A well-preserved skull of an early human found in the northeast African country of Eritrea will help plug a major gap in the fossil record of human evolution. Dated to 1 million years ago, the skull shows a tantalizing mix of ancient and modern features, says Ernesto Abbate, a geologist at the University of Florence in Italy and head of the multinational team that reports the discovery in tomorrow's Nature.
The skull was found in remote, arid lands about 400 kilometers north of the Awash Valley in Ethiopia, famed for its human fossils. The nearly complete brain case resembles that of Homo erectus, a human ancestor that appeared in Africa 1.7 million years ago and is found in Asia until as recently as 30,000 years ago. Like H. erectus, the skull has a pronounced brow ridge and elongated brain case, among other features, says Lorenzo Rook, a paleontologist at the University of Florence.
To date the stratum where it was found, the team looked in the rocks for the signature of known reversals in Earth's magnetic field and identified fossils from mammals that went extinct at known times. The resulting age of 1 million years puts the fossil right between the youngest H. erectus found in Africa--a 1.4-million-year-old fossil from Olduvai, Tanzania--and the oldest archaic form of H. sapiens, a 600,000-year-old specimen from Bodo, Ethiopia.
A closer look at the fossil revealed modern-looking features mixed with the old. The skull is remarkably narrow, reaching its greatest width near the top, as in H. sapiens. This suggests that some traits typical of H. sapiens had begun to develop 200,000 to 300,000 years earlier than expected, says Rook.
Ultimately, the fossil could help anthropologists make sense of other fossils found outside Africa that fall in the critical time gap, such as 800,000-year-old remains at Atapuerca, Spain, and H. erectus in Asia. "This is clearly going to be a major player in future scenarios, but it has to be studied," says Ian Tattersall, a paleoanthropologist at the American Museum of Natural History in New York. The skull--half of which is still embedded in rock--has been kept under wraps at the Eritrea National Museum in Asmara.