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In the Light of Evolution Volume IV: The Human Condition
P. aethiopicus is ca. 2.5–2.3 Ma. P. aethiopicus is similar to P. boisei (see above) except that the face is more prognathic, the cranial base is less flexed, the incisors are larger, and the postcanine teeth are not so large or morphologically specialized.
The most recent addition to the megadont archaic hominin hypodigm is Australopithecus garhi Asfaw et al. 1999 (Asfaw et al., 1999). It was introduced to accommodate specimens recovered in 1997 from Aramis in the Middle Awash study area, Ethiopia. The hypodigm is presently restricted to fossils recovered from the Hata Member in the Middle Awash study area, Ethiopia. The type specimen, the ca. 2.5-Ma BOU-VP-12/130, combines a primitive cranium with large-crowned postcanine teeth. However, unlike P. boisei (see above), the incisors and canines are large and the enamel apparently lacks the extreme thickness seen in the latter taxon. A partial skeleton with a long femur and forearm was found nearby but is not associated with the type cranium, and it has not been formerly assigned to Au. garhi. If the type specimen of P. aethiopicus (Omo 18.18) belongs to the same hypodigm as the mandibles that seem to match the Au. garhi cranium, then P. aethiopicus would have priority as the name for the hypodigm presently attributed to Au. garhi.
This group includes taxa that may belong to the human clade. However, most of the taxonomic assignments reviewed below take little or no account of the possibility that cranial and dental features assumed to be diagnostic of the human clade (e.g., foramen magnum position and canine size and shape) may be homoplasies (see below). Thus, for the reasons set out in the next section, rather than assume these taxa are hominins, the prudent course is to consider them as candidates for being early members of the human clade.
The type specimen, ARA-VP-6/1, of the taxon now called Ardipithecusramidus (White, Suwa, and Asfaw 1994) White, Suwa, and Asfaw 1995 (White et al., 1994, 1995) was recovered in 1993 from Aramis, in the Middle Awash study area, Ethiopia. All of the hypodigm come from the sites of Aramis, Kuseralee Dora, and Sagantole in the Central Awash Complex, Middle Awash study area, or from sites in the Gona study area, also in Ethiopia. The morphology of the Tabarin is such that it, too, could belong to the Ar. ramidus hypodigm. The temporal range of Ar. ramidus is ca. 4.5–4.3 Ma. The published evidence consists of two associated skeletons, one of which (ARA-VP-6/500) includes a partial skull and especially good preservation of the hands and feet, a piece of the base of the cranium, mandibles, associated dentitions, isolated teeth, two vertebrae, a first rib, fragments of long bones, and other isolated postcranial fossils. The