The 13-million-year old Babe Ape
The dry, stony terrain of Turkana basin in northern Kenya has yielded a treasure trove of prehistoric animal, plant and human remains for many decades. Now the discovery of the fossilised skull of a baby ape has brought new insight to primate evolution and the ancestry of human beings.
Kenyan palaeoanthropologist Dr Isaiah Nengo, who led the excavation says, “People have been looking for this kind of fossil for 300 years. You find lots of bits and pieces, but never anything so amazing.” The find happened in September 2014 and was officially published in August 2017 in the scientific journal, Nature.
Dr Nengo grew up in Kenya, and is a professor and associate director with Stony Brook University of New York state which is affiliated to the Turkana Basin Institute (TBI) of Kenya. Two years ago, Nengo obtained a study grant from the Leakey Foundation for field studies but few scientists wanted to join him in the uncomfortably hot Turkana Basin. So Nengo gathered a small team of Kenyan researchers and headed north.
During this expedition in the Napudet area of Turkana, fossil finder John Ekusi of TBI was taking a cigarette break when he spotted something interesting in the ground. Ekusi thought it was part of an elephant knee. Dr Nengo immediately recognised it as part of an ape skull.
It took a whole day to excavate the fossil which turned out to be almost intact, the most complete prehistoric primate skull ever to be found. The fossil was small, about the size of a tennis ball but further tests had to be done to identify it properly.
Primates fossils are particularly difficult to find because they live in tropical forests, typically humid habitats where dead bodies decompose quickly. But between 5-23 million years ago, during the Miocene era, the Turkana ecosystem had thick vegetation, many trees and a wider variety of animals.
Today, there are no chimpanzees or other primates living wild in Kenya, and the Napudet area has no trees. This fossil skull has survived because of a huge volcanic eruption that buried the region under tens of meters of ash. “Volcanic ash has a material called calcium carbonate which is like cement. It percolates into the bone and preserves it really well. One of those accidents of nature,” explained Dr Nengo, who has a PhD in Biological Anthropology from Harvard University.
Initially the fossil was thought to be related to gibbons, apes living in the rainforests of south-east Asia where they swing nimbly in tree canopies. X-ray scanning of the skull at the European Synchrotron Radiation Facility in Grenoble, France showed the formation of apparatus in the inner ear which, among other things, is used like a gyroscope for maintaining balance. This suggests a primate that moved carefully in the trees. Earlier excavation in Napudet have revealed 98 fossilised tree trunks that formed part of an ancient forest.
X-rays of the specimen showed the brain cavity and adult teeth embedded in the little skull. From the teeth, scientists were able to figure the exact age of the ape – 485 days old, or 1 year and 4 months. They cannot tell whether it was male or female because the infant was too young for gender to be determined just from the skull.
At a laboratory in Rutgers University of New Jersey, USA samples of rock from the site were studied and dated to 13 million years ago, giving us the time period of the fossil.
The fossil was classified in the genus Nyanzapithecus, a Miocene era ape. Others this genus have been found in Kenya but differences in the teeth structure pointed to a new species of extinct ape. Dr Nengo, who specialises in the study of the Miocene period, named the fossil Nyanzapithecus alesi. Ales means ‘ancestor’ in the local Turkana language. He says, “This new species is part of a larger group which is most likely the ancestor of humans and apes.”
Apes are the closest relatives of human beings. We share more than 98% of our genetic material of chimpanzees and bonobos pointing to a common ancestor. The discovery of Alesi has brought back a controversial debate about human evolution in Africa, with one school of scientiests insisting that evolution took place in Europe or Asia, not in Africa. Dr Nengo views it as the subtle belief that nothing as good as the human or the human lineage can come out of Africa.
He says, “We want to know where and when did the common ancestor exist? We’ve not had very good evidence up until this point, conclusive evidence to show that it is for sure Africa,” explains Dr Nengo.
Human beings with their regional anatomical differences have lived on earth for only about 40,000 years. The skeleton of the hominin called ‘Lucy’ (Australopithecus afarensis) that discovered in Ethiopia in 1974 is 3.5 million years old. The skull of the hominid (Sahelanthropus tchadensis) found in Chad is 6 million years. In Europe, skulls of prehistoric human ancestors found in Spain date between 8-11 million years. “If we push past 7 million years in Africa it becomes dicey, all you get are teeth and jaws.
With this new skull from Kenya at 13 million years, the story of human ancestry has returned to Africa. Says Nengo, “Africa is the origin not only of the ancestor that we share with the chimpanzees but the ancestor of all the apes. The very beginning of that family happened in Africa.”