Research highlight: Pelvic fragment from the Lesedi Chamber

Citation: Cofran, Zachary, Caroline VanSickle, Reynaldo Valenzuela, Daniel García-Martínez, Christopher S. Walker, John Hawks, Bernhard Zipfel, Scott A. Williams, and Lee R. Berger. The immature Homo naledi ilium from the Lesedi Chamber, Rising Star Cave, South Africa. American Journal of Biological Anthropology https://doi.org/10.1002/ajpa.24522

Homo naledi has a very large fossil sample from the Dinaledi Chamber, including more than 40 fossils representing the pelvis. However, those fossils are very highly fragmented and come from several different individuals of different ages. That means our knowledge of the pelvic anatomy of H. naledi is incomplete.

The Lesedi Chamber is best known for the Neo skeleton, which is the most complete single individual of H. naledi that our team has reported so far. But there are also remains of at least two other individuals from this chamber. One of the hominin fossils that cannot belong to the Neo skeleton is an immature partial ilium, U.W. 102a-138. In this paper, led by Zach Cofran from Vassar College, our team examines this pelvic fragment to assess its age and consider what it can tell us about H. naledi and its locomotion.

Based on our comparisons, this ilium represents an individual likely between 4 and 11 years of age, in human standards. The size and developmental stage of the ilium is similar to two juvenile ilia from Makapansgat, MLD 7 and MLD 25, both attributed to Australopithecus africanus. Broadly, the anatomy of the Lesedi ilium is similar to these Au. africanus fossils. In particular, the shape of the iliac blade is more like MLD 7 than it is like the ilia of living human children across this range of ages.

There is one main difference between the H. naledi and Au. africanus ilia, and that is the relatively large sacroiliac joint area in H. naledi. This is a humanlike feature of the pelvis in H. naledi, and the Lesedi fossil confirms this morphology in the most complete ilium we have found so far. What it means is less clear, and right now Erica Noble, a PhD student in my lab, is investigating the question further with comparisons of human and great ape ilium morphology.