On 15 August 1959 the first announcement of the discovery of a new fossil cranium from Olduvai appeared in Nature (Leakey, 1959a). A week later, on Saturday 22 August 1959, at the formal opening ceremony of the fourth Pan-African Congress on Prehistory in Léopoldville, Dr L. S. B. Leakey publicly announced to the astonished and enthusiastic delegates more details of the important new specimen (Tobias, 1960a). He reiterated his view, expressed already in Nature, that the big-toothed cranium was that of a young male, representing a new genus of the subfamily Australopithecinae. To this genus he gave the name Zinjanthropus, Zinj being ‘the ancient name for East Africa as a whole’. He enumerated twenty features in which he claimed the new specimen differed from members of either of two previously-recognised australopithecine genera, Australopithecus and Paranthropus. He went on to designate the species as Zinjanthropus boisei sp.nov., the specific name being in honour of Mr Charles Boise, whose generous financial help had made the discovery possible. Leakey's (1959a) preliminary diagnosis of its specific features reads as follows: ‘A species of Zinjanthropus in which the males are far more massive than the most massive male Paranthropus. The face is also excessively long. Males have a sagittal crest, at least posteriorly. Upper third molars smaller than the second.’

Leakey stressed the tentative nature of his generic and specific diagnosis, recognising that, if and when further material were found, ‘the diagnosis will need both enlarging and possibly modifying’.