Bili ape skulls have the prominent brow ridge and may sometimes have a sagittal crest similar to that of a gorilla, but other morphological measurements are more like those of chimpanzees. Only one of the many skulls found at Bili had a sagittal crest, thus it cannot yet be considered typical for the population. Chimpanzee skulls are 190 to 210 millimeters long, but four out of five Bili ape skulls measured more than 220 millimeters, well beyond the end of the normal chimpanzee range.