A battered fossil leg bone discovered more than 20 years ago in Chad is finally making its scientific debut. Researchers say that the remains, described today in Nature, show that a species called Sahelanthropus tchadensis was an ancient human relative that walked on two feet1.

At seven million years old, S. tchadensis is a candidate for the earliest known member of the hominin lineage — the evolutionary branch that leads from the common ancestor of humans and chimpanzees to modern humans.

A French and Chadian team discovered S. tchadensis in July 2001, during an expedition in the Lake Chad basin. The key find was a nearly complete, but heavily damaged, skull that was described in Nature the following year2.

“It is great that these specimens are finally published officially, since their presence has been known to a lot of us,” says Yohannes Haile-Selassie, a palaeoanthropologist at Arizona State University in Tempe. He says the description “clearly shows that the femur assigned to Sahelanthropus here had most of the morphology that one would expect to see in a habitual biped”, and confirms that Sahelanthropus was a hominin.

“The Sahelanthropus femur doesn’t have ‘smoking-gun’ traces of bipedalism,” writes Daniel Lieberman, a palaeoanthropologist at Harvard University in Cambridge, Massachusetts, in an essay accompanying the paper4, “but it looks more like that of a bipedal hominin than that of a quadrupedal ape.”

Still, Macchiarelli thinks Sahelanthropus is more likely to be an ape than a hominin, and one that lived not long after the two lineages diverged, in the past ten million years.