nairobi National Museum.