Scientists have found that 7 million years ago, ancient human ancestors began to walk on two legs

The conclusions are based on a detailed analysis of the fossils of the thigh (femur) and forearm (ulna) of the oldest representative species of man, Sahelanthropus chadensis. The fossils were first discovered in 2001 in Toros-Menalla, Chad.

At the same time, these early hominids likely also climbed trees on all four legs—as you would expect if the species gradually went from four to two.

“Here, we present postcranial evidence of locomotor behavior in the Shah of Chad, providing new insights into bipedalism in the early stages of hominin evolutionary history,” the researchers wrote in their published paper.

By comparing the fossilized thigh and forearm with equivalent bones from humans, chimpanzees and gorillas, the researchers were able to figure out how they were used and how the species moved (its “movement patterns”).

Above: 3D model of the Chad Shah Fossil.

The researchers studied 20 different features of these fossil bones to determine whether the Chad Shah walked on two or four legs, including the external shape and internal structure of the remains, as assessed by microtomography.

They concluded that the most likely scenario was “habitual bipedalism” and sometimes tree climbing.

The team also noted that these species climbed trees differently than today’s gorillas and chimpanzees: They gripped tightly rather than relying on the bones of their fingers and toes.

“The curvature and cross-sectional geometry of the ulna…indicate habitual arboreal behavior, including climbing and/or ‘careful climbing,’ rather than terrestrial tetrapods,” the researchers wrote.

The research builds on an earlier study of a fossilized skull unearthed at the same site, which is also thought to belong to the Chad Shah. Skull analysis suggested that these ape-like creatures were bipedal, but now there is more comprehensive evidence.

Above: Restoration of the Chad Shah Skull.

These fossils date back (6 to 8 million years ago) when humans were genetically separated from chimpanzees and bonobos, our closest living relatives, so this is a crucial stage, It is also a stage that has attracted a lot of scientific debate.

These early hominins likely lived in a mix of forests, palm groves and grasslands, and walking on two legs and climbing trees were their options for finding food and water.

“The most conservative hypothesis remains that the postcranial morphology of the Chadian Shah suggests bipedalism, and any other hypothesis would not have much explanatory power for the set of features presented by the Chadian material,” the researchers wrote.

The research was published in the journal Nature.