A. robustus and A. boisei had large, massive molars. These are significantly larger than earlier hominid molars. The incisors also were relatively small. The jaw was relatively boxy in appearance. Electron microscope examination of the wear on the teeth indicates that the diet was composed of hard plant fibers and grit.

Human jaws can generate around 400 pounds of bite force but robust australopithecines could have exceeded 1,700 pounds. It was a specialized diet of high fiber that led to this dramatically well developed jaw along with the massive molars.

Contrast the size of robust australopithecine teeth, particularly the back molars, with those of modern humans. Any dentist alive today would marvel at these!

LOOK AT THESE LARGER THAN LIFE TEETH!

The robust forms had a massive mandible (jaw) for grinding with such force. Here we can see the size and examine how muscles may have wrapped downward from the sagittal crest to that massive mandible.

The front of face was equally massive to help buttress the muscle structure. As a comparison, feal where your muscles are located on your head as you move your jaw up and down as if you were chewing something rather tough and fibrous.

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