After diverging from old world monkeys' ancestors between 25 and 28 million years ago, apes diversified near the middle of the Miocene epoch.
The lemon-sized skull was discovered in Kenya by an worldwide team of researchers, and was dated to the middle of the Miocene era, a little-understood time when many species of ape arose in Africa, including common ancestors of both modern apes and humans. This could be the biggest impact on ape evaluation.
Comparisons with other African ape fossils indicate that the infant's skull belongs to a new species that the researchers named Nyanzapithecus alesi.
Paleontologists have found bits of teeth and jaws from apes that lived during the Miocene, but traces of their skulls and limbs are exceptionally rare.
Furthermore, based on a 15-million-year-old arm fossil from a related species, researchers think Alesi probably didn't have long limbs that would have allowed it to swing through trees like gibbons.
What the team later excavated would end up being what is thought to be the most complete skull of an extinct ape species in the fossil record.
"The quality of our images was so good that we could establish from the teeth that the infant was about 1 year and 4 months old when it died", Paul Tafforeau, a researcher with the European Synchrotron Radiation Facility, said in a press release.
Researchers detailed their discovery this week in the journal Nature.
However, thanks to Alesi, scientists now know that N. Alesi had been part of a group of primates that roamed Earth more than 10 million years ago.
"More fossil prospecting at the Napudet site is well worth it since the chances of finding really exciting stuff there are very high", he added.
"There was some discussion for a while about whether the modern apes actually originated in Africa or in Eurasia, because gibbons today live in Southeast Asia, and this pretty squarely confirms that the origin of apes was in Africa".
The dating of the skull was done by analyzing the rock layer from which the fossil was pulled, and by measuring the argon isotopes.
A year after the discovery, Nengo obtained government clearance to carry the fossil from Kenya to the European Synchrotron Radiation Facility (ESRF) in Grenoble, France, to perform more tests on Alesi.
Its unerupted teeth placed the skull in the genus Nyanzapithecus as the first member of a brand-new species: Nyanzapithecus alesi. The researchers established this age by counting the layers within the fossilized dental structures, a process akin to counting tree rings.
A group of scientists have found what may be the most intact fossilized primate skull ever discovered, and the find could shed light on the common evolutionary heritage shared by apes and humans. "This complete skull - it is now forever going to be a touchstone for all future studies in primate evolution and growth and development in the apes, so it's fantastic in that way". If the animal was fully grown it would have weighed in at 25 pounds and looked like a gibbon.
The small snout of the skull would have made Alesi look like a baby gibbon. This evidence strongly suggests that Alesi was a true ape that lived after the split from monkeys.
We can't definitively say that modern apes and humans evolved directly from this newly discovered species - many more specimens from different eras would be needed to create that clear a picture. "That was important to know". Ellen Miller, an anthropology professor at Wake Forest University, contributed to the study. Scientists have found a 13-million-year-old ape skull that is amazingly well preserved, so much so that scientists can examine unerupted teeth and the impression left by the brain the skull once housed.
Since so little is known about the common ancestors of living apes and humans, Alesi can help reveal what they may have looked like.