Scientists had previously believed the upright posture we have today originated six million years ago in Africa.
But the fossils of a previously unknown primate named Danuvius, discovered in southern Germany, suggest apes were displaying the human-like characteristics long before then.
The team, led by Madelaine Böhme from the University of Tübingen, worked in a clay pit in Bavaria, where they excavated more than 15,000 vertebrate bones.
Remains of at least four individual primates were found, and the most complete skeleton — of a male Danuvius — is similar in size and shape to modern-day bonobos. His preserved limb, finger and toe bones helped the scientists reconstruct how he moved in his environment.
“The finds in southern Germany are a milestone in paleoanthropology, because they raise fundamental questions about our previous understanding of the evolution of the great apes and humans,” she added.
“In contrast to later hominins, Danuvius had a powerful, opposable big toe, which enabled it to grasp large and small branches securely,” said Nikolai Spassov of the Bulgarian Academy of Science, who contributed to the study.
Danuvius stood about a meter (3.3 feet) in height and weighed less than most apes today. Males measured at around 31 kilos (68 pounds), and females at about 18 kilos (40 pounds).
“The ribcage was broad and flat, and the lower back was elongated; this helped to position the center of gravity over extended hips, knees and flat feet, as in bipeds,” said a press release from the University of Tübingen.