Homo rudolfensis skull KNM-ER 1470 (1.8 to 1.9 million years).
The Homo rudolfensis skull KNM-ER 1470 was discovered by B. Ngeneo in 1972 at Koobi Fora in Kenya and described by R. Leakey in Nature in 1973. The classification of this specimen has been a matter of debate since its discovery, with some scientists arguing in favour of Australopithecus, and some in favour of a species of Homo. Originally dated (incorrectly) a million years before habilis, the most current theory holds that though contemporaneous and geographically concurrent with habilis, this specimen is in fact a different species of Homo. Homo rudolfensis skull KNM-ER1470 features a 750cm3 braincase, too large for australopithecines, and perhaps even for habilis, and lacks the crests and heavy muscle markings that characterize australopithecine skulls, as well as lacking the brow ridges associated with Homo erectus. Several features differ from other habilis specimens (a longer face, squared upper jaw and short, shallow palate), leading some scientists to conclude that there is too great a range of characteristics within the specimens for them to be a single species. In 1986 Valerii Alexeev proposed another species within Homo, giving 1470 the scientific name Homo rudolfensis. A photograph of this specimen was used on the cover of Leakey and Lewin's book Origins.