In "P. boisei", the jaw hinge was adapted to grinding food side-to-side (rather than up-and-down in modern humans), which is better at processing the starchy abrasive foods that likely made up the bulk of its diet. "P. robustus" may have chewed in a front-to-back direction instead, and had less exaggerated (less derived) anatomical features than "P. boisei" as it perhaps did not require them with this kind of chewing strategy. This may have also allowed "P. robustus" to better process tougher foods.