The face and cranium of the fossil have characteristics similar to those of an early-human species, such as Homo erectus. But there is anatomical evidence that the fossil is part of modern humans' ancestry. Simpson says, for example, that the shape of the skull's dome, or vault, is similar to that of modern humans.
"If you look at Homo erectus, their vaults tend to be low, long, and angular," Simpson said. "This vault is very spherical, like modern humans'."
(Related: Make "missing links" morph with the National Geographic Channel's interactive on extreme evolution.)
The African fossil record from the Gawis skull's time period is sparse, and most of the specimens are poorly dated, scientists said.
"The evolutionary period between Homo erectus and Homo sapiens is confused," said Andrew Hill, curator of anthropology at Yale University's Peabody Museum of Natural History in New Haven, Connecticut.
"The Gawis cranium is almost certain to provide very useful information."
Between 0.8 million years ago, when Homo erectus went extinct, and about 200,000 years ago, one or more species existed in Africa that gave rise to the earliest members of Homo sapiens, our own species.
"There are at least one to three species of Homo recognized within that time period. But we don't know exactly what the relationship is of any of those to modern humans," said Eric Delson, a paleoanthropologist at Lehman College of the City University of New York. Delson was not involved in the discovery.
"This specimen doesn't seem to show any specific features like modern humans', but it's much more lightly built than Homo erectus," Delson added.
Simpson, the project paleontologist, says the anatomical change seen in the Gawis skull represents humanity's transition to anatomical modernity in Africa.
"We're on the cusp of this middle Stone Age archaeological transition where people are beginning to have a better handle on how to create more delicate tools and human anatomy is reflecting this with the brain being reorganized like modern humans'," he said.
"We are not modern humans yetwe really don't see that coming on until 200,000 years agobut we're certainly on the way to making it," Simpson added.
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