Seven-million-year-old femur suggests Sahelanthropus tchadensis walked upright

An ancient human relative, Sahelanthropus tchadensis, might have walked on two legs seven million years ago. S. tchadensis could be the earliest known member of the hominin lineage, the evolutionary branch that includes the common ancestor of humans and chimpanzees and ends with modern humans. The theory is based on a battered fossil leg bone that was discovered in Chad more than 20 years ago. But some scientists are not convinced that the femur’s traits prove the creature stood tall.