Homo naledi Updates: Arms, Legs, & More on the Skull!

Lee Berger team, wikicommons

While many of us were reeling from recent political events, the Homo naledi team was quietly flooding us with new information about one of the most interesting hominin species of all time. As many of you will remember, naledi was announced in 2015, after being found deep in a cave in South Africa. From the beginning, it was clear that naledi was a crazy amalgamation, a mixed mosaic of recent features seen in modern humans, primitive traits seen on only our most ancient of ancestors, and unique traits never before seen in fossil hominins.

In 2015, we learned about aspects of naledi such as the hand and foot. We saw that naledi’s hand was capable of fine manipulation needed for tool use, and her foot showed evidence of bipedal walking. Now, we have a closer look at three separate body parts: the arm, leg, and mandibles. A reminder that there isn’t yet a date for the naledi fossils, but scientists can still study the bones to see which other hominins they resemble most closely. A second reminder that many individuals were found in this cave, so the bone fragments represent quite a few naledi individuals. So what’s new with our favorite small brained, modern handed creatures? Here is a very brief overview:

1. Naledi’s arm. The team examined 90 bone fragments from the shoulder (scapula and clavicle) and the upper and lower arm of naledi. They found that, overall, the shoulder and upper arm (humerus) was much more primitive than the lower arm (radius and ulna). The shoulder, in particular, is reminiscent of Australopithecus. This upper arm configuration suggests that naledi were certainly competent climbers, a skill that was lost by the time modern humans emerged. But what about the potential for tool use? The authors argue that the potential is there, especially when we consider the previously described hand of naledi, which shares many traits with modern humans and Neanderthals.
2. Naledi’s leg. The team examined 108 bits of bone from the upper leg (femur), the kneecap, and the lower leg (tibia and fibula), finding continued evidence of a mixture of primitive, derived, and unique traits. Interestingly, the authors saw evidence for adaptations for long distance walking and possibly running. Naledi’s femur appears to share a number of traits with various species of Homo, including a longer “neck” and a strong attachment site for the gluteus maximus muscle. However, the femural fragments, along with the lower leg bones, also showed traits seen in Australopiths. Match this mosaic with the relatively modern foot of naledi, and you certainly have an interesting picture of a hominin who could likely cover long distances.
3. Naledi’s skull. In a look at 41 new bits of skull–both crania and jaw fragments–the team found that the naledi skull shares many traits with members of the genus Homo. Naledi’s face and jaw, in particular, has many Homo-like traits– despite the fact that naledi had a very small brain (a trait that was once highlighted as the defining marker for inclusion in the genus). One other cool aspect of this study is that they examined the jaw of a child.

What does all this tell us? 

Naledi’s leg and arm fit well with what we see in the foot and hand. All of these body parts seem to support the mosaic nature of naledi, contributing to the mystery and intrigue surrounding fossil species. Overall, the Naledi team see the bones’ anatomy as consistent with a transition from Australopithecus to early Homo, but further work will continue to examine and test this hypothesis.

As naledi team member John Hawks wrote recently, we just don’t know where naledi fits in the human family tree yet (or better yet–the human braided steam–?–we’ll have to workshop that phrase). Everyone is hoping for a date on the fossils, which will provide another data point against which scientists can test their hypotheses.

P.S. A fourth study was also published this week, examining the skull diversity in Homo to ascertain naledi’s position within the genus. Time permitting, I hope to look into that study in the near future, as well as delve deeper into the details of the studies discussed here! Cheers to the researchers analyzing this crazy assemblage of bones, I look forward to hearing more in the future! The new papers (unfortunately, not open access):

1. Marchi D., et al., The thigh and leg of Homo naledi, Journal of Human Evolution (2016), http://dx.doi.org/10.1016/j.jhevol.2016.09.005
2. Feuerriegel E., et al., The upper limb of Homo naledi, Journal of Human Evolution (2016), http://dx.doi.org/10.1016/j.jhevol.2016.09.013
3. Laird, M.F., et al., The skull of Homo naledi, Journal of Human Evolution (2016), http://dx.doi.org/10.1016/j.jhevol.2016.09.009
4. Schroeder, L., et al., Skull diversity in the Homo lineage and the relative position of Homo naledi, Journal of Human Evolution (2016), http://dx.doi.org/10.1016/j.jhevol.2016.09.014