Together, the new finds and the puzzling skull describe a species of early humans clearly distinct from two others known from fossils from the same period, said Meave Leakey, the 70-year-old paleoanthropologist who led the team that discovered the fossils.
The “base of the human lineage was indeed diverse,” Leakey said from her longtime home at the Turkana Basin Institute in northern Kenya. Her colleagues made the finds near there.
Long thought to be the seat of human origins, East Africa was once “quite a crowded place with multiple species,” said Fred Spoor of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, a co-author of a report describing the finds.
Leakey and her colleagues stop short of assigning the fossils a species name. But 20 years ago, others scientists classified the 40-year-old mystery skull as Homo rudolfensis.
An associate of Leakey’s noticed a jawbone sticking out of a block of sandstone in the arid region in 2007. After hauling the block to their laboratory, the team whittled away with dental drills and revealed a face, its right cheek and upper jaw intact. The small fossil likely came from an adolescent, Leakey’s team reports in this week’s issue of the journal Nature.
Nearby, the team also found two partial jawbones that match both the new skull and the mystery skull, Spoor said. All of the fossils date between 1.78 and 1.95 million years old.
At that time, East Africa was a roiling hotbed of human evolution. Other fossil finds show that the long-lived species thought to be the direct ancestor of modern humans, Homo erectus, thrived in the region, which was undergoing rapid changes in plant cover, rainfall and, in all likelihood, availability of various foods.
Meanwhile, another group of early human fossils from the region has been classified as Homo habilis, which means “handy man,” as these creatures were thought to create primitive stone blades.
Yet another, more primitive hominid species, called Paranthropus bosei, also lived in the region at the time. Stout-bodied and with giant molars, these beings more closely resembled the more ape-like creatures known as the Australopitecines and are not thought to be human ancestors. Instead of evolving, they died out.
But the new finds — and the mystery skull — clearly don’t belong to any of these groups, said Leakey, who is also a National Geographic explorer-in-residence. The face is too flat, falling like a cliff from brow to chin. The front teeth line up straight as a ruler instead of arcing forward as in the other human species. The molars are also quite large, and, as the mystery skull shows, the brain was bigger — though still only roughly half the size of that of a modern human.