IMAGE, PETER SCHMID AND WILLIAM HARCOURT-SMITH | WITS UNIVERSITYHomo naledi may have been just as adept at swinging through the tree tops as striding across the ground, according to two new studies of fossil remains from the recently discovered human relative. Reporting their results in Nature Communications today (October 6), two international teams studied a H. naledi fossil hand and foot recovered from the cave 50 kilometers northwest of Johannesburg, where scientists unearthed the remains of 15 individuals belonging to the new species in 2013. The teams found that H. naledi’s hands had the wrist morphology and the long, robust thumbs common to Neanderthals and modern humans, while the human ancestor had longer, more curved fingers, typical of primates that swing and hang from tree branches or rocks. The species’ feet, however, had a predominantly modern human-like structure, suggesting that H. naledi was also bipedal.
The authors of the hand paper suggested that the modern human-like aspects of H. naledi’s hand morphology meant it likely manipulated objects with a precision grasp and may have used tools. “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,” study coauthor Tracy Kivell of Kent University in the U.K. told BBC News. “They make tools, complex tools, and use them all the time, enough so that it's actually changed their morphology. 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.”
The researchers who studied 107 fragments of H. naledi foot bones—including one nearly-complete adult foot—also found a mixture of modern and primitive features. While the foot fossils contained features of modern human feet, it also had elongated and curved toes, suggesting that the five-foot-tall species spent at least some time among the treetops. “It was unequivocally spending more time walking upright than not,” study coauthor William Harcourt-Smith of Lehman College at the City University of New York and the American Museum of Natural History told The Guardian. “But you can imagine it spending time in the trees to gather fruit, or perhaps nesting in trees, or going there when there are predators around.”
As the fossil-rich South African cave continues to give up its secrets to busy paleoanthropologists, a more complete picture will emerge of our 4 million-year-old relative will emerge. For now, it’s becoming clear that H. naledi was by no means a one-dimensional hominin. “Regardless of age, this species is going to cause a paradigm shift in the way we think about human evolution, not only in the behavioral implications—which are fascinating—but in morphological and anatomical terms,” Harcourt-Smith said in a statement.