Researchers, led by Georgian National Museum anthropologist David Lordkipanidze, first found the complete lower jaw of a fossil human in 2000. The cranium turned up five years later, at the fossil-rich Dmanisi site 96 miles southwest of Tbilisi, and is now being reported in the journal Science.

"It was discovered on August 5, 2005—in fact, on my birthday," Lordkipanidze says. He adds that the fossil's importance was clear as soon as the team saw it, but required eight years of preparatory analysis.

That is because Skull 5 is what paleoanthropologists often refer to as a "mosaic," or mixture of features seen in earlier and later humans. The skull's face, large teeth, and small brain size resemble those of earlier fossil