There is only one really good fossil of this Homo rudolfensis: KNM-ER 1470, from Koobi Fora in the Lake Turkana basin, Kenya. It has one really critical feature: a braincase size of 775 cubic centimeters, which is considerably above the upper end of H. habilis braincase size. At least one other braincase from the same region also shows such a large cranial capacity.
Originally considered to be H. habilis, the ways in which H. rudolfensis differs is in its larger braincase, longer face, and larger molar and premolar teeth. Due to the last two features, though, some scientists still wonder whether this species might better be considered an Australopithecus, although one with a large brain!