When Kenyan palaeoanthropologist Isaiah Nengo received a grant from the Leakey Foundation to carry out field studies in northern Kenya’s Turkana basin, few scientists wanted to join him in the harsh, sweltering landscape.
Nevertheless, he and a small team of local researchers went to Napudet, where they discovered a 13-million-year-old skull of an infant ape. It was the most complete ancient ape skull ever to be found.
“You find lots of bits and pieces, but never anything so amazing or spectacular,” said Dr Nengo.
John Ekusi, one of the fossil finders from the Turkana Basin Institute (TBI), had wandered off to smoke a cigarette when he saw something in the ground that he thought was an elephant bone. Dr Nengo knew right away that it belonged to an ancient ape.
With dental picks and brushes, the team carefully dug out the fossil. The skull was about the size of a tennis ball, meaning it belonged to a juvenile animal, but more tests had to be done to identify the type of ape.
The find happened in September 2014, but the discovery was officially published in August in the science journal Nature.
Napudet, on the western side of Lake Turkana, is now a dry stony area. However, during the Miocene period between five and 23 million years ago, the Turkana basin was a tropical forest with several animals.
“The only reason why this specimen was so well preserved is that there was a huge volcanic eruption that blanketed the whole area,” said Dr Nengo, who obtained his PhD in Biological Anthropology from Harvard University.
He is currently a professor and associate director with Stony Brook University of New York state, which is affiliated to TBI.
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The thick layer of ash percolated into the skull and preserved it for millions of years. This area of Napudet has previously yielded fossilised tree trunks dating to the same period, so Dr Nengo suspected there were more ancient remains to be found.
Rock specimens taken from the site were measured in a laboratory at Rutgers University of New Jersey, US, and were dated to about 13 million years ago, giving the age of the fossil.
Further high intensity X-ray scanning carried out at the European Synchrotron Radiation Facility in Grenoble, France, revealed the brain cavity and teeth embedded inside the skull. From the teeth, they were able to gauge the exact age of the ape — 485 days.
At first, it was thought that the animal was similar to gibbons, small apes found in the forests of south-east Asia.
However, x-ray photos revealed the formation of sensory apparatus in the inner ear which, among other things, helps to maintain balance. This suggested a primate that moved carefully in the trees, unlike gibbons that swing freely.
The fossil was classified in the genus Nyanzapithecus, also an extinct Miocene period primate, specimens of which have been found in Kenya. But the teeth structure was different from typical Nyanzapithecus, so researchers concluded that this was a new species of the vanished ape.
Dr Nengo named it Nyanzapithecus alesi. Ales means ancestor in the local Turkana language. They cannot tell whether Alesi was male or female because the infant was too young for its sexuality to be discerned from its skull.
The structure of the ear canal of N. alesi suggests that it is in the direct line of the ancestry that is believed to have given rise to humans and present-day apes.
It is difficult to find good fossil evidence in Africa beyond seven million years old. “All you get are teeth and jaws in Africa. There are skulls in Spain from eight million to 11 million years ago,” says Nengo.
Some scientists believe that humans originated in Europe or Asia. At 13 million years old, N. alesi takes the theory of human evolution back to Africa.
“People have been looking for this kind of fossil for 300 years. It’s the first time that we’ve come up with a skull this complete.” The fossil is currently housed at the Nairobi National Museum.