Various primate bones
Left: 3D models of Sahelanthropus tchadensis bones. The femur (upper leg bone) is on the left, shown in posterior and medial views. The right and left ulnae (forearm bones) are next, presenting anterior and lateral views. Right: modeling demonstrating cortical thickness of femurs, which helps researchers infer the method of locomotion. From left to right: S. tchadensis, extant human, chimpanzee, and gorilla
Franck Guy / PALEVOPRIM / CNRS – University of Poitiers

One of the most prominent adaptations in hominin evolution has been the ability to walk upright on two limbs. A study published today (August 24) in Nature has revealed that bipedalism was likely on the scene one million years earlier than previously known. Researchers in France modeled the femur and ulnae of a member of the species Sahelanthropus tchadensis, the oldest known human representative, that lived in Chad 7 million years ago and compared those bones to corresponding skeletal features in modern humans, chimpanzees, and gorillas. 

The authors find that while the femur suggests S. tchadensis was capable of bipedalism, the morphology of the ulnae indicates it also very likely spent time in trees and was able to traverse both worlds.

The researchers dedicated the study to Yves Coppens, the French paleontologist who found hominin bones in Chad in the 1960s and, most famously, co-discovered the remains of the Australopithecus afarensis nicknamed “Lucy”. Coppens died in June.