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Archaic Hominins

This grade includes all of the remaining unambiguously hominin taxa not conventionally included in Homo and Paranthropus (see below). The first taxon to be recognized in this grade was Australopithecus africanus Dart 1925. The type specimen, Taung 1, a juvenile skull with a partial natural endocast, was recovered in 1924 from the limeworks at Taung (formerly Taungs), now in South Africa. Most of the other fossil evidence for Au. africanus comes from two caves, Sterkfontein and Makapansgat, with other evidence coming from the Gladysvale cave. Unless the associated skeleton StW 573 from Mb 2 (Clarke, 2008) and 12 hominin fossils recovered from the Jacovec Cavern (Partridge et al., 2003) expands it, the temporal range of Au. africanus is ca. 3–2.4 Ma. The cranium, mandible, and the dentition are well sampled; the postcranial skeleton, and particularly the axial skeleton, is less well represented, but there is at least one specimen of each of the long bones, but many of the fossils have been crushed and deformed by rocks falling on the bones before they were fully fossilized. The picture that has emerged from morphological and functional analyses suggests that although Au. africanus was capable of walking bipedally it was probably more arboreally adapted (i.e., it was a facultative and not an obligate biped) than other archaic hominin taxa, such as Australopithecus afarensis. It had relatively large chewing teeth, and apart from the reduced canines the skull is relatively ape-like. Its mean endocranial volume is ca. 460 cm3. The Sterkfontein evidence suggests that males and females of Au. africanus differed substantially in body size but probably not to the degree they did in Au. afarensis.

The taxon Au. afarensis Johanson, White, and Coppens 1978 is only known from East African sites. The type specimen is an adult mandible, LH 4, recovered in 1974 from Laetoli, Tanzania. The largest contribution to the Au. afarensis hypodigm comes from Hadar, but other sites in Ethiopia (Belohdelie, Brown Sands, Dikika, Fejej, Maka, and White Sands) and sites in Kenya (Allia Bay, Koobi Fora, and West Turkana) have contributed to it. The temporal range of Au. afarensis is ca. 3.7–3 Ma (ca. 4–3 Ma if the presence of Au. afarensis is confirmed at Belohdelie and Fejej). The Au. afarensis hypodigm includes a well-preserved skull, partial and fragmented crania, many lower jaws, sufficient limb bones to be able to estimate stature and body mass (Kimbel and Delezene, 2009), and a specimen, A.L.-288, that preserves ca. 25% of the skeleton of an adult female. Most body mass estimates range from ca. 30–45 kg, and the endocranial volume of Au. afarensis is estimated to be between 400 and 550 cm3. It has smaller incisors than those of extant chimps/bonobos, but its premolars and molars are relatively larger. Comparative evidence suggests that the hind limbs of A.L.-288 are substantially shorter than those of a modern human of similar stature. The appearance of the

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