Homo naledi adapted to both tree climbing, walking upright

Johannesburg: The newly discovered human ancestor Homo naledi may have been 'jack of all trades' - uniquely adapted for both tree climbing and walking upright, while also being handy with tools, new research has found.

Two new studies describing the structure and function of the Homo naledi hand and foot indicate the species may have been uniquely adapted for both tree climbing and walking as dominant forms of movement, while also being capable of precise manual manipulation.

The research was conducted by a team of international scientists associated with the University of the Witwatersrand in South Africa, home of the Rising Star Expedition team that have since the 2013-discovery of the largest hominin find yet made on the African continent, recovered some 1,550 numbered fossil elements from a cave in the Cradle of Humankind World Heritage Site.

The research indicates a decoupling of upper and lower limb function in H naledi, and provides an important insight into the skeletal form and function that may have characterised early members of the Homo genus.

Lead author of one study William Harcourt-Smith and colleagues describe the H naledi foot based on 107 foot elements from the Denaldi Chamber, including a well preserved adult right foot.

They show the H naledi foot shares many features with a modern human foot, indicating it is well-adapted for standing and walking on two feet. However, the authors note it differs in having more curved toe bones (proximal phalanges).

Lead author of the second study Tracey Kivell and colleagues describe the H naledi hand based on nearly 150 hand bones from the Denaldi Chamber, including a nearly complete adult right hand (missing only one wrist bone) of a single individual, which is a rare find in the human fossil record.

The H naledi hand shows a unique combination of anatomy that has not been found in any other fossil human before.

The wrist bones and thumb show anatomical features that are shared with Neanderthals and humans and suggest powerful grasping and the ability to use stone tools.

However, the finger bones are more curved than most early fossil human species, such as Lucy's species Australopithecus afarensis, suggesting that H naledi still used their hands for climbing the trees.

This mix of human-like features in combination with more primitive features demonstrates that the H naledi hand was both specialised for complex tool-use activities, but still used for climbing locomotion, researchers said.

"The tool-using features of the H naledi hand in combination with its small brain size has interesting implications for what cognitive requirements might be needed to make and use tools, and, depending on the age of these fossils, who might have made the stone tools that we find in South Africa," said Kivell.

The research was published in the journal Nature Communications.