- Comparative Anatomy
Fossils for Australopithecus sediba were discovered at a cave locality in South Africa known as Malapa. The species name “sediba” derives from the seSotho word for “wellspring”1.
Au. sediba appears most similar to, and may derive from, Australopithecus africanus, but with a notable set of derived character traits. Relative to the earlier South African australopiths, Au. sediba exhibits an expanded brain case, lacks of pronounced nuchal crest, and exhibits several reduced character states including subnasal prognathism, zygomatic flaring, and postorbital constriction. Although Au. sediba’s cheek teeth are similar in morphology to Au. africanus, the parabolic dental arcade and reduced postcanine dentition are more similar to Homo. Likewise, Au. sediba exhibits an arched supraorbital torus, a relatively square face, and a slight “chin”, also seen in Homo.
Au. sediba was assigned to Australopithecus based its overall body plan1. Primitive cranial traits include a relatively small brains size, prominent canine juga, and a pronounced glabella. Much like other South African australopiths and paranthropines, the masseter originates high on the cranium. Postcranially, Au. sediba is typical of Australopithecus in its small body size and relatively long arms. However, the Au. sediba pelvis exhibits a set of novel traits that hint at the later Homo condition, such as reduced distances between the hip joint and the ischial tuberosity and between the hip joint and the sacroiliac joint. Of particular note are hand morphologies that suggest the species was capable of a precision grip.
This species most likely exhibited slight sexual dimorphism, but because the two specimens used for analysis consists of an adult female and a juvenile male, it is difficult to estimate and compare their body sizes1.
Early analysis of the Au. sediba fossils suggests that the species is more derived than other australopiths, and trends toward early Homo1. If Au. sediba does represent an intermediate species between earlier Australopithecus and Homo, then several fossil currently attributed to Homo habilis, (e.g., Stw 53, KNM-ER 3735, and OH 62) may need to be reexamined1.
The type specimen for Au. sediba is MH1, a juvenile represented by a cranial and post cranial material that dates between 1.95 and 1.78 Ma.
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