From ScienceDaily:
A new study that for the first time examined the internal anatomy of a fossil human relative’s heel bone, or calcaneus, shows greater similarities with gorillas than chimpanzees.
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In doing this, the team revealed new insights into how our ancestors moved through and interacted with their environment approximately 2-2.5 million years ago. Similarities between the fossil from Sterkfontein and gorillas indicate that Australopithecus africanus, the species of human ancestor (or hominin) also represented by the Taung Child, or at least this individual member of the species, exhibited gorilla-like levels of joint mobility and structural reinforcement.
Results of the new study were surprising because other recent studies of the australopithecine calcaneus, focusing on its external anatomy, have emphasised similarities with chimpanzees or humans. Paper. (paywall) – Angel Zeininger, Biren A. Patel, Bernhard Zipfel, Kristian J. Carlson. Trabecular architecture in the StW 352 fossil hominin calcaneus. Journal of Human Evolution, 2016; 97: 145 DOI: 10.1016/j.jhevol.2016.05.009 More.
An alternative thesis might be that we don’t know much about it at all. 
See also: Gorilla y chromosome closer to human than chimp
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