Robust australopithecines are characterised by heavily built skulls capable of producing high stresses and bite forces, and some of the largest molars with the thickest enamel of any known ape. "P. boisei" is the most robust of this group. Brain size was about , similar to other australopithecines. Some skulls are markedly smaller than others, which is taken as evidence of sexual dimorphism where females are much smaller than males, though body size is difficult to estimate given only one specimen, OH 80, definitely provides any bodily elements. The presumed male OH 80 may have been tall and in weight (assuming improbable humanlike proportions), and the presumed female KNM-ER 1500 tall (though its species designation is unclear). The arm and hand bones of OH 80 and KNM-ER 47000 suggest "P. boisei" was arboreal to a degree and was possibly capable of manufacturing tools.