Tiny bump on 7 million-year-old fossil suggests ancient ape walked upright — and might even be a human ancestor

Chimpanzee skull with ulnar and femur, Sahelanthropus tchadensis skull with ulnar and femur, and human skull with ulnar and femur.

The discovery of a never-before-seen bump on the leg bone of a 7 million-year-old fossil ape shows it walked upright on two legs while it was on the ground, a new study finds.

Only members of the human lineage have this lump, called the femoral tubercle. That makes the species, Sahelanthropus tchadensis, the earliest known hominin, according to the study, published Jan. 2 in the journal Science Advances. (Hominins are the group of species, including humans, that existed after the split from chimpanzees and bonobos. Walking upright on two legs is a defining characteristic of hominins.)