Analysis of the fossilized hands and feet of an early human ancestor discovered in a South African cave suggests an "all-rounder," happy to walk on the ground but adept at taking to the trees when necessary.
The feet of Homo naledi show adaptations that made them suitable for walking on open ground, while the hands retained more ape-like curved fingers for grasping and holding onto tree branches, researchers say.
"Homo naledi's foot is far more advanced than other parts of its body, for instance, its shoulders, skull, or pelvis," says William Harcourt-Smith from the division of paleontology at the American Museum of Natural History.
"Quite obviously, having a very human-like foot was advantageous to this creature because it was the foot that lost its primitive, or ape-like, features first," he explains.
That is evidence of the kinds of selective evolutionary pressures Homo naledi was facing, he says.
One of the defining properties of the entire human lineage is walking upright, and researchers report in the journal Nature Communications of finding specimens of almost every single bone in the foot of the newly-discovered species, which tells a lot about how it moved about.
It shares many features with a modern human foot, suggesting early adaptations for standing erect and walking on two feet, they say.
"You can imagine that during the day, when it was out and about, it was mostly on the ground," explains Harcourt-Smith. "But for things like going to feed or to hide from predators, it would have gone into the trees, because we see that it has retained some of these more primitive features in the foot. So: much more bi-pedal than not, but not 100 percent."
In a separate study on H. naledi hand bones found at the same South African site, including a complete adult right hand, researchers noted anatomical features not seen previously in any fossil of an early human ancestor.
The hands share features with later Neanderthal and human hands that suggest both powerful grasping and the ability to use stone tools, the researchers report.
"The features that we see particularly in the wrist, we've only ever found in Neanderthals and [modern humans], and we know that those are committed to using tools," says Tracy Kivell from Kent University in Britain.
"Perhaps naledi was using tools that were made out of different materials or doing some other forceful, precision-grip manipulations, but the most straight-forward explanation is that naledi is making and using tools," she says.
