For instance, the extremely heavy jaws and thickly enameled teeth of Paranthropus robustus suggest that, when times were lean, it was capable of subsisting on low-quality foods that were difficult to chew. Moreover, some of the skulls and teeth of Paranthropus robustus are exceptionally large, while others are robust but not as large as those in the first group.

This suggests that Paranthropus robustus was characterized by larger males and smaller females, indicating a mating system called polygyny, in which a single dominant male mates with multiple females.

Unfortunately, Swartkrans has over the years yielded many fewer bones from the rest of the Paranthropus robustus skeleton, limiting our understanding of its stature, posture, and locomotion, essential characteristics related to finding food and mates. A major new find from Swartkrans, the first articulating hipbone, thigh bone, and shin bone of Paranthropus robustus, changes that.

A team of international researchers affiliated to the Evolutionary Studies Institute at the University of the Witwatersrand (Wits University) in South Africa, including Travis Pickering, Matthew Caruana, Marine Cazenave, Ron Clarke, Jason Heaton, A.J. Heile, Kathleen Kuman, and Dominic Stratford, has discovered that this group of fossils belongs to a single, young adult Paranthropus robustus.

The fossil not only demonstrates that the species was, like modern humans, a habitual upright walker, but also confirms it was also extremely small. The research is published in the Journal of Human Evolution.