|SK 48 - P. robustus|
In a recent article in PNAS, Villmoare and Kimbel take a fresh look at this debate by analyzing CT scans of several species of gracile and robust australopithecines. They focused on a feature called the anterior pillar, a ridge of bone running vertically down the side of the nose. This feature has been argued to be a shared derived trait linking the South African hominins P. robustus (robust) and A. africanus (gracile). The anterior pillars of P. robustus and A. africanus turn out to be quite different when viewed internally. Furthermore, the internal structure of P. robustus is very similar to the structure of P. boisei, an east African robust, even though P. boisei usually lacks the visible external anterior pillar. The authors interpret these findings as additional evidence that the eastern and southern robusts are a natural group, and that the superficial resemblances between P. robustus and A. africanus are the result of parallel evolution.