The discovery of a 3.5-million-year-old hominid skull and other fossil remains in northern Kenya is shaking the human family tree at its very roots. The new find shows that this bushy tree started sprouting branches even earlier than researchers had realized.
Hominid evolution had seemed relatively simple between 3 million and 4 million years ago. After decades of searching, most researchers had concluded that Australopithecus afarensis, whose best known member is the partial skeleton "Lucy," was the only clearly identified hominid in Africa at that time. Winding the clock back farther, a 4-million-year-old australopithecine, A. anamensis, seemed a likely ancestor to Lucy. But the new discovery, dated smack in the middle of this critical million years, could put a kink into any straight-lined phylogeny, because it doesn't share key features with either A. afarensis or A. anamensis.
The new hominid bones were discovered in 1998 and 1999 by a team led by Meave Leakey of the National Museums of Kenya in Nairobi. The team uncovered an almost complete cranium, as well as a bone from the temple, parts of two upper jaws, and assorted teeth. She and her colleagues now unveil the reconstructed skull in the 22 March issue of Nature. The new hominid was dubbed Kenyanthropus platyops, "the flat-faced man of Kenya." Notably, it has a small braincase and small molars set in a large, flat face--characteristics never before found together in one skull. In contrast, A. afarensis, the only other hominid known from this period, has large molars and a much smaller, projecting face.
Experts are unanimous that the find will complicate efforts to trace the convoluted course of human evolution. Indeed, experts say the importance of the new discovery lies in its demonstration that the roots of the human evolutionary tree are pretty tangled. "Those of us who have been suggesting that human evolution is more like a bush than a ladder," says Bernard Wood of George Washington University in Washington, D.C., "may not have been far off the mark."
The Paleontology Department of the National Museums of Kenya