The cranial vault

The curvature and components of the vault

(1) The parieto-occipital plane of Zinjanthropus rises steeply from the external occipital protuberance. The vault of Australopithecus is more evenly curved in this area.

(2) The parietotemporal side-walls of the vault also rise steeply, contributing to the full, rounded character of the vault. This feature finds a parallel in the latest cranium of Australopithecus from Makapansgat, MLD 37/38.

(3) The vault of Zinjanthropus, as seen in norma verticalis, is long-spheroid, whereas that of the reconstructed Paranthropus is short-spheroid and that of Australopithecus long-ovoid. Zinjanthropus is intermediate in this respect between the two South African forms, though approaching more closely to the second reconstruction of Paranthropus.

(4) Most dimensions of the parietal bones in Zinjanthropus fall within the range of variation of Australopithecus, while a few dimensions exceed the range. In anteroposterior extension, the australopithecine parietal is slightly smaller than that of Homo erectus, whereas, in mediolateral extension, the australopithecine parietal is far smaller than that of H. erectus. In contradistinction, the anteroposterior extent of the parietal bone in pongids is far smaller than in australopithecines.

(5) The chord-arc indices of the edges of the parietal bones show that in Zinjanthropus, the parietal bone is slightly less curved along the coronal margin than in Australopithecus. The anteroposterior curvature of the parietal bones of Australopithecus tends to be greater, and the mediolateral curvature less, than in H. erectus.