Only a decade ago, the earliest known human ancestor was a species whose most famous member, Lucy, lived in east Africa about 3.2 million years ago. But in July, the nearly complete cranium of a primate that lived twice as long ago--between 6 million and 7 million years ago--was introduced as the oldest known hominid, the lineage that includes humans but not other apes. This fossil, found by a team of French and Chadian researchers, fills a crucial gap at the dawn of human evolution when almost nothing is known; the next oldest published hominid skull is almost 3 million years younger.
It also is important because it was found in an unexpected place: along the shores of the ancient Lake Chad in western Africa. Until now, the earliest ancestors of the human family were found in east Africa, which has been called the cradle of humanity.
The fossil, nicknamed Toumaï for "hope of life" in the Goran language, shows that the earliest hominids were more widely distributed across Africa than previously thought, and it challenges old views about where the first hominid arose.
At this early age, Toumaï looks most like an ancient ape, with a brain the size of a chimpanzee's, large incisors, and widely spaced eyes like those of a gorilla. But the shape and size of its canines and lower face resemble those of human ancestors that came later; it has small, unsharpened canines and a flat lower face, unlike the protruding snout of living apes. The mix of features convinced the fossils' discoverers that they had found a new genus and species of hominid, which they named Sahelanthropus tchadensis.
Controversy is another prominent feature of these fossils. A competing team of researchers (who have discovered another, slightly younger fossil that they say is the earliest hominid) argues that Toumaï is the ancestor of an extinct ape or gorilla, partly because there are no skeletal bones to show whether it walked upright--the hallmark of being a hominid. Others who have seen the skull, however, disagree. Although detailed analysis has just begun, they say that on the face of it, Toumaï looks like a hominid.