KNM-ER 406 is a nearly complete adult male Paranthropus boisei. It has the facial and cranial features typical of the species such as massive cheek teeth, and the widely flaring zygomatic arches with a forward placed connection to the other facial bones, and large cheek bones supported powerful chewing muscles - the latter two features giving it a "dish-shaped" face. Other muscles extended from his jaw to the sagittal crest at the top of his head. The cranial capacity of this skull has been estimated at 510 cubic centimeters.
P. boisei commonly ate fruit and other soft foods. But these early humans were also able to crush and grind tough plant foods during difficult times.