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Australopithecus Africanus

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Australopithecus Africanus Ramsaday college Australopithecus africanus Australopithecus africanus is an extinct species of australopithecine, the first species to be described. In common with the older Australopithecus afarensis, A. africanus was of slender build, or gracile, and was thought to have been a direct ancestor of modern humans. Fossil remains indicate that A. africanus was significantly more like modern humans than A. afarensis, with a more human-like cranium permitting a larger brain and more humanoid facial features. A. africanus has been found only in South Africa at four sites: Taung (1924), Sterkfontein (1935), Makapansgat (1948) and Gladysvale (1992). Important fossil discoveries In 1924, a fossil was rescued from a limestone quarry at Taung in South Africa by Raymond Dart who was a Professor of Anatomy in nearby Johannesburg. The now- famous Taung Child skull had a mixture of human-like and ape-like features. Dart believed it to be an early ancestor of humans and in 1925 he gave his ‘man-ape’ a new species name, Australopithecus africanus. Dart had difficulty convincing other scientists that this was a human ancestor, partly because at the time, many believed human ancestors had large brains and ape-like jaws whereas the Taung Child had the opposite set of features. Acceptance only arose in the late 1940s after Robert Broom’s discoveries of more fossils including those of adults. Since then, many hundreds of Australopithecus africanus fossils have been found in South Africa. Key specimens: • Sts 14: a partial skeleton discovered in1947 by Robert Broom and John Robinson in Sterkfontein, South Africa. The shape of this pelvis proved Australopithecus africanus was able to walk upright on two legs. The spine has six lumbar vertebrae in the lower back. This is a human-like rather than an ape-like feature as modern humans sometimes have six but usually have five lumbar vertebrae whereas modern African apes have five or less. • MLD 2: a lower jaw from an adolescent discovered in Makapansgat, South Africa • Taung Child: a partial skull and brain endocast discovered in 1924 in Taung, South Africa. This 2.3 million-year-old skull of a young child is the ‘type specimen’ or official representative of this species. It was the first fossil of a human ancestor ever found in Africa and was also the first to be classified in the genus Australopithecus. We know this individual was a young child because its first molar teeth were in the process of erupting from the jaw. Sk. Hedayet Hossain, Assistant Professor, Department of Anthropology Ramsaday college • Sts 71: a 2.5 million-year-old partial skull discovered in1947 by Robert Broom and John Robinson in Sterkfontein, South Africa. The robust features of this skull indicate it was an adult male. • ‘Mrs Ples’ or Sts 5: this 2.5 million-year-old skull discovered in 1947 by Robert Broom and John Robinson in Sterkfontein, South Africa. The skull was nicknamed ‘Mrs Ples’ because it was originally considered to be an adult female from the genus Plesianthropus. Later, it was decided that the skull was actually an Australopithecus africanus individual and there is also some debate about whether this skull was that of a female or male. Malapa hominins Fossils from two individuals were recovered in 2008 and announced as a new species Australopithecus sediba in 2010. More fossils are in the process of being excavated. Many other palaeontologists consider the ‘A. sediba’ fossils to be a chronospecies of A. africanus – meaning that the slight anatomical differences between the new fossils and A. africanus are due to changes over time within a species rather than them being from different species. This view makes the fossils merely an interesting side branch of our family tree but does extend the time range for A. africanus by almost half a million years Key physical features Body size and shape: • females grew to about 110 centimetres in height and males were slightly taller at about 135 centimetres • ape-like features included a cone-shaped rib cage and relatively long arms Brain: • averaged approximately 480 cubic centimetres. This was small but still relatively large when compared with a modern chimpanzee’s brain. Skull: • compared with the earlier species, Australopithecus afarensis, the skull showed some slightly more human-like features such as a smaller brow ridge and a slightly arched (rather than flat) forehead area. • like all human ancestors, the spinal cord emerged from the central part of the base of the skull rather than from the back. Jaws and teeth: • jaws and teeth were intermediate between those of humans and apes and those of earlier species, such as Australopithecus afarensis • the canine and incisor teeth had become shorter and smaller • a gap (diastema) between the canines and adjacent teeth was rare Sk. Hedayet Hossain, Assistant Professor, Department of Anthropology Ramsaday college • premolar teeth and molar teeth were all quite large Limbs: • leg and foot bones indicate that this species had the ability to walk on two legs. • they also indicate some ape-like features including slightly curved finger and toe bones and arms that were quite long, although not longer than their legs. Pelvis: • was fully adapted for walking on two legs but compared with those of modern humans it was less rounded, had a narrower birth canal, and was not specialised for a striding gait. Phylogeny A. africanus is considered to be a gracile australopith by some and a robust australopith by others. Traditionally, the species was favored as the immediate ancestor of the Homo lineage, specifically of Homo habilis. However, some researchers have always believed that A. afarensis was the common ancestor of both A. africanus and the Homo lineage, suggesting a cladistic event had occurred at A. afarensis. This schema has gained popularity in recent years. However, with the new evidence being put forth for A. sediba, it seems that the A. africanus → Homo scenario was closer to the truth in that A. africanus and A. sediba are undoubtedly related and A. sediba shares many characteristics with genus Homo. While there is some support for A. africanus as ancestral to the more derived robust forms, that still leaves unresolved those characteristics shared between A. aethiopicus and both Paranthropus boisei and A. afarensis. Conclusions The africanus material is seen as different things by different people. Some see this as a regional variation or subspecies of afarensis, some see it as two completely different species, and some consider the africanus material to be the descendants of afarensis. Another important question that has been, is, and will probably always be debated is the question of whether the africanus material represents two or more species, a sexually dimorphic species, or a very variable species (especially with regards to inter- era speculation). The accepted view seems to be that they deserve separate species status due to both their differences from the afarensis material and their geographic separation from them. However, a very important question in debate is whether or not this species contributed to the modern human lineage. Sk. Hedayet Hossain, Assistant Professor, Department of Anthropology .
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