A new set of papers describing the hand and foot functions of Homo naledi has revealed that our newly-found relative may have been uniquely adapted for both tree climbing and walking as dominant forms of movement, while also being capable of precise manual manipulation.
According to the researchers, this indicate a decoupling of upper and lower limb function in H. naledi, providing an important insight into the skeletal form and function that may have characterised early members of the Homo genus.
An international team of researchers recovered some 1,550 fossil elements from a cave in the Cradle of Humankind World Heritage Site, some 50 km northwest of Johannesburg.
Lead author William Harcourt-Smith from University of the Witwatersrand in South Africa describes H naledi’s foot based on 107 foot elements from the Denaldi Chamber, including a well preserved adult right foot.
“H naledi foot shares many features with a modern human foot, indicating it is well-adapted for standing and walking on two feet. However, it differs in having more curved toe bones,” Harcourt-Smith noted.
Another lead author 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 hand reveals 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,” Kivell pointed out.
However, the finger bones are more curved than most early fossil human species, suggesting that H naledi still used their hands for climbing in 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.
“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,” Kivell described.
The papers published in the scientific journal Nature Communications.